Authors. Public Report

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2 Public Report This report has been prepared by the Institute of Geological and Nuclear Sciences Limited (GNS Science) exclusively for and under contract to Environment Canterbury. Unless otherwise agreed in writing, all liability of GNS Science to any other party other than Environment Canterbury in respect of the report is expressly excluded. The data presented in this Report are available to GNS Science for other use from August 2007 Authors Mark Stirling 1, Matthew Gerstenberger 1, Nicola Litchfield 1, Graeme McVerry 1, Warwick Smith 1, Jarg Pettinga 2 and Philip Barnes 3 1 GNS Science, PO Box , Lower Hutt 2 Natural Hazards Research Centre, Department of Geological Sciences, University of Canterbury, Private Bag, 4800, Christchurch 3 National Institute of Water and Atmospheric Research, Greta Point Private Bag, Wellington Project Number: 430W1209

3 CONTENTS EXECUTIVE SUMMARY...III 1.0 INTRODUCTION ACTIVE TECTONICS AND HISTORICAL SEISMICITY PROBABILISTIC SEISMIC HAZARD ANALYSIS Method and Analysis Earthquake Sources Faults Distributed Earthquake Sources Attenuation Model Computation of Hazard Hazard Estimates Loadings Standard Context REVIEW OF EARTHQUAKE SCENARIOS SUMMARY AND CONCLUSIONS RECOMMENDATIONS FOR FUTURE WORK ACKNOWLEDGEMENTS REFERENCES...19 FIGURES Figure 1 Figure 2a Figure 2b Figure 3 Figure 4 Figure 5 Figure 6a Figure 6b Figure 6c The plate tectonic setting of New Zealand, showing the relative plate motions (dark arrows with rates shown in mm/yr), the active fault traces, and the approximate boundary of the Canterbury region (dark dotted line)...26 The active fault sources used in the model, and a closer view of the Kaikoura region to show the complex fault source model described in the text for that area. (b). The index numbers correspond to the last column in Appendix The active fault sources used in the model. The index numbers correspond to the last column in Appendix Historical seismicity of the Canterbury region. The map shows all earthquakes that have been historically observed and/or instrumentally recorded from 1900 to 2006 Shallow crustal historical earthquakes of M>6.5 are shown for the timespan 1840 to the present Seismotectonic zones used for modelling the distributed seismicity input to the probabilistic seismic hazard analysis (PSHA). The zones are the same as those used in the national seismic hazard model (Stirling et al. 2002) and the updated national model (currently in preparation). The predominant slip-type, the Gutenberg-Richter parameters b (the b-value) and Mcutoff (the maximum magnitude modelled in the distributed seismicity model) are shown on the figure...30 Probabilistic seismic hazard maps of the Canterbury region. The 24 maps show the levels of peak ground acceleration (PGA, including magnitude weighted) and spectral acceleration (0.2, 0.5, 1 and 2 second period) for return periods of 50, 150, 475 and 1000 years on Class C (shallow soil) site conditions of McVerry et al. (2006). The accelerations are in units of g. Modified Mercalli Intensity (MMI) maps are shown for the same return periods. The maps are in order of PGA (a-d), 0.2 seconds spectral period (e-h), 0.5 seconds (i-l), 1 seconds (mp), 2 seconds (q-t) and MMI (u-x)...31 Deaggregation graphs to show the magnitude-distance contributions to the 475 year return period PGA at Kaikoura Deaggregation graphs to show the magnitude-distance contributions to the 475 year return period PGA at Christchurch Deaggregation graphs to show the magnitude-distance contributions to the 475 year return period PGA at Timaru GNS Science Consultancy Report 2007/232 i

4 TABLES Table 1 Table 2 Location-specific PGA (Period T(s)=0.0 sec), magnitude weighted PGA (MW), and response spectral acceleration (T(s)=0.08 to 3.0 sec) and MMI (last row) for various return periods (see column 1), and for class C (shallow soil) site conditions. The centres are listed in alphabetical order. Magnitude-weighted PGAs are frequently used in engineering studies, particularly where liquefaction is of significant concern. Liquefaction is most sensitive to the larger magnitude earthquakes, and these earthquakes are more heavily weighted in a magnitude-weighted versus raw PGA estimate Earthquake Scenarios for Kaikoura, Arthur s Pass, Rangiora, Kaiapoi, Christchurch, Ashburton, Temuka and Timaru. The distances shown are approximate distances from the closest point on the causative earthquake source to the centre...15 APPENDICES Appendix 1 Fault Source Parameters...48 Appendix 2 Glossary...51 GNS Science Consultancy Report 2007/232 ii

5 EXECUTIVE SUMMARY We provide an update of the 1999 Environment Canterbury (ECan) probabilistic seismic hazard model (Stirling et al. 1999, 2001) which incorporates new onshore and offshore fault data, new seismicity data, new methods for the earthquake source parameterisation of both datasets, and new methods for estimation of the expected levels of Modified Mercalli Intensity (MMI) across the region. We provide: (1) new probabilistic seismic hazard maps of the Canterbury region; (2) site specific probabilistic seismic hazard assessments for eight selected towns and cities in the region; and (3) a review of scenario earthquakes for the selected towns and cities. While the overall regional pattern of estimated hazard has not changed since the 1999 report, there has been a slight reduction in hazard in some areas (western Canterbury Plains and eastern Southern Alps), coupled with significant increases in hazard in one area (immediately northeast of Kaikoura). The new data and parameterisation of the fault source model, new distributed seismicity model, and new methods for estimating MMI are responsible for the differences in hazard from the 1999 study. Despite the changes to the probabilistic seismic hazard source model and estimates, the earthquake scenarios defined in the 1999 report are still generally relevant to the present model. GNS Science Consultancy Report 2007/232 iii

6 1.0 INTRODUCTION In this report we present the results of a probabilistic seismic hazard assessment (PSHA) for the Canterbury region, the work constituting Stage 2 of Environment Canterbury s (ECan s) Earthquake Hazard and Risk Assessment Study (Kingsbury et al. 2001). The study represents an update of the comprehensive PSHA carried out for ECan in 1999 (Stirling et al. 1999, 2001). The PSHA is carried out in much the same way as the older analysis, in that we combine geologic data describing the geometry and activity of the known active earthquake source faults in and around the Canterbury region with historical seismicity data to develop maps and site-specific estimates of expected earthquake shaking across the region. The update of the PSH model comprises new onshore and offshore fault data (the latter were only minimally considered in the older study), the use of improved methods to estimate the recurrence parameters for active faults, and the use of a new distributed seismicity model that incorporates the historical catalogue data accumulated since the older model was developed. Our PSH maps show the peak ground accelerations (PGAs), 5% damped response spectral accelerations (0.2, 0.5, 1 and 2 second periods) for 50, 150, 475 and 1000 years for uniform Class C (shallow soil) site conditions (McVerry et al. 2006). MMIs are provided for the same return periods. The hazard level with an average return period of 475 years corresponds to that expected to be reached with 10% probability in 50 years, the most frequently used measure of PSH in engineering and planning studies. We also present sitespecific probabilistic seismic hazard analyses (PSHAs) and information on scenario earthquakes for eight towns or cities (Kaikoura, Rangiora, Kaiapoi, Christchurch, Ashburton, Temuka, Timaru, and Arthur s Pass) as part of this study. Differences between the updated hazard estimates and those of the 1999 study are due to the combined effects of the new input data and methods. The new data and methodology are the same as are being used in the present update of the national seismic hazard model (i.e. update of Stirling et al. 2002). In subsequent text we refer to the Stirling et al. (1999, 2001) Canterbury PSH model as the 1999 study or 1999 model, and the Stirling et al. (2002) New Zealand PSH model as the Stirling et al. (2002) model or study, or simply the national seismic hazard model. 2.0 ACTIVE TECTONICS AND HISTORICAL SEISMICITY Much of the Canterbury region is located within a wide zone of active earth deformation associated with oblique collision between the Australian and Pacific plates, where relative plate motion is obliquely convergent across the plate boundary at about 40mm/yr at the latitude of Canterbury (De Mets et al. 1990; Fig 1). The oblique collision is largely accommodated by the Alpine Fault to the west of the Canterbury region (Faults 7 and 8 in Fig. 2), where dextral slip rates of 15-35mm/yr and uplift rates of around 10 mm/yr are observed (e.g. Berryman & Beanland, 1988; Berryman et al. 1992; Sutherland & Norris, 1995), and by dextral slip rates ranging from about 5 to 27 mm/yr on the Marlborough faults in the north of the region (the Wairau, Awatere, Clarence and Hope Faults; Langridge et al. 2003; faults 1-4, 9-14, and in Fig. 2). The remaining component of plate motion is GNS Science Consultancy Report 2007/232 1

7 distributed widely across the central and southern parts of the region, and is expressed by the presence of strike-slip and reverse faults with slip rates of less than 10 mm/yr. Historical seismicity (Fig. 3) is most prolific in the northern and western parts of the Canterbury region, where there is also geological evidence of widespread active earth deformation. Several moderate-to-large (M>6.5) shallow (<15 km) earthquakes have occurred in the Canterbury region since the inception of historical records in The earliest of these earthquakes was the M Marlborough earthquake, which ruptured the northeastern section of the Awatere Fault (Grapes et al. 1998). The M North Canterbury earthquake ruptured the central section of the Hope Fault (e.g. Cowan, 1991; Pettinga et al. 1998, 2001). Also, the Poulter Fault (Fault 24 in Fig. 2) has been defined as the source of the M Arthur s Pass earthquake (Berryman & Villamor 2004). Aside from these earthquakes, no other ground rupturing earthquakes have occurred in the region in historic time. For instance, the Alpine Fault has remained as a seismic gap for the entire historic period. However, geological investigations along the Alpine Fault provide evidence for the occurrence of great earthquakes (M>8) with recurrence intervals of a few hundred years (e.g. Yetton, 1998; Sutherland et al. 2006), so the present lack of activity along the fault is due to the historic period coinciding with the time between these earthquakes. Seismotectonic zonation of the Canterbury region is based on the zones defined for the national seismic hazard model (Stirling et al. 2002). This differs from the 1999 study, which divided the region into six structural domains according to Pettinga et al. (1998). The zones we use are shown in Figure 4. Use of the Stirling et al (2002) zones is for consistency of approach to that of the national seismic hazard model. 3.0 PROBABILISTIC SEISMIC HAZARD ANALYSIS 3.1 Method and Analysis The PSHA methodology of Cornell (1968) forms the basis for our analysis. The steps taken to undertake our PSHA are: (1) use geologic data and the historical earthquake record to define the locations of earthquake sources and the likely magnitudes and frequencies of earthquakes that may be produced by each source; and (2) estimate the ground motions that the sources will produce at a grid of sites that covers the entire region. The computation of ground motions in (2) is achieved with a seismic hazard computer code corresponding to that developed by Stirling et al. (2002). 3.2 Earthquake Sources Faults We show the fault sources used in our PSHA in Figure 2, and list them in Appendix 1. The new fault data are obtained from the GNS active fault database ( from recent field notes and recently completed university theses at the University of Canterbury (see references in Appendix 1), and from the National Institute of Water and Atmospheric Research (NIWA) offshore active fault database (see references in Appendix 1). Fault sources surrounding the Canterbury region have also been included as input to the GNS Science Consultancy Report 2007/232 2

