1. California Institute of Technology
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

2. Seismotectonic Context
Mww moment tensor P T

3. Unusual Moment Tensor P T
Characteristics of focal mechanisms of shallow (0-30km) earthquakes (Celerier, 2008)

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

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

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

7. Strike-parallel
Strike-perpendicular

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

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

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

11. 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
Meyer–Yamada wavelet.
The MYM is an orthonormal base.
完备正交基，小波原子
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)

12. Finite Source Model

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

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

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

16. Effect on the Makran megathrust and Chaman Fault system
1945
1765
Coulomb Stress Change on Makran Megathrust
Coulomb Stress Change on NS strike-slip faults

17. Conclusion
Rupture initiated at the southern tip of the Chaman Fault and propagated along the Hosbah fault within the Makran accretionnary 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?

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

20. (Szeliga et al, JGR, 2012)

21. (Szeliga et al, JGR, 2012)