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The Sept, 24, 2013 , Mw7.7 Balochistan Earthquake

The Sept, 24, 2013 , Mw7.7 Balochistan Earthquake. J.P. Avouac , F. Ayoub , S. Wei, J.P. Ampuero , L. Meng, S. Leprince , R. Jolivet, Z. Duputel and D. Helmberger California Institute of Technology. Seismotectonic Context. Mww moment tensor. P. T. Landsat-8 images:

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The Sept, 24, 2013 , Mw7.7 Balochistan Earthquake

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  1. The Sept, 24, 2013, Mw7.7 BalochistanEarthquake J.P. Avouac, F. Ayoub, S. Wei, J.P. Ampuero, L. Meng, S. Leprince, R. Jolivet, Z. Duputel and D. Helmberger California Institute of Technology

  2. Seismotectonic Context Mww moment tensor P T

  3. Landsat-8 images: • USGS website • Pre-earthquake images September, 10, 2013 (14 day before) • Post-earthquake images September, 26, 2013 (2 days after)

  4. Image Processing (COSI-Corr) (Leprince et al, 2007)

  5. Measured Surface Displacement Field • Window size : 64x64 pixels (960x960 m) • Step (GSD of displacement maps): 16 pixels (240 m) • 1-suncertainly: 30 cm - Amplitude of NS component - Horizontal displacement vector field

  6. Strike-parallel Strike-perpendicular

  7. The rupture falls on the Hosbah fault along the front of the Kech Band Kech Band (Lawrence, Kahn,Dejong, Farah and Yeats, 1981)

  8. Rupture kinematics from backprojection of Teleseismic waveforms • Data: Japanese Hi-net seismic network • Multitaper-MUSIC array processing technique (Meng et al, 2011) • Frequency band: 0.5-2Hz • HF source duration: 50s

  9. Rupture kinematics from backprojection of Teleseismic waveforms Backprojectionof teleseismic waveforms (Hi-NET), 0.5-2Hz

  10. Finite Source Model Forward modeling: (assumes a pulse-like source) NB: Green’s functions are calculated with a crustal layered structure in the source region, then use ray theory to propagate to the receiver Inversion: A simulated annealing algorithm is used to simultaneously invert for the slip, rise time and rupture velocity (Ji, C., D. J. Wald and D. V. Helmberger, 2002a.b, BSSA)

  11. Finite Source Model

  12. Rupture depth <12km, No shallow slip deficit (Fialko et al, 2005)

  13. Comparison with interseismic strain PANG PANG- BEDI BEDI GPS velocities relative to India (Szeliga et al, JGR, 2012)

  14. Long Term Tectonics Strike slip motion along the Hosbah fault potentially enhanced by eastward extrusion of easternmost outer Makran prism

  15. Effect on the Makranmegathrust and Chaman Fault system 1765 1945 Coulomb Stress Change on MakranMegathrust Coulomb Stress Change on NS strike-slip faults

  16. Conclusion • Rupture initiated at the southern tip of the Chaman Fault and propagated along the Hosbah fault within the Makranaccretionnary prism • Large strike-slip motion (6m on average, along 200km long fault trace, 0-12km depth) on pre-existing thrust fault • Strike-slip enhanced due to eastward squeezing of Makran prims • No shallow slip deficit • Large rupture velocity on misoriented fault • Rupture failed to propagate along the Chaman fault (despite most aftershocks there). Effect of shallow dip angle? shallow creep? unloading due to 1935 EQ?

  17. Seismotectonic Context Mww moment tensor P T (Szeliga et al, JGR, 2012)

  18. (Szeliga et al, JGR, 2012)

  19. (Szeliga et al, JGR, 2012)

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