8 PSHA, since these have the potential to contribute to the hazard inside the boundaries of the region. Much of the update of the fault model has happened by way of a series of meetings of an expert panel based at GNS Science, NIWA and the University of Canterbury over the period July 2006 to January 2007 for onshore faults, and 2002 to 2007 for offshore faults (see Acknowledgements for a complete list of contributors). Considerable attention has also been given to reconciling plate motion rates with cumulative slip rates across the region, and onshore-offshore correlations of faults and slip rates. The fault traces shown on Figure 2 are generalisations of the mapped fault traces. These generalised representations are appropriate for regional scale PSHA. Unlike the 1999 study, we use a single method for estimating the likely characteristic magnitude (M max ) and recurrence interval of M max earthquakes for each fault source in Figure 2. This method utilizes newly developed regression equations of moment magnitude (M w ) on fault area for New Zealand earthquakes (Villamor et al. 2001; Berryman et al. 2002), an internationally-based regression for plate boundary strike-slip faults (Hanks & Bakun 2002), and a method for calculating recurrence interval that was developed by the expert panel for update of the national seismic hazard model. The equations and method are as follows: M w = /3logW + 4/3logL (1) for New Zealand reverse and oblique-slip earthquakes (Berryman et al. 2002), in which W is fault width in km, and L is fault length in km M w = logA (2) for New Zealand normal-slip earthquakes (Villamor et al. 2001), in which A is the fault area in km 2 M w = /3logA (3) for global plate boundary strike-slip earthquakes (Hanks & Bakun, 2002), in which A is the fault area in km 2 logmo= M w (4) for global earthquakes (Hanks & Kanamori, 1979), in which Mo is seismic moment and M w is moment magnitude Mo = ulwd (5) for global earthquakes (Aki & Richards, 1980), in which ulwd are rigidity modulus (3e+11 dyne/cm 2 ), fault length (cm), fault width (cm) and single event displacement (cm), respectively. RI = D/SR (6) for all earthquakes, in which D is single event displacement (mm) and SR is slip rate (mm/yr) GNS Science Consultancy Report 2007/232 3

9 The procedure for parameterisation of the fault sources is to estimate magnitude (M w ) from fault dimensions according to the most appropriate choice of Equations 1 to 3, use Equation 4 to estimate the seismic moment (Mo) of the earthquake, Equation 5 to solve for the single event displacement (D) of the earthquake, and Equation 6 to solve for the recurrence interval (RI) from the single event displacement (D) and the slip rate (SR). The derived recurrence interval is then checked (validated) against the paleoseismic data for that fault, and discrepancies are then reduced or eliminated by adjustment of the parameters. The new procedure provides a single general method for the parameterisation of fault sources, and is iterative, in that it involves the validation and subsequent adjustment of the derived recurrence intervals (RI) according to paleoseismic data until consensus agreement on the suitability of the parameters is reached. In the new parameterisation, many of the old sources in the 1999 report are combined and/or lengthened in order for equations 1 to 6 to produce recurrence intervals consistent with paleoseismic data. The reduction and/or lengthening of sources is done carefully and in a manner consistent with regional neotectonics and structure. Sources are also drawn to more closely match the actual fault traces. The new parameterisation has the benefit of eliminating the undesirable discrepancies and relatively short recurrence intervals that arose from the earlier methodology, which used different approaches to source parameterisation according to the quantity and quality of available data (an adaptation of the methodology used by the Working Group of California Earthquake Probabilities, 1995). Fewer fault sources exist in the new model as a result of the new methodology being applied to onshore Canterbury. Virtually all of the offshore faults used in the model (derived from NIWA) are new since the 1999 model was developed, and all have been parameterised according to the methodology outlined by equations 1 to 6 (above). The few offshore sources in the 1999 report have been substantially modified as a result of the new NIWA input. While validation of the resulting source parameters against paleoseismic data was not possible for the offshore faults, the offshore lengths, magnitudes and recurrence intervals were able to be assessed based on knowledge gained for the onshore faults. The preferred or mean parameters are shown in Appendix 1. It is worthwhile to briefly describe the most notable changes to the fault source model from the 1999 report. The source modelling for the Porters Pass Fault zone (referred to as Porters to Grey and fault 40 in Appendix 1 and Fig. 2) has been simplified from the 1999 report. A single through-going Porters Pass Fault zone source is defined for our PSHA, replacing the equally-weighted through-going and segmented Porters Pass models that were used together in the 1999 model (Pettinga et al. 1998, 2001). The generally short sources defined for the segmented model in the 1999 report were the Mt Grey, Mt Thomas, and Porters Pass-Coopers Ck-Glentui-Townshend sources (Stirling et al., 1999; 2001), all of which are amalgamated in our new model. Our methodology produces recurrence intervals that best match the paleoseismically-derived estimates of recurrence interval when a single through-going Porters Pass source is defined, as opposed to the very short recurrence intervals produced by the segmented model in the 1999 report. The faults beneath the Canterbury Plains have been redefined and parameterised based on new data from the University of Canterbury. The relevant faults are the Ashley, Springbank, Cust, Hororata and Springfield Faults (faults in Fig. 2 and Appendix 1), the latter three new since the 1999 report. GNS Science Consultancy Report 2007/232 4

10 Faults in the northeast of the region have been modelled in such a way that they allow for slip rate transfer from the Hope Fault to the offshore faults, whereas the absence of the latter in the 1999 model meant that fault sources and the associated slip rates abruptly terminated near the coast. The northeastern section of the Hope Fault is modeled by the Hope-Conway (fault 13) and Hope-Conway-offshore (fault 14) segments, with slip rates of 15 mm/yr and 5 mm/yr respectively. These faults are concurrent along the 81 km length of the Hope-Conway section, with the Hope-Conway-offshore segment continuing a further 40 km offshore. The 15 mm/yr slip rate of fault 13 is transferred to the combined Jordan Thrust-Kekerengu- Chancet Faults (faults 16 and 17), with the northeasterm part of the Kekerengu-Chancet system (fault 15) also modeled to take up the 1 mm/yr slip rate of the Fidget Fault (fault 18), immediately to the west. The Jordan-Kererengu-Chancet Fault consists of two concurrent segments with a combined slip rate of 15 mm/yr, most of this on a blind segment (fault 17) with the top surface at 3 km depth, with only 3.1 mm/yr of the slip rate being carried to the surface by the wider source (fault 16). A map showing these fault geometries is shown in Figure 2b. In general, the balancing of both slip rate along fault systems, and restoration of the plate motion rate across the region are important consideration in the new Canterbury PSH model. Further south, the faults of the Waitaki and Mackenzie areas have seen major updates as a result of seismic loading studies for hydroelectric power facilities (Berryman et al. 2002). The Wharekuri, Rostrievor-Big Gully, Otematapaio and Dryburgh SE Faults used in the 1999 report have been eliminated in the new model, largely through the interpretation of new field data, and the process of amalgamation to form longer sources as a result of our new methodology (Fig. 2 and Appendix). The most obvious example of this process is the new Ostler Fault source, a single source which amalgamates the three Ostler Fault sources defined in the 1999 report. Our methodology produces recurrence intervals that best match the paleoseismically-derived estimates of recurrence interval when a single through-going Ostler Fault source is defined, as opposed to the very short recurrence intervals produced by the segmented model in the 1999 report Distributed Earthquake Sources In addition to defining the locations, magnitudes and frequencies of large (M~7-7.9) to great (M>8) earthquakes on the crustal faults and subduction zones, we also allow for the occurrence of moderate-to-large distributed earthquakes (M5-7.0) both on and away from the major faults. Our reasons for considering distributed earthquakes in our PSHA are twofold. First, earthquakes of M<6.5 often occur on fault sources that have no surface expression, and have therefore escaped mapping by geologists. This is because the rupture widths of these earthquakes are usually less than the width of the seismogenic zone (e.g., Wesnousky, 1986). A good example of the type of earthquake is the M Arthur s Pass earthquake, which occurred on a previously unknown fault, and did not rupture to the surface. Second, since many historic M>6.5 earthquakes have not been able to be assigned to specific faults, the possibility exists that some future large earthquakes may also occur on faults not listed in Appendix 1. GNS Science Consultancy Report 2007/232 5

