Mapping the Tyrrhenian and Adriatic Mohos across the northern and central Apennine chain through teleseismic receiver functions

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1 Mapping the Tyrrhenian and Adriatic Mohos across the northern and central Apennine chain through teleseismic receiver functions Giuliana Mele Istituto Nazionale di Geofisica e Vulcanologia - Roma, Italy giuliana.mele@ingv.it

local: < 100 km (shallow crust) regional: 100-1,400 km (1-13 ) (crust) upper mantle: 13-30 (upper mantle) teleseismic: > 30 (lower mantle and core) Seismic waves provide

2 local: < 100 km (shallow crust) regional: 100-1,400 km (1-13 ) (crust) upper mantle: (upper mantle) teleseismic: > 30 (lower mantle and core) Seismic waves provide our most effective probe of Earth s interior, and they constitute the main method of collecting data upon which we base our present concepts of Earth s internal structure.

time series computed from three-component recordings of eqs occurring at distances > 30 used by seismologists to determine the depth of a velocity contrast (seismic discontinuity) beneath a

3 time series computed from three-component recordings of eqs occurring at distances > 30 used by seismologists to determine the depth of a velocity contrast (seismic discontinuity) beneath a seismometer through the identification of P-to-S converted waves geometry of ray paths receiver function incoming teleseismic compressional (P) waves convert to shear (S) waves at the velocity contrast Ps and later reverberations/conversions have much larger amplitude on the horizontal radial direction (i.e. along the great circle connecting source to receiver). Deconvolution of the vertical from the horizontal component (rotated to radial) produces the so-called receiver function that is a simpler waveform where most of the unwanted source (rupture kinematics, near-source structure) and propagation path effects are removed to enhance Ps conversions (near-receiver effects) [Langston, 1979].

4 the delay of the converted Ps with respect to the direct P (t Ps-P ) depends on: H = t Ps-P / ((1/Vs 2 -p 2 ) 1/2 - (1/Vp 2 -p 2 ) 1/2 ) depth of the velocity contrast velocity structure in the layer between the velocity contrast and the Earth s surface incidence angle of the P wave (expressed through the ray parameter p=1/v. sin i) The most significant PS conversions that are observed in a t.r.f. are those generated at the Moho and at the 410- and 660-km boundaries (larger velocity contrast): t Ps-P Moho ~ 4 s t Ps-P 410-km ~ 40 s t Ps-P 660-km ~ 65 s

0 iii) all depths n. of eqs Japan, Kuril, Kamchatka, Sumatra, Aleutian, Taiwan n.

5 i) teleseismic distance limited to ~ 90 (beyond this distance, the direct phases become complicated due to interactions with the outer core) ii) magnitude > 5.0 iii) all depths n. of eqs Japan, Kuril, Kamchatka, Sumatra, Aleutian, Taiwan n. of eqs Azimuthal projection (centered on Italy) of the earthquakes used to compute receiver functions

6 intermediate and deep-focus eqs OR shallow eqs with simple rupture mechanism and crustal structure crust upper mantle lower mantle outer core inner core

7 D=9,360 km baz=28 - evdp=23 km - Mw=6.1 receiver function P Ps

8 GeoModAp Project : regional arrays of 3-D stations Po plain (Amato et al. 1998) x giu-ott 1994 Adriatic Sea x x x apr-lug 1995 apr-nov 1996 Tyrrhenian Sea

Cassinis, R., Scarascia, S., Lozej, A., 2003.

$from seismic refraction data. A new synthesis. Boll. Soc.$

9 Cassinis, R., Scarascia, S., Lozej, A., The deep crustal structure of Italy and surroundings areas from seismic refraction data. A new synthesis. Boll. Soc. Geol. It. 122, Moho depths larger than 40 km in the Apennine range

10 Tiberina v. 50 km profile of stacks of radial r.f. (NE quadrant; 80 ±10 ) x Tuscany x Ps P early Ps Moho arrivals beneath the Elba island and Tuscany as far as the Tiberina valley larger Ps Moho -P beneath the stations of the eastern part of the array, progressively more delayed from the Adriatic coast toward the Apennines double conversion beneath the central portion of the array corresponding to the Tiberina valley time-todepth crustal Vp ±0.2* km/s and Poisson's ratio**=0.25 (Zandt & Ammon, 1995) *a variation of ± 0.2 km/s in Vp affects the estimate of Moho depth of less than 1 km **s = 1/2 (V P 2-2V S 2 ) / (V P 2 - V S 2 ) / Vp=7.9 km/s beneath the Elba island and Tuscany the crust-mantle boundary is shallow (20 to 24 km) the double Ps conversion beneath the Val Tiberina graben is interpreted with the overlapping of the Tuscan/peri-Tyrrhenian Moho (20 km) above the Adriatic Moho. The depth of the lower discontinuity is computed assuming, between the two velocity contrasts, Vp= 7.9 km/s, that is the velocity estimated for the Tyrrhenian uppermost mantle by Mele et al. (1998) 52 km from the Adriatic coast toward the Apennines, Moho deepens from 28 to 52 km

11 profile of stacks of radial r.f. (NE quadrant; 80 ±10 ) Tremiti Is. 50 km x Apennines x x x x x as across northern Apennines, Ps arrivals are earlier in the western part of the array than in the eastern part. From both sides Ps-P increases toward the chain time-todepth Moho is shallower (22 km) beneath the Tyrrhenian side of Italy and deepens to km toward the E. Larger Moho depths (down to 45 km) correspond to the higher topography area, while in the foreland area (Adriatic Sea) crust is 32 km thick

13 PpPs PpSs+PsPs Moho depth ~ 40 km t (Ps-P) = 4.9 s 42 km slant stacking technique of Zhu & Kanamori (2000)

14 Tuscany 100 km Mele & Sandvol, EPSL (2003) 40 local and average values Mele, Cavinato & Sandvol, EPSL (2006) Di Luzio, Mele, Tiberti, Cavinato & Parotto, EPSL (2009)

15 Mele & Sandvol 2003 Mele et al Di Luzio et al Tyrrhenian Moho (Cassinis et al. 2003) 4 0 r.f. are consistent with the interpretation of active seismic data in the western part of the arrays and along the Adriatic coast; there is no agreement along the Apennines where Moho is deeper both beneath the northern and central Apennines

16 + permanent stations of the Italian Seismic Network CROP03 CROP11 DSS Mele & Di Luzio, in preparation

CROP11 DSS The Fonteviva 1 well is located 60 km west of the Adriatic coast. It drilled the Apulian Platform, belonging to the Adriatic crust, beneath a 2.

17 CROP11 DSS The Fonteviva 1 well is located 60 km west of the Adriatic coast. It drilled the Apulian Platform, belonging to the Adriatic crust, beneath a 2.1 km-thick thrust pile. We therefore assign station MIDA to the Adriatic crust to interpolate depth values and reconstruct the Adriatic Moho Mele & Di Luzio, in preparation

24 Mele et al., 2003 [34] Piana- Agostinetti, Lucente, Selvaggi, Di Bona, GRL, 2002 [35] Levin, Margheriti, Park, Amato, GRL, 2002

MOHO DEPTH AND CRUSTAL STRUCTURE IN PENINSULAR ITALY

MOHO DEPTH AND CRUSTAL STRUCTURE IN PENINSULAR ITALY Neutrino Geoscience 2010 Alessandro Amato Istituto Nazionale di Geofisica e Vulcanologia Talk outline Italy: tectonic setting and deep structures Moho