FROM DRAWING ANTICLINE AXES TO 3D MODELLING OF SEISMOGENIC SOURCES: EVOLUTION OF SEISMOTECTONIC MAPPING IN THE PO PLAIN

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1 FROM DRAWING ANTICLINE AXES TO 3D MODELLING OF SEISMOGENIC SOURCES: EVOLUTION OF SEISMOTECTONIC MAPPING IN THE PO PLAIN Burrato P.*, Maesano F. E. *, D Ambrogi C.**, Toscani G., Valensise G.* (*) INGV, Istituto Nazionale di Geofisica e Vulcanologia, pierfrancesco.burrato@ingv.it; framae80@gmail.com; gianluca.valensise@ingv.it (**) ISPRA, Servizio Geologico d Italia/Dipartimento Difesa del Suolo, chiara.dambrogi@isprambiente.it ( ) Dipartimento di Scienze della Terra, Università di Pavia, toscani@dst.unipv.it

2 THE PROBLEM The Po Plain is a challenging area for active tectonics studies. In this almost flat region: Hence: Strain rates are low; Seismicity is moderate and infrequent; Regional tectonic signal is larger than local ones; Sedimentary rates are much higher than tectonic ones; Locally, large man-induced vertical ground motion. Faulting and folding is is almost everywhere blind. To identify and characterize Seismogenic Sources we need an approach that integrates morphotectonic analysis and (possibly) high resolution subsurface geological and geophysical datasets.

3 ACTIVE DEFORMATION: GPS GPS velocities not able to capture the activity of the outer blind thrust fronts! May-June 2012 Emilia seismic sequence (M ) Bennett et al., 2012 Active shortening localized along the mountain front

4 HISTORICAL AND INSTRUMENTAL SEISMICITY January 24, 25 and M 4.2, 4.9 and 5.4 Mw May-June 2012 seismic sequence M 5.9 and 5.8 CPTI ISIDe - Catalogo della Sismicità Italiana -

5 REGIONAL vs LOCAL TECTONIC SIGNAL Regional subsidence due to NA mountain building Blind faulting and folding Fantoni & Franciosi, 2010

6 DRAWING ANTICLINE AXES Desio, 1965

7 ACTIVE FAULTS AND THEIR GEOMORPHOLOGICAL EVIDENCE Castaldini & Panizza, 1991 Castaldini & Panizza, 1988 Active faults mostly concentrated in the mountain areas

8 BUILDING A SEISMOGENIC SOURCE MODEL Input: subsurface geological and geophysical data MILANO VENEZIA BOLOGNA Bigi et al., 1992 Modello Strutturale d Italia

9 BUILDING A SEISMOGENIC SOURCE MODEL Input: subsurface geological and geophysical data MILANO VENEZIA BOLOGNA Bigi et al., 1992 Modello Strutturale d Italia AA.VV.

10 BUILDING A SEISMOGENIC SOURCE MODEL Input: geomorphology and near-surface geological data Trino Vercellese 2- San Colombano 3- Romanengo 4- Monte Netto-Castenedolo- Ciliverghe Burrato et al., 2003

11 FROM GEOLOGICAL/GEOMORPHOLOGICAL DATA TO SEISMOGENIC SOURCES DISS v GIS based database Web interface Google Earth

12 THE EMILIA SEISMIC SEQUENCE May 2012 (Mmax 5.9) 29 May-13 June 2012 (Mmax 5.8) B FERRARA REGGIO EMILIA RAVENNA A CPTI ISIDe - DISS -

13 THE EMILIA SEISMIC SEQUENCE Mirandola Anticline Ferrara Anticline 1? 2 Carminati et al., 2010

14 COSEISMIC SURFACE DISPLACEMENT SAR image from:

15 DRAINAGE EVOLUTION IN THE EMILIA PLAIN Po River before VIII century b.c. Secchia River XII-XV century A.D. Panaro River Reconstruction based on Castaldini et al. (1979) Burrato et al., 2003

16 DRAINAGE ANOMALIES IN THE EMILIA PLAIN Contour-lines (5m) Topographic gradient Avg drainage direction >15 Anomalous reach > base map from: Geomorphological Map of the Po Plain (1997) Burrato et al., 2003

17 GROWTH STRATA ACROSS THE MIRANDOLA ANTICLINE Topography thickening 0.40 My A thinning Growth strata 0.65 My B Horizon A Meters My C Horizon B Horizon C 0.40 My 0.65 My 3.60 My S N Burrato et al., Meters

18 DISLOCATION MODELING Vertical displacement for 1 km of slip Po River Mirandola Source Length 18 km Width 14 km Min depth 6 km Max depth 12 km Strike N100 Dip 25 Rake 90 Max M Secchia River - Panaro River 20 km Burrato et al., 2003

19 CALCULATING SLIP RATE USING DISLOCATION MODELING m x 1000 m slip Expected Vertical displacement Meters m x 670 m of slip in 400 Ky on a 25 dipping fault Topography Horizon A Horizon B S 1.68 mm/y Horizon C 0.40 My 0.65 My 3.60 My Meters N Burrato et al., 2003

20 REFINING SR CALCULATIONS USING HIGH RESOLUTION DATA Scrocca et al., 2007 Mirandola anticline Uplift rate since Pleistocene 1.70 mm/a without considering differential compaction Burrato et al., mm/a using a decompaction workflow Scrocca et al., 2007

21 A NEW APPROACH: FROM RAW DATA TO SR Fault propagation folds: trishear Dataset 3D models Dislocated horizons: fault parallel flow Decompaction Shallow surfaces: Dislocation modeling Maesano et al., GeoItalia

22 DATASET Regional cross sections Shallow sections CARG Project-RER Sections modified from: Fantoni et al., 2009 Toscani et al., 2006 Maesano et al., GeoItalia

23 CONSTRUCTION OF 3D MODELS FROM 2D SECTIONS Maesano et al., GeoItalia

24 DECOMPACTION 10% thickness changes at anticline axes Up to 40% thickness changes in synclines Maesano et al., GeoItalia

25 RESULTS 3 2,5 Slip rates corrected for differential compaction Emilia Folds Ferrara Folds Romagna Folds 3.6 Differential slip rates (mm/y) 2 1,5 1 0, Age (My) sect 1 sect 2 sect 3 sect 4 Regional cross sections from W to E Maesano et al., GeoItalia