11 Our input data and methodology for characterizing the PSH from distributed earthquakes have been significantly updated since the 1999 model. We continue to use the same overall approach, in that the b-value of the Gutenberg-Richter distribution logn=a-bm (N=number of events > magnitude M, and a and b are empirical constants; Gutenberg & Richter, 1944) is calculated for each of the seismotectonic regions shown in Figure 4, and the a-value is calculated for each grid cell. However, the seismotectonic zones are now based on those used for the national seismic hazard model (Stirling et al. 2002). The model now incorporates seismicity data past 1997 (the cutoff year for the 1999 model) and up to 2005, and the a- value has been recalculated according to an adaptive kernel method (Stock & Smith, 2002). The adaptive kernel method allows the smoothing parameters for the a-value to vary according to the spatial distribution of seismicity, rather than simply using one set of parameters as in the 1999 model. Furthermore, the final a-value for each grid cell used in the PSHA is a maximum-likelihood estimate based on the various sub-catalogues identified in the New Zealand earthquake catalogue, a sub-catalogue being a space-time subset of the catalogue with a complete record above a specific magnitude threshold. In contrast, the 1999 model used the maximum a-value from any of the identified sub-catalogues as the final a- value, which created unusually high assigned hazard levels in areas where some of the early historical moderate-to-large earthquakes were located (e.g. vicinity of Cheviot and Murchison in Stirling et al. 1999). Finally, a grid resolution of 0.1 degrees in latitude and longitude is used for the distributed seismicity calculations, rather than the 0.2 degrees used in the 1999 model Attenuation Model The attenuation relationships used in this study are the same as were used in the 1999 study (now published in McVerry et al. 2006). The model provides 5% damped acceleration response spectra (SA(T)) from a data set of New Zealand earthquakes, and takes account of the different tectonic types of earthquakes in New Zealand (i.e. crustal, subduction interface and dipping slab). The attenuation expressions for crustal earthquakes have further subdivisions, through mechanism terms, for different types of fault rupture (strike-slip, normal, oblique/reverse and reverse). The McVerry model is therefore used in this study because it has specific relevance to New Zealand conditions, and makes use of all the available New Zealand strong-motion data that satisfy Quality Assurance selection criteria. It also uses some digital seismograph records converted to accelerograms to increase the number of rock records available. The New Zealand dataset lacks records in the near-source region, at distances of less than 11 km from the earthquake source, and at magnitudes greater than M w Accordingly, some constraints have been applied to the attenuation models for the near-source regions, and for large magnitudes. For PGA, this has been done by supplementing the New Zealand records with 66 overseas records at distances of 10 km or less from the source, and including them directly in the regression analysis for determining the model. In developing the response spectrum model, the approach was to perturb overseas models, constraining some parameters but allowing others to be free in the regression against the New Zealand data. The Abrahamson and Silva (1997) model was used as the starting point for crustal earthquakes, and the Youngs et al. (1997) model as the starting point for subduction zone earthquakes. The crustal and subduction zone models were linked through sharing common site class terms. The site class terminology used in this report is consistent with that adopted in GNS Science Consultancy Report 2007/232 6

12 NZS1170 and Table 3 of McVerry et al. (2006). Rock sites are defined as Class A and Class B, Shallow Soil sites as Class C, and Deep or Soft Soil sites as Class D ( NZS1170.5:2004; Standards New Zealand, 2004). In this study we calculate all PSH maps and site-specific estimates according to Class C Shallow Soil site conditions. 3.3 Computation of Hazard We use the locations, sizes, and recurrence intervals of earthquakes defined in our source model to estimate the PSH for a gridwork of sites with a grid spacing of 0.1 degrees in latitude and longitude, and also for the towns and cities (referred to as centres) of Kaikoura, Rangiora, Kaiapoi, Christchurch, Ashburton, Temuka, Timaru and Arthur s Pass. Our measures of PSH are the acceleration levels (stronger horizontal component of PGA, 5% damped response spectral acceleration at 0.2, 0.5, 1 and 2 seconds period) and MMI levels with return periods of 50, 150, 475 and 1000 years. For a given site, we: (1) calculate the annual frequencies of exceedance for a suite of ground motion levels for every possible earthquake from the magnitude, recurrence interval, and source-to-site distance of earthquakes predicted from the source model; (2) sum the results of (1) across all earthquakes to give the annual frequencies of exceedance for a suite of ground motion levels at the site due to all sources (i.e. the hazard curve), and; (3) find the ground motion levels the correspond to annual frequencies of 1/50, 1/150, 1/475 and 1/1000 years (corresponding to the four return periods of 50, 150, 475 and 1000 years of interest to ECan) at the site. In calculating the ground motions expected with a certain return period, we generally assume a Poisson model of earthquake occurrence, in that we base our estimates of hazard on the average time-independent rate of earthquake occurrence on each fault, and do not calculate time-dependent hazard that would take into account the elapsed time since the last earthquake on the fault. Such calculations are generally limited to faults like the San Andreas of California, for which a large amount of paleoseismic data have been gathered (e.g. Working Group of California Earthquake Probabilities, 1995). In the 1999 report we introduced such time-dependent calculations to the Alpine Fiordland to Kelly segment (fault 7) of the Alpine Fault (Berryman et al. 1998; Yetton et al., 1998), and here update these calculations according to the latest estimates of time-dependent probabilities for the fault (Rhoades & Van Dissen, 2003). Annual probabilities of (lognormal), (Weibull), and (Inverse Gaussian) are averaged to give a mean annual probability of In our calculation of ground motions with the McVerry et al. attenuation model we adopt the standard practice of modern PSHA and take into account the uncertainty in estimates of ground motion from the attenuation model in the calculation of PSH. The general method is to assume that each estimate of ground motion for a particular earthquake calculated with the attenuation equation at a site is the median of a log-normal distribution, with an associated standard deviation. The standard deviations are usually equal to about 0.5 in natural log units of ground motion. The median and standard deviation are then used to estimate the probability of exceedance for a suite of ground motion levels, with the probabilities of exceedance for each ground motion level multiplied by the earthquake rate to obtain the contribution of the earthquake to the overall exceedance rate of the ground motion at the site. The maps of MMI are calculated according to the methodology of Smith (2003), which uses Monte Carlo methods and MMI attenuation expressions to develop MMI hazard curves. This represents a significant improvement over the simplistic method of using a regression equation to convert from PGA to MMI in the 1999 report. The updated GNS Science Consultancy Report 2007/232 7

13 methodology is an extremely important component of the ECan study, given that the MMI maps produced in the 1999 study were the most frequently used maps in the years following completion of the report (various ECan staff, pers comm ). 3.4 Hazard Estimates In Figure 5 we show maps of the levels of PGA and 5% damped response spectral acceleration (0.2, 0.5, 1 and 2 second period) estimated for the Canterbury region for return periods of 50, 150, 475 and 1000 years. We also show maps of MMI for these return periods. A total of 24 maps are produced to show the five measures of acceleration and MMI at the four return periods. The 24 maps show very different patterns of hazard across the region (Fig. 5). In general the highest accelerations and MMIs tend to occur in the northeast to northwest of the region. These areas are in the vicinity of Arthur s Pass and Kaikoura, where major active faults are located (Alpine Fault, Kelly Fault, Hope Fault, Jordan Thrust, Kekerengu Fault and associated faults, and the offshore continuations). These are faults that accommodate most of the slip rate of the plate boundary. The highest levels of historical seismicity occur in the central Southern Alps and northeastern Canterbury (Fig. 3). PGAs of over 0.4g and MMIs of over 8 are estimated for these areas at the 475 year return period. The fault sources tend to have a more significant contribution to the hazard than the distributed sources for: (a) long spectral periods, and; (b) long return periods. The maps that show PGA or spectral acceleration at the shortest spectral periods (0.2 and 0.5 seconds), and the shortest return periods (50 and 150 years) are most strongly influenced by the distributed earthquake sources. This is because the distributed sources produce moderate-sized (M<7) earthquakes, and these generally produce more short period motion than long period motion. Also, the moderate-sized earthquakes have short recurrence intervals (tens of years). In contrast the maps that show longer term hazard (475 and 1000 year return period) are most strongly influenced by the large-to-great earthquakes estimated from the fault sources. This is because these earthquakes produce the strongest ground motions in the PSHA, but only at return periods of hundreds to thousands of years. Also, since the M>7 earthquakes tend to produce more long period motion than the distributed seismicity sources, the 1 and 2 second spectral acceleration maps for 475 and 1000 years are almost wholly controlled by the distribution of fault sources. Distributed seismicity dominates the hazard beyond the northern boundary of the region (Buller area), where faults are generally of low activity (recurrence intervals in the thousands to tens of thousands of years), but large historical earthquakes have occurred and then been followed by a high rate of seismicity to the present day. The overall regional pattern of estimated hazard has not changed greatly from the 1999 report, in that the areas of highest hazard are situated in the north and west of the region where the major plate boundary faults are located. However, there is an overall reduction in hazard over significant parts of the region from the 1999 report. Reductions of 0.1 to 0.2g or more are evident in the western Canterbury Plains and eastern Southern Alps. In general the reduced hazard is due to the overall reduction in the number of fault-derived earthquakes in the new fault source model. Fewer fault sources translate to fewer large earthquakes in the PSH calculations. Another significant reduction in hazard on the 475 year PGA map are to the northeast of the Canterbury Plains, and in the neighbouring Buller area to the north. This is mainly due to the maximum-likelihood model-derived a-values in the new distributed GNS Science Consultancy Report 2007/232 8

14 seismicity model producing lower hazard than the a-values developed in the 1999 model (see Section 3.2.2), and also due to the simplifying of the segmentation model (and consequent reduction of earthquake recurrence rates) for the Porters Pass Fault zone to the northwest of Christchurch (Porters to Grey source, or fault 40). The maps of MMI also show a decrease of up to 1 MMI unit from those of the 1999 report, reflecting the application of the Smith (2003) methodology to the new MMI maps. The only obvious increase in estimated hazard is to the immediate northeast of Kaikoura, where the new offshore sources and slip rate balancing of the faults in that area have increased the earthquake rates and consequent hazard (Section 3.2.1). We show in Table 1 the values of PGA and spectral acceleration (for a range of spectral periods) and MMI expected at the eight towns or cities of Canterbury, for a range of return periods. Each row represents a response spectrum for a given return period. Clearly, there are considerable differences in hazard for the eight centres. The highest estimates of PGA, spectral acceleration and MMI for Kaikoura and Arthur s Pass townships. This is not surprising, since Arthur s Pass and Kaikoura are the only two townships that are close to the most active faults sources in our PSHA. Both towns are also situated within or near to zones of high distributed seismicity rates. In contrast, the other centres are generally located away to the southeast of the fault sources and areas of high distributed seismicity, so the hazard at these cities and towns is considerably less than for Arthur s Pass and Kaikoura. In order of decreasing hazard are Rangiora, Kaiapoi, Ashburton, Christchurch, Temuka and Timaru. Aside from the ranking of Ashburton and Christchurch, there is a north to south decrease in hazard for these centres. The trend is due to the increasing distance from the centres to the vast majority of fault sources and highest distributed seismicity rates. Rangiora therefore shows the third highest estimates of hazard for the eight centres, and Timaru shows the lowest hazard. In general the hazard estimates for these sites have reduced from those of the 1999 report. Ashburton now has slightly higher hazard than Christchurch, whereas the reverse was the case in the 1999 report. We attribute this reversal in hazard ranking to the overall increase in earthquake recurrence intervals in the areas immediately northwest and northeast of the Canterbury Plains (see above). The effect is to give the contours of hazard a more coast-parallel trend and gentler gradient in the vicinity of Christchurch than the 1999 maps showed. Since the city of Christchurch is the largest urban centre in Canterbury, and has been the focus of various seismic hazard studies in the past, it is important to examine the results we have estimated for this city. First, the hazard at Christchurch is roughly intermediate for the eight centres. The 475 year PGA estimated for the city is 0.31g, 0.26g less than Arthur s Pass (0.57g), and about 0.05g greater than Timaru (0.26g). The 0.2 second spectral acceleration (i.e. for the shaking period most damaging to short buildings) expected for this return period for Christchurch is 0.89g, which is towards the lower end of hazard for the eight centres listed in Table 1 (ranks 6 th ). Second, our 475 year return period estimate of PGA (0.31g) is slightly less than the equivalent estimate from the 1999 report (0.37g). Several factors contribute to the differences between present and 1999 results. The maximumlikelihood model-derived a-values in the new distributed seismicity model will have produced lower rates of distributed earthquakes in the Cheviot area (site of several moderate-sized early historical earthquakes), and simplifying of the segmentation model for the Porters Pass Fault zone (Porters to Grey source, fault 40) will have reduced the overall estimated GNS Science Consultancy Report 2007/232 9

