The 2013, Mw 7.7 Balochistan earthquake, energetic strike-slip reactivation of a thrust fault

We analyse the Mw 7.7 Balochistan earthquake of 09/24/2013 based on ground surface deformation measured from sub-pixel correlation of Landsat-8 images, combined with back-projection and finite source modeling of teleseismic waveforms. The earthquake nucleated south of the Chaman strike-slip fault an...

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Bibliographic Details
Published in:Earth and planetary science letters 2014-04, Vol.391, p.128-134
Main Authors: Avouac, Jean-Philippe, Ayoub, Francois, Wei, Shengji, Ampuero, Jean-Paul, Meng, Lingsen, Leprince, Sebastien, Jolivet, Romain, Duputel, Zacharie, Helmberger, Don
Format: Article
Language:English
Subjects:
Balochistan earthquake
Chaman fault
Dynamic mechanical properties
Dynamics
earthquake source model
Faults
Geological faults
image geodesy
Makran megathrust
Mathematical analysis
Rupture
Seismic phenomena
Slip
Thrust
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Summary:We analyse the Mw 7.7 Balochistan earthquake of 09/24/2013 based on ground surface deformation measured from sub-pixel correlation of Landsat-8 images, combined with back-projection and finite source modeling of teleseismic waveforms. The earthquake nucleated south of the Chaman strike-slip fault and propagated southwestward along the Hoshab fault at the front of the Kech Band. The rupture was mostly unilateral, propagated at 3 km/s on average and produced a 200 km surface fault trace with purely strike-slip displacement peaking to 10 m and averaging around 6 m. The finite source model shows that slip was maximum near the surface. Although the Hoshab fault is dipping by 45° to the North, in accordance with its origin as a thrust fault within the Makran accretionary prism, slip was nearly purely strike-slip during that earthquake. Large seismic slip on such a non-optimally oriented fault was enhanced possibly due to the influence of the free surface on dynamic stresses or to particular properties of the fault zone allowing for strong dynamic weakening. Strike-slip faulting on thrust fault within the eastern Makran is interpreted as due to eastward extrusion of the accretionary prism as it bulges out over the Indian plate. Portions of the Makran megathrust, some thrust faults in the Kirthar range and strike-slip faults within the Chaman fault system have been brought closer to failure by this earthquake. Aftershocks cluster within the Chaman fault system north of the epicenter, opposite to the direction of rupture propagation. By contrast, few aftershocks were detected in the area of maximum moment release. In this example, aftershocks cannot be used to infer earthquake characteristics. •The Mw 7.7 Balochistan earthquake reactivated a thrust fault with purely strike-slip motion.•Seismic rupture was boosted, not impeded, as it propagated on non-optimally oriented fault.•Aftershocks don't delineate rupture area and cluster north of epicenter opposite to the rupture directivity.•No shallow slip deficit; maximum slip occurred at the surface.
ISSN:0012-821X
1385-013X
DOI:10.1016/j.epsl.2014.01.036