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Source solution of the 2015 Mw 7.2 Murghab, Tajikistan earthquake from InSAR and seismological data

Combining space-based geodetic and array seismology observations can provide detailed informations about earthquake ruptures in remote regions. Here we use Landsat-8 imagery and ALOS-2 and Sentinel-1 radar interferometry data combined with data from the European Seismology Network (EU) to describe the source of the December 7, 2015, Mw7.2 Mughrab (Tajikistan) earthquake. The earthquake reactivated a 70 km-long section of the Serez-Karakul fault, a NE oriented sinistral, trans-tensional fault in northern Pamir. Pixel offset data delineate the geometry of the surface break and line of sight ground shifts from two descending and three ascending interferograms constrained the fault dip and slip solution. Two right-stepping, NE-striking segments connected by a more easterly oriented segment, sub-vertical or steeply dipping to the west were involved. The solution shows two main patches of slip with up to 3.5 m of left lateral slip on the southern and central fault segments. The northern segment has a left-lateral and normal oblique slip of up to a meter. Back protection of the high frequency (0.5-2.0 s) band of seismic data recorded by the EU network processed using the Multitaper-MUSIC approach focus sharply along the modeled fault. The time progression of the high frequency radiators shows that, after a 10 seconds initiation phase at slow speed, the rupture progressed in 2 phases at super-shear velocity (~6 km/s) separated by a ~10 seconds interval of slower propagation corresponding to the passage through the restraining bend. The intensity of the high frequency radiation reaches maxima during the early and middle phases of slow propagation and is reduced by ~50% during the super-shear phases of the propagation. These findings are consistent with other studies on other strike-slip faults in continental domain, showing the importance of the fault geometric complexities in controlling the speed of fault propagation and related high frequency radiation pattern.