15 recurrence rate of moderate to large earthquakes immediately northwest of the city. Changes to these sources collectively control the small change to the estimated hazard of Christchurch. In all parts of the region reductions or increases in hazard from the 1999 report are reflected to the greatest extent at the long return periods (475 and 1000 years). Table 1 Location-specific PGA (Period T(s)=0.0 sec), magnitude weighted PGA (MW), and response spectral acceleration (T(s)=0.08 to 3.0 sec) and MMI (last row) for various return periods (see column 1), and for class C (shallow soil) site conditions. The centres are listed in alphabetical order. Magnitude-weighted PGAs are frequently used in engineering studies, particularly where liquefaction is of significant concern. Liquefaction is most sensitive to the larger magnitude earthquakes, and these earthquakes are more heavily weighted in a magnitude-weighted versus raw PGA estimate. Arthur s Pass Latitude 42.95S Longitude E T(s) 0.00 MW yrs yrs yrs yrs yrs yrs yrs yrs yrs yrs MMI 50yrs = 7-8; 150yrs = 8-9; 475yrs = 9-10; 1000yrs = 9-10 Ashburton Latitude 43.90S Longitude E T(s) 0.00 MW yrs yrs yrs yrs yrs yrs yrs yrs yrs yrs MMI 50yrs = 6-7; 150yrs = 7-8; 475yrs = 7-8; 1000yrs = 8-9 Christchurch Latitude 43.53S Longitude E T(s) 0.00 MW yrs yrs yrs yrs yrs yrs yrs yrs yrs yrs MMI 50yrs = 6-7; 150yrs = 7-8; 475yrs = 7-8; 1000yrs = 8-9 GNS Science Consultancy Report 2007/232 10

16 Kaiapoi Latitude 43.39S Longitude E T(s) 0.00 MW yrs yrs yrs yrs yrs yrs yrs yrs yrs yrs MMI 50yrs = 6-7; 150yrs = 7-8; 475yrs = 8-9; 1000yrs = 8-9 Kaikoura Latitude 42.41S Longitude E T(s) 0.00 MW yrs yrs yrs yrs yrs yrs yrs yrs yrs yrs MMI 50yrs = 7-8; 150yrs = 8-9; 475yrs = 9-10; 1000yrs = 9-10 GNS Science Consultancy Report 2007/232 11

17 Rangiora Latitude 43.31S Longitude E T(s) 0.00 MW yrs yrs yrs yrs yrs yrs yrs yrs yrs yrs MMI 50yrs = 6-7; 150yrs = 7-8; 475yrs = 8-9; 1000yrs = 8-9 Temuka Latitude 44.24S Longitude E T(s) 0.00 MW yrs yrs yrs yrs yrs yrs yrs yrs yrs yrs MMI 50yrs = 6-7; 150yrs = 7-8; 475yrs = 7-8; 1000yrs = 8-9 Timaru Latitude 44.40S Longitude E T(s) 0.00 MW yrs yrs yrs yrs yrs yrs yrs yrs yrs yrs MMI 50yrs = 6-7; 150yrs = 7-8; 475yrs = 7-8; 1000yrs = Loadings Standard Context The return periods considered in this report need to be put into context against New Zealand structural design requirements, which have changed between the 1992 Loadings Standard and the new standard published in GNS Science Consultancy Report 2007/232 12

18 In the 1992 New Zealand Loadings Standard NZS4203:1992 (Standards New Zealand, 1992), the strength of motion to be specifically considered in the design of normal structures (e.g. office buildings) corresponds to a nominal return period of 450 years, or approximately a 10% probability of exceedance in 50 years. The design requirements of the New Zealand Loadings Standard are intended to ensure that structures specifically designed for 450-year return period motions survive without collapse in even stronger motions, corresponding to return periods of about 2500 years to 5000 years or more. A minimum return period of 1000 years is to be specifically considered in design for important structures for which the loss of function would have a severe impact on society according to the Loadings Standard. This class includes structures such as essential hospital and medical facilities, radio and television transmitting facilities, telephone exchanges, and power stations and sub-stations. The requirements for more important structures have increased in the new standard NZS1170:2004 Structural Design Actions (Standards New Zealand, 2004). NZS1170 requires a return period of 500 years for the Ultimate Limit State for normal use structures (only a nominal change for NZS4203), with a longer return period of 1000 years for structures including Power-generating facilities, water treatment and waste water treatment facilities and other public utilities not designated as post-disaster, as in NZS4203. A major change is that a return period of 2500 years is now required for the Ultimate Limit State for buildings and facilities designated as essential facilities or with special post-disaster function as well as Utilities or emergency supplies or installations required as backup for buildings and facilities of Importance Level 4 (Importance Level 4 covers structures with special post-disaster functions). For all three classes of structure, a return period of 25 years is required for a Serviceability Limit State (SLS) requiring avoidance of damage that prevents a structure from being used as originally intended without repair. For Importance Class 4, there is an additional more onerous Serviceability Limit State requiring that the critical facilities remain operational in 500-year return-period motions, likely to be the governing design requirement for these types of structures. These requirements suggest that return periods of 2500 years should be considered in planning for post-disaster response. This is tempered by a deterministic upper limit on the design motions that must be considered, essentially corresponding to 84-percentile motions adjacent to the Alpine Fault. These will be less than the 2500-year motions in the regions of Canterbury with the highest seismic hazard, corresponding approximately to a peak ground acceleration of about 0.9g for Shallow Soil site conditions, which is less than the 2000-year motions for Kaikoura, for example. 4.0 REVIEW OF EARTHQUAKE SCENARIOS An important application of a PSHA is the development of earthquake scenarios for specific sites of importance and target return periods. For the ECan study these sites are the eight town or cities of Kaikoura, Rangiora, Kaiapoi, Christchurch, Ashburton, Temuka, Timaru and Arthur s Pass. A scenario earthquake is usually defined as the most realistic damaging earthquake that is expected to impact a site, and this event may be determined in a variety of ways. We construct and examine selected deaggregation graphs for several of the centres to review the extent to which the earthquake scenarios identified in the 1999 report are still valid GNS Science Consultancy Report 2007/232 13

19 for the new model. Our plots (Fig. 6) show the contribution to the 475 year return period PGA by sources sorted according to magnitudes and source-to-site distance for Kaikoura, Christchurch and Timaru. The height of the magnitude-distance bins (z-axis) represents the contribution to the exceedance rate of the 475 year PGA by each magnitude-distance bin. The deaggregation plot for Kaikoura shows fault sources to dominate the hazard. The two peaks on Figure 6a correspond to the large earthquakes at close distances produced by the Hope-Conway, Hundalee and Jordan Thrust sources (faults 13-17, and 31; M w at 11 km or less). Other fault sources, and the distributed seismicity make minimal contributions to the 475 year PGA by comparison. The most significant change is that distributed seismicity makes a lesser contribution to the hazard than in the 1999 report (the area of the graph at M<7 and distance <20 km). In Christchurch and Timaru the contribution to hazard is from an overall similar mix of sources to those of the 1999 report. The distributed seismicity model makes the largest contribution to the hazard of the two cities, with fault sources making a significant contribution at the largest magnitudes (Fig. 6b and 6c). In Christchurch (Fig. 6b) the new model gives increased contribution from fault sources and decreased impact from distributed seismicity, although the distributed sources are still more important. Peaks on the graph at the largest magnitude end of the graph are attributed to the Cust and Springbank Fault sources beneath the northeastern Canterbury Plains (M6.8 at km), and the Porters to Grey and Ashley Fault sources (M7.2 at km), slightly further to the northeast to northwest. In the case of Timaru (Fig. 6c), the relative contributions of fault and distributed sources are similar to the 1999 report, in that most of the 475 year hazard comes from distributed seismicity sources. The main fault source peak on the graph is the Hutt-Peel source (fault 49) at M7.2 and distance about 50 km. The exact mix of earthquakes making up the deaggregation plots has therefore changed slightly with our update of the source model. Kaikoura shows almost all the hazard to come from large earthquake sources at close distance, which was a clear conclusion from the 1999 report. Christchurch shows hazard to come from a combination of local earthquakes of moderate magnitude, and large earthquakes at distances of around 50 km. It is also important to note that Alpine Fault earthquakes are also likely to contribute significantly to the hazard for longer spectral periods (T>0.5 sec) in the centres, so a great Alpine Fault earthquake should still be considered as a realistic scenario earthquake. We show revised earthquake scenario descriptions for all centres in Table 2. GNS Science Consultancy Report 2007/232 14

20 Table 2 Earthquake Scenarios for Kaikoura, Arthur s Pass, Rangiora, Kaiapoi, Christchurch, Ashburton, Temuka and Timaru. The distances shown are approximate distances from the closest point on the causative earthquake source to the centre. Location Kaikoura Scenario M ~ earthquake close than 11 km away on the Hope Fault, Jordan Thrust or Hundalee Fault Possible consequences The scenario earthquake is expected to rupture one of the major fault sources near Kaikoura. Ground rupture and right-lateral displacement of up to 7m is expected during an earthquake on the easternmost Hope Fault (source 13), and significant vertical deformation (with or without surface rupture) accompanying an earthquake on the Jordan Thrust or Hundalee sources (sources 15 to 17, and 31). The scenario earthquake is expected to originate at a depth of less than 12 km, but strong shaking will occur in Kaikoura (PGAs of g and MMI>9 are predicted for the 475 year return period). The shaking could occur for up to 30 seconds, causing damage to all classes of buildings, with almost total loss of chimneys, movement of houses off foundations, and loss of brick veneers. Some older unreinforced masonry buildings will collapse completely. Rock falls and landslides are expected to occur along the limestone bluffs and soil slopes behind the township. Limited liquefaction may occur in a few locations near the coast and also along some of the river margins of the Kowhai, Kahutara, and Haupuku Rivers. Some roads and the main trunk railway will be closed by landslides and rockfalls in many places. An aftershock of about M6, and perhaps as many as 10 aftershocks of M5 are expected to occur along the fault rupture in the two months or so that follow the main shock, and these are expected to continue to impact buildings and transportation networks in and around Kaikoura. There is a likelihood of large rockslides, landslides and rock avalanches in the Seaward Kaikoura Range. This will lead to localised rapid fan aggradation of the coastal plain and major river floodplains, along with some associated river channel avulsion. Location Arthur s Pass Scenario M7.3 earthquake about 14 km away on the Kelly Fault and M ~ 8 earthquake about 32 km away on the Alpine Fault Possible consequences These earthquakes will be produced by rupture of both Kelly and Alpine Fault sources (faults 7 and 19, respectively). The Kelly Fault is the most likely source to produce the 475 year return period motions at Arthur s Pass at the shortest spectral periods (T<0.2s) and the Alpine Fault at the GNS Science Consultancy Report 2007/232 15

21 longer periods (T>0.2s). Strong shaking could occur in the town (MM >9 and PGAs of g are predicted at the 475 year return period) for a duration of up to half a minute for the Kelly Fault and up to one minute for the Alpine Fault source. Damage to many classes of buildings, with extensive loss of chimneys is expected, as well as movement of houses off foundations, and loss of brick veneers. Some older unreinforced masonry buildings will collapse completely. Rock falls and debris flows are likely to damage many parts of the main highway, especially near Arthur s Pass. Further down the valley some large landslides are expected to block the Bealey River. Railway and roading networks are expected to be extensively damaged in numerous places by rockfalls, landslides and bridge damage. Rock avalanches will occur near the Otira Viaduct and elsewhere in the mountainous terrain. An aftershock of about M7 may occur along the fault in the few weeks that follow the mainshock, along with tens to hundreds of M5-6 aftershocks in the six months or so that follow the mainshock. These are certain to cause further havoc in and around Arthur s Pass. Location Rangiora, Kaiapoi, Christchurch, Ashburton, Temuka and Timaru Scenario Local earthquake M ~ under the Canterbury Plains and closer than 20 km Possible consequences The earthquake will produce short (5 10 second) sharp shaking (MM 7 to 8, and PGA of 0.2 to 0.3g are predicted for the 475 year return period) with damage mainly confined to contents, cladding, chimneys etc. Loss of power and utilities will occur for a brief period. Minor liquefaction is possible in Christchurch and Kaiapoi, along with minor rock falls and some shallow landslides in Banks Peninsula. Over the following two to three weeks many aftershocks generally of M4 or less will occur in the vicinity of the mainshock. The closest historical analogues are the earthquakes of 1869 and 1870 (Stirling et al. 1999). Based on historical observations (Stirling et al. 1999) the strongest shaking (MM>7) will impact a very limited area of no more than about 5 km radius from the epicentre. Location Rangiora, Kaiapoi, Christchurch, Ashburton, Temuka and Timaru Scenario Foothills earthquake M ~ closer than 50 km Possible consequences This scenario earthquake will be more damaging than the local earthquake. It will originate on the faults located at or near the eastern foothills of the Southern Alps, and may produce strong shaking for up to GNS Science Consultancy Report 2007/232 16

22 30 seconds (MM>7 and PGA of 0.3 to 0.4g are shown for the 475 year return period for most of the centres). For Christchurch, Kaiapoi and Rangiora the most likely source of the foothills earthquake is the Ashley Fault (fault 42) with M w 7.3 and distance of less than 30 km, followed by the Porters to Grey source (fault 40) with M w 7.4 and distance less 45 km. Amplification of strong ground shaking and some liquefaction is expected in Christchurch city, and extending northward to Kaiapoi and beyond. Rockfalls and landslides will be common in the foothills and Banks Peninsula. Rockslides and rock avalanches could also be triggered in the mountainous foothills terrain. For the centres to the south the maximum motions are most likely to be produced by the Hutt-Peel source (fault 49), with M w 7.4, and a distance of about 40 km in the case of Timaru. Location Rangiora, Kaiapoi, Christchurch, Ashburton, Temuka and Timaru Scenario Alpine Fault earthquake M ~ 8 at km Possible consequences This earthquake will only be significant for the longer period accelerations (T>0.4s) in which the southernmost Alpine Fault source (fault 7) produces 0.4 to 0.6g in the centres at the 475 year return period. Shaking is expected to be considerably less than for the Foothills earthquake scenario, but the duration of shaking will be much longer (60 seconds or more). Damage to materials (e.g. furniture) inside tall buildings may occur as a result of the longer period or wavelength of the seismic waves that originate from this great earthquake. Substantial local amplification and liquefaction may occur in parts of Christchurch and Kaiapoi, with lateral spreading along many river and estuary margins. Rockfalls, rock avalanches and landslides will be expected in the foothills, along with some landslides in Banks Peninsula. It is possible that there will be major disruption to utilities and services, and this could continue for days to weeks. The many aftershocks that accompany the earthquake will probably not produce significant shaking in any of the towns or cities. The current annual probability for this earthquake is about 1/ SUMMARY AND CONCLUSIONS Our update of the ECan seismic hazard model has incorporated new onshore and offshore fault data, new seismicity data, new methods for the earthquake source parameterisation of both datasets, and new methods for estimating hazard in terms of MMI. This work has provided: (1) a PSHA of the Canterbury region, including location specific PSHAs for Shallow Soil site conditions for eight selected centres in the region; and (2) a review of scenario earthquakes for these centres. While the overall pattern of estimated hazard has not changed since the 1999 report, there has been a reduction in estimated hazard over a GNS Science Consultancy Report 2007/232 17

23 significant proportion of the western Canterbury Plains and eastern Southern Alps. The new data and parameterisation of the fault source model, new distributed seismicity model, and new methods of estimating MMI are responsible for the differences in hazard from the 1999 study. Our review of the earthquake scenarios defined in the 1999 report has resulted in some minor changes to the scenario descriptions, and we attribute these changes to the exact mix of fault and distributed seismicity sources in the new model. 6.0 RECOMMENDATIONS FOR FUTURE WORK Arguably, the biggest improvement to the estimates of hazard presented in this report would be made at a site-specific level. We therefore recommend that the Canterbury PSH model be augmented with site response information for sites of highest earthquake risk in the region. This would primarily be Christchurch, although other centres could be examined as second priority. Our collaborative group of GNS Science and University of Canterbury scientists have now had lengthy discussions about how the PSH model could be improved in this respect. The model is presently based on uniform site conditions, so any application at the site specific level needs to be adjusted according to site response information. Over the years this has been done by scientists and consulting engineers according to their own specific interests and needs, and the results vary greatly according to the various methods applied. We now have the necessary collaboration that would update the PSH estimates for Christchurch according to site condition information by way of a defensible consensus approach. We consider that a combination of existing literature and models could be combined with new data on such critical parameters as shear wave velocity and material properties (CPT and SPT results) to provide a meaningful site response map for the city. The map would then be used together with the dominant earthquakes in the PSH model to determine the PSH expected for a given event or return period. A study that combines use of existing literature with data acquisition should be multi-year, staged according to literature review and existing data acquisition, field acquisition, interpretation and modelling, and finally leading to a revised PSH model. The budget may be such that it requires additional funding from outside of ECan. 7.0 ACKNOWLEDGEMENTS We thank Helen Grant (ECan) and Timothy McMorran (ECan s external reviewer) for their reviews of the report. Helen Grant and Dawn Davison (ex ECan) are thanked for providing us with the opportunity to undertake this study. We are indebted to the following scientists for contributing their expertise, time and efforts to an intensive review of the recurrence parameters for the Canterbury region faults; Kelvin Berryman, Russ Van Dissen, Robert Langridge, Pilar Villamor, Andy Nicol, Kate Wilson and Roberto Basili. GNS Science Consultancy Report 2007/232 18

24 8.0 REFERENCES Abrahamson, N.A., and W.J. Silva (1997). Empirical response spectral attenuation relationships for shallow crustal earthquakes. Seismological Research Letters 68, Aki, K., and Richards, P.G Quantitative Seismology: Theory and Methods, W.H. Freeman, San Francisco, California. Barnes, P.M.; Mercier de Lépinay, B.; Collot, J-Y.; Delteil, J.; Audru, J-C., and GeodyNZ team, South Hikurangi GeodyNZ swath maps: depths, texture and geological interpretation. 1:500,000., N.Z. Oceanogr. Inst. Chart, Miscellaneous Series 75. National Institute of Water and Atmospheric Research, Wellington. Barnes, P.M., The southern end of the Wairarapa Fault, and surrounding structures in Cook Strait. The 1855 Wairarapa Earthquake Symposium, 150 years of thinking about magnitude 8+ earthquakes and seismic hazard in New Zealand, Museum of New Zealand Te Papa Tongarewa, 8-10 September, Proceedings Volume, compiled by J. Townend, R. Langridge, and A. Jones, pp Barnes, P.M Releasing and restraining bends on the strike-slip Alpine and Boo Boo faults, New Zealand: New structural insights and slip rates from high-resolution multibeam bathymetric data. Paper presented at the International Conference on Tectonics of strike-slip restraining and releasing bends in continental and oceanic settings, The Geological Society, London, September, Barnes, P.M.; Audru, J-C Quaternary faulting in the offshore Flaxbourne and southern Wairarapa basins, southern Cook Strait, New Zealand. New Zealand Journal of Geology and Geophysics 42, Barnes, P.M.; and Audru, J-C, Recognition of active strike-slip faulting from highresolution marine seismic reflection profiles: Eastern Marlborough Fault System, New Zealand. Geological Society of America Bulletin, 111, Barnes, P.M.; Mercier de Lépinay, B.; Collot, J-Y.; Delteil, J. Audru, J-C, Strain partitioning in the transition area between oblique subduction and continental collision: Hikurangi margin, New Zealand. Tectonics, 17: Barnes, P.M.; and Mercier de Lépinay, B Rates and mechanics of rapid frontal accretion along the very obliquely convergent southern Hikurangi margin, New Zealand. Journal of Geophysical Research, 102: 24,931-24,952. Barnes, P.M., Active folding of Pleistocene unconformities on the edge of the Australian Pacific plate boundary zone, offshore north Canterbury, New Zealand. Tectonics, 15: Barnes, P.M., Inherited structural control from repeated Cretaceous to Recent extension in the North Mernoo Fault Zone, western Chatham Rise, New Zealand. Tectonophysics, 23: Barnes, P.M., Continental extension of the Pacific Plate at the southern termination of the Hikurangi subduction zone: The North Mernoo Fault Zone, offshore New Zealand. Tectonics, 13: GNS Science Consultancy Report 2007/232 19

25 Barnes, P.M., Nodder, S.D. and Wright, I.C., Seismotectonic studies on the submerged New Zealand continental shelf: a status report. Proceedings, New Zealand National Society for Earthquake Engineering technical conference, Taupo. pp Barrell, D., Cox, S. In prep. Geology of the Aoraki Area. Institute of Geological & Nuclear Sciences 1: geological map sheet + x p. Lower Hutt, New Zealand. GNS Science. Barrell, D. J. A.; Langridge, R. M.; Berryman, K. R.; Lukovic, B Seismic Loads on Dams Waitaki System: Dryburgh Stonewall fault displacement characterisation. Institute of Geological & Nuclear Sciences Client Report 2004/56. Barrell, D. J. A., Van Dissen, R. J., Berryman, K. R., Read, S. A. L., Wood, P. R., Zachariason, J., Lukovic, B., Nicol, A., Litchfield, N. 2002: Seismic loads on dams Waitaki System, Aviemore Power Station, Geological Investigations for fault displacement characterisation. Institute of Geological & Nuclear Sciences Client Report 2001/125. Barrell, D. J. A., Van Dissen, R. J., Read, S. A. L. 2002: Aviemore Power Station, Summary of the displacement characterisation of geological faults underlying the Aviemore Earth Dam foundations. Institute of Geological & Nuclear Sciences Client Report 2002/40. Begg, J.G., Johnston, M.R Geology of the Wellington Area. Institute of Geological & Nuclear Sciences 1: geological map sheet + 64 p. Lower Hutt, New Zealand. Institute of Geological & Nuclear Sciences Limited. Bennett, E.R.; Youngson, J.H.; Jackson, J.A.; Norris, R.J.; Raisebeck, G.M.; Yiou, F.; Fielding, E Growth of South Rough Ridge, Central Otago, New Zealand: using in situ cosmogenic isotopes and geomorphology to study an active, blind reverse fault. Journal of Geophysical Research 110, B02404, doi: /2004jb Benson, A. M., Little, T. A., Van Dissen, R. J., Hill, N., Townsend, D. B. 2001: Late Quaternary paleoseismic history and surface rupture characteristics of the eastern Awatere strike-slip fault. Geological Society Of America Bulletin 113: Berryman, K.R., and Beanland, S. 1988: The rate of tectonic movement in New Zealand from geological evidence.transactions of the Institute of Professional Engineers of New Zealand 15: Berryman, K.R., Beanland, S., Cooper, A.F., Cutten, H.N., Norris, R.J., Wood, P.R. 1992: The Alpine Fault, New Zealand: Variation in Quaternary structural style and geomorphic expression. Annales Tectonicae Suppliment to Volume 6: Berryman, K., Webb, T., Hill, N., Stirling, M., Rhoades, D., Beavan, J., Darby, D., Seismic loads on dams, Waitaki system. Earthquake Source Characterisation. Main report. GNS client report 2001/129 Berryman, K. R., Van Dissen, R. J., Mouslopoulou, V. 2002: Recent Rupture of the Tararua section of the Wellington Fault and relationships to other fault sections and rupture segments. New Zealand Earthquake Commission Research Report 97/248. Institute of Geological and Nuclear Sciences, Lower Hutt, New Zealand: 22 pp. GNS Science Consultancy Report 2007/232 20

26 Collot, J-Y; Delteil, J; Lewis, K; et l'equipe scientifique: Audru, J-C; Barnes, P; Chanier, F; Chaumillon, E; Davy, B; Lallemand, S; Lamarche, G; Mercier de Lepinay, B; Orpin, A; Pelletier, B; Sosson, M; Toussaint, B; and Uruski, C From the Kermadec trench to the southern termination of the Hikurangi Trough: results of the GEODYNZ SUD, Leg 1 swath-mapping survey. Comptes Rendu de l' Acadamie des Sciences, Paris, t.320, Series II a, P Cornell, C.A Engineering seismic risk analysis. Bulletin of the Seismological Society of America 58, Cowan, H.A., 1991: the North Canterbury earthquake of 1 September, Journal of the Royal Society of New Zealand 21:1-12. DeMets, C., Gordon, R.G., Argus, D.F., and Stein, S Current plate motions. Geophysical Journal International 101: Estrada, B.E. (2003). Seismic Hazard Associated with the Springbank Fault, North Canterbury Plains. Unpublished MSc (Eng. Geol.) Thesis, University of Canterbury Library, Christchurch, New Zealand. Forsyth, P.J Geology of the Waitaki Area. Institute of Geological & Nuclear Sciences 1: geological map sheet + 64 p. Lower Hutt, New Zealand. Institute of Geological & Nuclear Sciences Limited. Fraser, J.G Paleoseismic investigation of the Waimea-Flaxmore Fault System, Nelson Region. MSc Thesis, University of Canterbury. Grapes, R., Little, T., and Downes, G Rupturing of the Awatere Fault during the 1848 October 16 Marlborough earthquake, New Zealand: historical and present day evidence. New Zealand Journal of Geology and Geophysics 41: Gutenberg, B. and Richter, C.F. 1944: Frequency of earthquakes in California. Bulletin of the Seismological Society of America 34: Hanks, T.C. and Bakun, W.H A bilinear source-scaling model for M-logA observations of continental earthquakes. Bulletin of the Seismological Society of America 92, Hanks, T.C. and Kanamori, H A moment magnitude scale. Journal of Geophysical Research 84, Howard ME Holocene surface-rupturing earthquakes along the Porters Pass Fault. Unpublished MSc thesis, University of Canterbury, Christchurch, New Zealand. Howard, M., Nicol, A., Campbell, J. Pettinga, J.R Holocene paleoearthquakes on the strike-slip Porters Pass Fault, Canterbury, New Zealand. New Zealand Journal of Geology and Geophysics 48: Kingsbury, P., Pettinga, J.R., and Van Dissen, R.J., Earthquake hazard and risk assessment study for the Canterbury region: Outline of programme development. Bulletin of the New Zealand Society for Earthquake Engineering. 34(4), GNS Science Consultancy Report 2007/232 21

27 Langridge, R. M.; Berryman, K. R. 2005: Morphology and slip rate of the Hurunui section of the Hope Fault, South Island, New Zealand. New Zealand Journal of Geology and Geophysics 48: Langridge, R. M., Campbell, J., Hill, N. L., Pere, V., Pope, J., Pettinga, J., Estrada, B., Berryman, K. R. 2003: Paleoseismology and slip rate of the Conway segment of the Hope Fault at Greenburn Stream, South Island, New Zealand. Annals of Geophysics 46 (5): Langridge, R. M., Berryman, K. R., Van Dissen, R. J. 2005: Geometric segmentation and Holocene slip rate of the Wellington Fault New Zealand: the Pahiatua Section. New Zealand Journal of Geology and Geophysics 48 (4): Litchfield, N. J.; Campbell, J. K.; Nicol, A. 2003: Recognition of active reverse faults and folds in North Canterbury, New Zealand, using structural mapping and geomorphic analysis. New Zealand Journal of Geology and Geophysics 46: Litchfield, N.; McVerry, G.; Smith, W.; Berryman, K.; Stirling, M Seismic hazard study for Tailings Emankments at Macraes Gold Project. Institute of Geological & Nuclear Sciences Client Report 2005/135. Litchfield, N. J., Van Dissen, R. J., Langridge, R. M., Heron, D., Prentice, C. 2004: Timing of the most recent surface rupture event on the Ohariu Fault near Paraparaumu, New Zealand. New Zealand Journal of Geology and Geophysics 47 (1): Litchfield, N. J., Van Dissen, R. J., Heron, D., Rhodes, D. 2006: Constraints on the timing of the three most recent surface rupture events and recurrence interval for the Ohariu Fault: trenching results from MacKays Crossing, Wellington, New Zealand. New Zealand Journal of Geology and Geophysics 49: Long, D. T., Cox, S. C., Bannister, S., Gerstenberger, M. C., Okayam D. 2003: Upper crustal structure beneath the eastern Southern Alps and the MacKenzie Basin, New Zealand, derived from seismic reflection data. New Zealand Journal of Geology and Geophysics 46: Markley, M., Tikoff, B. 2003: Geometry of the folded Otago peneplain surface beneath Ida valley, Central Otago, New Zealand, from gravity observations. New Zealand Journal of Geology and Geophysics 46: Mason, D. P. M., Little, T. A. 2006: Refined slip distribution and moment magnitude of the 1848 Marlborough earthquake, Awatere Fault, New Zealand. New Zealand Journal of Geology and Geophysics 49: Mason, D. P. M., Little, T. A., Van Dissen, R. J. 2006: Refinements to the paleoseismic chronology of the eastern Awatere Fault from trenches near Upcot Saddle, Marlborough, New Zealand. New Zealand Journal of Geology and Geophysics 49: Mason, D. P. M., Little, T. A., Van Dissen, R. J. 2006: Rates of active faulting during late Quaternary fluvial terrace formation at Saxton River, Awatere fault, New Zealand. GSA Bulletin 118: McFarlane, D., Van Dissen, R. 2002: Aviemore Dam development of inputs for fault displacement analysis. Technical Memorandum prepared for Meridian Energy Ltd. GNS Science Consultancy Report 2007/232 22

28 McVerry, G. H; Langridge, R. 2004: Estimation of earthquake spectra for Opuha Dam site. Institute of Geological & Nuclear Sciences Client Report 2004/179. McVerry, G.H., Zhao, J.X., Abrahamson, N.A., Somerville, P.G New Zealand acceleration response spectrum attenuation relations for crustal and subduction zone earthquakes. Bulletin of the New Zealand Society of Earthquake Engineering 38(1), Nathan, S., Rattenbury, M.S., Suggate, R.P Geology of the Greymouth Area. Institute of Geological & Nuclear Sciences 1: geological map sheet + 58 p. Lower Hutt, New Zealand. Institute of Geological & Nuclear Sciences Limited. Nicol, A., Van Dissen, R. J., Vella, P., Alloway, B., Melhuish, A. 2002: Growth of contractional structures during the last 10 m.y. at the southern end of the emergent Hikurangi forearc basin, New Zealand. New Zealand Journal of Geology and Geophysics 45 (3): Nicol, A. and Van Dissen, R. J. 2002: Up-dip partitioning of displacement components on the oblique-slip Clarence Fault, New Zealand. Journal of Structural Geology 24: Norris, R. J. and Cooper, A. F. 2001: Late Quaternary slip rates and slip partitioning on the Alpine Fault, New Zealand. Journal of Structural Geology 23: Norris, R. J., Cooper, A. F., Wright, T., and Berryman, K Dating of past Alpine Fault rupture in South Westland. EQC Research Report 99/341. Norris, R.J.; Nicolls, R Strain accumulation and episodicity of fault movements in Otago. EQC Research Report 01/445. Pace, B.; Stirling, M. W.; Litchfield, N. J.; Rieser, U New active fault data and seismic hazard estimates for west Otago, New Zealand. New Zealand Journal of Geology and Geophysics 48: Pettinga, J.R., Chamberlain, C.G., Yetton, M.D., Van Dissen, R.J., and Downes, G., 1998: Earthquake Hazard and Risk Assessment Study (Stage 1 Part A); Earthquake Source Identification and Characterisation. Canterbury Regional Council Publication U98/10. Pettinga, J.R., Yetton, M.D., Van Dissen, R.J., and Downes, G.D Earthquake source identification and characterisation for the Canterbury region, South Island, New Zealand. Bulletin of the New Zealand Society of Earthquake Engineering 34(4), Rattenbury, M.S., Cooper, R.A., Johnston, M.R Geology of the Nelson Area. Institute of Geological & Nuclear Sciences 1: geological map 9. 1 sheet + 67 p. Lower Hutt, New Zealand. Institute of Geological & Nuclear Sciences Limited. Rattenbury, M.S., Townsend, D.B., Johnston, M.D Geology of the Kaikoura Area. Institute of Geological & Nuclear Sciences 1: geological map sheet + 70 p. Lower Hutt, New Zealand. GNS Science. Rhoades, D. A. and Van Dissen, R. J. 2003: Estimates of the time-varying hazard of rupture of the Alpine Fault, New Zealand, allowing for uncertainties. New Zealand Journal of Geology and Geophysics 46 (4): Smith, W.D., Earthquake hazard and risk assessment in New Zealand by Monte Carlo methods. Seismological Research Letters, 74, GNS Science Consultancy Report 2007/232 23

29 Standards New Zealand, (1992). Code for Practice for General Structural Design and Design Loadings for Buildings. Volume 1: Code of practice. NZS 4203:1992. Standards New Zealand, (2004). Structural Design Actions Part 5 Earthquake Actions New Zealand. Standard NZS1170.5:2004. Stirling, M.W., Wesnousky, S.G. and Berryman, K.R., Probabilistic seismic hazard analysis of New Zealand. New Zealand Journal of Geology and Geophysics 41, Stirling, M.W., Yetton, M., Pettinga, J., Berryman, K., amd Downes, G., Probabilistic seismic hazard assessment and earthquake scenarios for the Canterbury Region, and historic earthquakes in Christchurch. GNS client report 1999/53. Stirling, M.W., Pettinga, J., Berryman, K.R., and Yetton, M Probabilistic seismic hazard assessment of the Canterbury region, New Zealand. Bulletin of the New Zealand Society of Earthquake Engineering 34, Stirling, M.W., McVerry, G.H., Berryman, K.R., A new seismic hazard model for New Zealand. Bulletin of the Seismological Society of America.92, Stirling, M.W. and Barnes, P.M. (2003). Seismic hazard model for New Zealand. Natural Hazards Update 4: 1. Stock, C. and Smith, E.G.C Comparison of seismicity models generated by different kernel estimations. Bulletin of the Seismological Society of America 92, Sutherland, R., Berryman, K. R., Norris, R. J. 2006: Displacement rate on the Alpine Fault determined from offset glacial landforms between Milford Sound and the Cascade Valley: implications for the kinematics and seismic hazard of southern New Zealand. Geological Society Of America Bulletin 118(3/4): Sutherland, R., Norris, R.J. 1995: Late Quaternary displacement rate, paleoseismicity, and geomorphic evolution of the Alpine Fault: evidence from Hokuri Creek, South Westland, New Zealand. New Zealand Journal of Geology and Geophysics 38: Sutherland, R., Eberhart-Philips, D., Harris, R.A., Stern, T., Beavan, J., Ellis, S., Henrys, S., Cox, S., Norris, R.J., Berryman, K.R., Towend, J., Bannister, S., Pettinga, J., Leitner, B., Wallace, L., Little, T.A., Cooper, A.F., Yetton, M., Stirling, M.W., Do great earthquakes occur on the Alpine fault in central South Island, New Zealand? Geophysical Monograph, SIGHT. American Geophysical Union. Upton, P, Craw, D., James, Z., Koons, P. O. 2004: Structure and late Cenozoic tectonics of the Southern Two Thumb Range, mid Canterbury, New Zealand. New Zealand Journal of Geology and Geophysics 47: Van Dissen, R.; Barrell, D.; Langridge, R.; Litchfield, N.; Villamor, P.; Tonkin, P. 2007: Reassessment of seismic hazard at the Clyde Dam, Central Otago: Earthquake geology field investigations and determination of Dunstan Fault rupture characteristics. GNS Science Consultancy Report 2006/147. Villamor, P., Berryman, K., Webb, T., Stirling, M., McGinty, P., Downes, G., Harris, J., Litchfield, N., Waikato seismic loads - Task 2.1. Revision of seismic source characterisation. GNS client report 2001/59. GNS Science Consultancy Report 2007/232 24

30 Walters, R.A.; Barnes, P.; Goff, J.R Locally generated tsunami along the Kaikoura coastal margin: Part 1. Fault ruptures. New Zealand Journal of Marine and Freshwater Research. 40: 1 16 Wesnousky, S.G. 1986: Earthquakes, Quaternary faults and seismic hazard in California. Journal of Geophysical Research 91: Working Group of California Earthquake Probabilities, Seismic hazards in southern California, probable earthquakes Bulletin of the Seismological Society of America 85, Yetton, M.D., Wells, A., and Traylen, N.J., 1998: The probability and consequences of the next Alpine Fault earthquake. EQC Research Report 95/193. Youngs, R.R., Chiou, S.-J., Silva, W.J., and Humphrey, J.R Strong ground motion attenuation relationships for subduction zone earthquakes, Seismological Research Letters, 68(1), Zachariasen, J., Berryman, K. R., Langridge, R. M., Prentice, C., Rymer, M., Stirling, M. W., Villamor, P. 2006: Timing of late Holocene surface rupture of the Wairau Fault, Marlborough, New Zealand. New Zealand Journal of Geology and Geophysics 49: GNS Science Consultancy Report 2007/232 25

31 Figure 1 The plate tectonic setting of New Zealand, showing the relative plate motions (dark arrows with rates shown in mm/yr), the active fault traces, and the approximate boundary of the Canterbury region (dark dotted line). GNS Science Consultancy Report 2007/232 26

32 55 Figure 2a The active fault sources used in the model, and a closer view of the Kaikoura region to show the complex fault source model described in the text for that area. (b). The index numbers correspond to the last column in Appendix 1. GNS Science Consultancy Report 2007/232 27

33 Blenheim (15) Kekerengu-Chancet (18) Fidget (16) Jordan-Keke-Chancet (17) Jordan Blind-Keke-Chancet (14) Hope (Conway Offshore) Kaikoura (13) Hope (Conway) Figure 2b The active fault sources used in the model. The index numbers correspond to the last column in Appendix 1. GNS Science Consultancy Report 2007/232 28

34 Figure 3 Historical seismicity of the Canterbury region. The map shows all earthquakes that have been historically observed and/or instrumentally recorded from 1900 to 2006 (source: Shallow crustal historical earthquakes of M>6.5 are shown for the timespan 1840 to the present, and are as follows (numbered according to those shown on the map): 1. M Marlborough 2. M North Canterbury 3. M Cheviot 4. M Buller 5. M Arthur s Pass 6. M Inangahua 7. M Avoca GNS Science Consultancy Report 2007/232 29

35 Reverse b=1.07 Mcutoff=7.7 Reverse b=1.05 Mcutoff=7.0 Strike-slip b=1.13 Mcutoff=7.0 Strike-slip & reverse b=0.89 Mcutoff=7.0 Reverse b=1.0 Mcutoff=7.0 Reverse b=1.0 Mcutoff=7.0 Figure 4 Seismotectonic zones used for modelling the distributed seismicity input to the probabilistic seismic hazard analysis (PSHA). The zones are the same as those used in the national seismic hazard model (Stirling et al. 2002) and the updated national model (currently in preparation). The predominant slip-type, the Gutenberg-Richter parameters b (the b-value) and Mcutoff (the maximum magnitude modelled in the distributed seismicity model) are shown on the figure. GNS Science Consultancy Report 2007/232 30

36 Figure 5a Figure 5a-x Probabilistic seismic hazard maps of the Canterbury region. The 24 maps show the levels of peak ground acceleration (PGA, including magnitude weighted) and spectral acceleration (0.2, 0.5, 1 and 2 second period) for return periods of 50, 150, 475 and 1000 years on Class C (shallow soil) site conditions of McVerry et al. (2006). The accelerations are in units of g. Modified Mercalli Intensity (MMI) maps are shown for the same return periods. The maps are in order of PGA (a-d), 0.2 seconds spectral period (e-h), 0.5 seconds (i-l), 1 seconds (m-p), 2 seconds (q-t) and MMI (u-x). GNS Science Consultancy Report 2007/232 31

37 Figure 5b Figure 5c GNS Science Consultancy Report 2007/232 32

38 Figure 5d Figure 5e GNS Science Consultancy Report 2007/232 33

39 Figure 5f Figure 5g GNS Science Consultancy Report 2007/232 34

40 Figure 5h Figure 5i GNS Science Consultancy Report 2007/232 35

41 Figure 5j Figure 5k GNS Science Consultancy Report 2007/232 36

42 Figure 5l Figure 5m GNS Science Consultancy Report 2007/232 37

43 Figure 5n Figure 5o GNS Science Consultancy Report 2007/232 38

44 Figure 5p Figure 5q GNS Science Consultancy Report 2007/232 39

45 Figure 5r Figure 5s GNS Science Consultancy Report 2007/232 40

46 Figure 5t Figure 5u GNS Science Consultancy Report 2007/232 41

47 Figure 5v Figure 5w GNS Science Consultancy Report 2007/232 42

48 Figure 5x GNS Science Consultancy Report 2007/232 43

49 Figure 6a Deaggregation graphs to show the magnitude-distance contributions to the 475 year return period PGA at Kaikoura. GNS Science Consultancy Report 2007/232 44

50 Figure 6b Deaggregation graphs to show the magnitude-distance contributions to the 475 year return period PGA at Christchurch. GNS Science Consultancy Report 2007/232 45

51 Figure 6c Deaggregation graphs to show the magnitude-distance contributions to the 475 year return period PGA at Timaru. GNS Science Consultancy Report 2007/232 46

52 APPENDICES GNS Science Consultancy Report 2007/232 47

53 APPENDIX 1 FAULT SOURCE PARAMETERS Fault sources used as input to the PSHA. Type is slip type (ss=strike-slip, nn=normal, rv=reverse, and variants of these indicate oblique-slip), Length is predicted rupture length (km), Dip is fault plane dip (degrees), DD is dip-direction (not shown for dips of 90 degrees), Depth is to the base of the fault plane (km), Top is depth to top of the fault plane (km), SrMn is minimum slip rate (mm/yr), Sr is preferred or mean slip rate (mm/yr), and SrMx is maximum slip rate (mm/yr), W is fault plane width (km), Area is fault plane area (km 2 ), M is Moment Magnitude, Rec Int is recurrence interval (years), and ID is the fault source number that corresponds to the fault map in Figure 2. References used to update the fault sources of the 1999 report are as follows: Barnes et al., 1993, 1997, 1998a and b; Barnes, 1994a and b, 1996, 2005a and b; Barnes and Audru, 1999a and b; Barrel and Cox (in prep), Barrell et al (2002a and b, 2004), Begg and Johnston (2000), Bennett et al. (2005), Bensen et al. (2001), Berryman et al. (2002), Collot et al (1995), Estrada (2003), Forsyth (2001), Fraser (2005), Howard (2001), Howard et al (2005), Langridge et al (2003), Langridge and Berryman (2005), Litchfield et al (2003, 2004, 2005, 2006), Long et al (2003), Markeley and Tikoff (2003), Mason and Little (2006), Mason et al. (2006a and b), McFarlane and Van Dissen (2002), McVerry and Langridge (2004), Nathan et al (2002), Nicol et al (2002), Nicol and Van Dissen (2002), Norris and Cooper (2001), Norris et al. (2001), Norris and Nicholls (2004), Pace et al. (2005), Rattenbury et al. (1998, 2006), Rhoades and Van Dissen (2003), Stirling and Barnes (2003), Sutherland et al. (2006), Upton et al. (2006), Van Dissen et al. (2007), Walters et al. (2006), and Zachariasen et al. (2006). Fault Source Type Length Dip DD Depth Top SrMn Sr SrMx W Area M Rec Int ID Wairau ss Wairau (Offshore) ss Awatere (SW) ss Awatere (NE) ss Barefell Pass ss Fowlers ss Alpine (Fiord- Kelly) ss Alpine (Kelly-Tophouse) ss Clarence (SW) ss Clarence (NE) ss Clarence (Central) ss Hope (1888 rupture) ss Hope (Conway) ss Hope (Conway Offshore) ss Kekerengu-Chancet ss Jordan-Keke-Chancet rs Jordan-BKeke-Chancet rs Fidget ss Kelly ss Hope (Taramakau) ss Hope (Central-west) ss Kakapo ss Browning Pass ss Poulter ss Paparoa Range front rv Inangahua rv Maimai rv GNS Science Consultancy Report 2007/232 48

54 Brunner Anticline rv White Creek rv Lyell rv Hundalee rv Kaiwara North rv Kaiwara South rv Omihi rv Lowry rv Waitohi rv Esk rs Torlesse rv Cheesman rv Porters to Grey sr Lees Valley rs Ashley rv Springbank rv Cust rv Hororata rv Springfield rv Lk Heron-Forest Crk rv Quartz Creek rs Hutt-Peel rv Fox Peak rv Waimea South rs Waimea North rs Pisa rv Nevis rv Wairarapa-Nicholson sr Ostler rv Ahuriri River rv Irishman Creek rv Lindis Peak rs Grandview rv Cardrona South rv Cardrona North rv Blue Lake rv Dunstan rv Raggedy rv Gimmerburn rv Ranfurly rv Waipiata rv LongValley rv Hyde rv Billys Ridge rv Taieri Ridge rv Hanmer nn Ohariu South ss Wellington WHV ss Spylaw rv Blue Mountain rv Old Man rv Dry River-Huangarua rv Otaraia rv Whitemans rv GNS Science Consultancy Report 2007/232 49

55 Akatarawa-Otaki Forks sr Moonshine sr Moonlight North rs Moonlight South rs Albury rv Brothers rv Dalgety rv Dryburgh rv Hunter Range Front rv Stonewall rv Kirkliston rv Opawa rv Otematata rv Fern Gully sr Waitangi rv Pegasus 1 rv North Canterbury1 rv North Canterbury 2 rv North Canterbury 4 rv North Canterbury 11 rv North Canterbury 8 rv North Canterbury 10 rv North Canterbury 13 rv North Mernoo B0 nn North Mernoo B1 nn North Mernoo B2 nn North Mernoo 4647 nn North Mernoo E1 nn North Mernoo E2 nn North Mernoo F1 nn North Mernoo F2 nn North Mernoo 1819 nn North Mernoo K1 nn North Mernoo K2 nn North Mernoo M nn Marlborough Slope 09 rv Marlborough Slope 04 rv Marlborough Slope 08 rv Marlborough Slope 02 rv Marlborough Slope 01 rv Marlborough Slope 05 rv UpperSlope rv Marlborough Slope 06 rs E Te Rapa (segment 1-2) rs Wharanui-Campbell rs Kekerengu-Campbell rs E Needles sn Boo Boo sn Long Valley rv Kekerengu Bank rv Pukerua-Shepherds ss Waitohi rv GNS Science Consultancy Report 2007/232 50

56 APPENDIX 2 GLOSSARY Australian Plate: the tectonic plate that includes Australia and the western parts of New Zealand Active fault: a fault that has moved in historical or recent geological time Convergence: coming together of moving tectonic plates, usually resulting in mountain uplift or subduction Crust: the outermost shell of the earth Deformation: the physical alteration of the Earth s crust due to stress the process of folding, faulting, shearing, compressing or extending rocks due to tectonics Dextral slip: horizontal movement on a strike-slip fault where land on the far side of the fault moves to the right Earthquake: a sudden motion in the Earth caused by the abrupt release of accumulated stress along a fault Epicentre: the point on the Earth s surface directly above an earthquake source Extension: the pulling apart of sections of Earth s crust at faults or plate boundaries Fault: a major fracture or dislocation in the crust which has repeatedly moved in earthquakes Frequency of occurrence: the long-term average recurrence rate for earthquakes, volcanic eruptions, tsunamis, floods etc. Geodetic: relating to measurements of ground movement Geology: the study of the composition, structure and origin of Earth s rocks and minerals Geomorphology: the study of the physical features of the Earth s surface Geophysics: the study of the physical properties of the Earth [cf. geophysical; geophysicist] Grea earthquake: an earthquake of magnitude M>8.0 Ground shaking: the ground movement caused by an earthquake, also referred to as ground motion Hazard: a process that may adversely impact humankind Landslide: en mass down-slope transport, under gravity, of soil and rock material Large earthquake: an earthquake of magnitude 7.0<M<8.0 Marlborough Fault System: the system of faults connecting the Alpine Fault with the North Island Fault System Moderate earthquake: an earthquake of magnitude 5.0<M<7.0 Modified Mercalli Intensity scale: a 12 grade seismic intensity scale (1 to 12) based on observed shaking effects Magnitude: the size of an earthquake based on the original Richter scale, commonly designated e.g., M 7.0 Moment Magnitude: A magnitude computed using the scalar-seismic moment GNS Science Consultancy Report 2007/232 51

57 Normal fault: A fault that shows vertical slip in response to crustal tension Pacific Plate: the tectonic plate that includes much of the Pacific Ocean and the eastern parts of New Zealand Plate: a rigid thin segment of the Earth s the crust and upper mantle the lithosphere Recurrence interval: the average time between earthquakes Return period: the average time between ground motions, as pertain to geological hazards Reverse fault: a fault in which vertical slip occurs in response to crustal compression Risk: the likelihood of suffering adverse consequences from being exposed to a hazard Rupture: vertical and/or horizontal displacement along a fault-line Scarp: a cliff or bank formed by upward movement along a fault trace Seismicity: relating to earthquakes Seismic moment: A measure of the size of the earthquake source. It is the product of crustal rigidity, fault area, and the fault slip that accompanies an earthquake Seismology: the study of earthquakes Slip-rate: the average net rate of movement of crust along a fault Smal earthquake: an earthquake of magnitude M<5.0 Soil: All unconsolidable material above the bedrock Subduction: the process by which oceanic plates are driven down into the mantle at a convergent plate margin Tectonics: the science of plate movements and the formation of large-scale structural features Uplift: a tectonic upheaval that raises rocks from their place of formation Oblique slip: a combination of normal or reverse fault movement with strike slip Sinistral: movement on a strike-slip fault where the far side moves to the left Topography: the variation in landscape elevation with respect to sea level GNS Science Consultancy Report 2007/232 52

58 Principal Location Other Locations 1 Fairway Drive Dunedin Research Centre Wairakei Research Centre National Isotope Centre Avalon 764 Cumberland Street 114 Karetoto Road 30 Gracefield Road PO Box Private Bag 1930 Wairakei PO Box Lower Hutt Dunedin Private Bag 2000, Taupo Lower Hutt New Zealand New Zealand New Zealand New Zealand T F T F T F T F