Source parameters and locations of the 1949 Mw7.4 Khait and 1907 Mw7.6 Karatag earthquakes: implications for how mountain ranges collide

The 1949 M_w7.4 Khait and 1907 M_w7.6 Karatag earthquakes are the two largest earthquakes of the last ~100 years within Tajikistan, in a zone of convergence between the Pamir and Tian Shan ranges at a rate of ~1cm/yr. The historical nature of these events means seismological and geodetic data are lacking. As such, their locations and source parameters have been very uncertain – preventing our understanding of how they fit into the tectonic model of the north-western Pamir.  

Here we present calibrated earthquake relocations for the 1949 earthquake and focal mechanisms determined from digitised seismograms for the 1949 and 1907 earthquakes. We also present a catalog of precise relocations for moderate magnitude earthquakes from 1949 to the present in vicinity of the Vakhsh Thrust. Finally, we present earthquake surface rupture mapping from the Vakhsh Valley, determined from ultra-high resolution elevation models derived from satellite stereo-imagery.  

We find that the 1949 Khait earthquake did not occur on the Vakhsh Fault, a major right-lateral fault that bounds the northern margin of the Pamir, as previously thought. Instead it occurred on an unmapped fault in the Tian Shan basement. However, 10-20m scarps observed on the south Vakhsh valley show this fault is capable of producing large earthquakes. This tells us the Pamir–Tian Shan convergence is distributed across several basement faults capable of producing large earthquakes. It also tells us that the largest earthquakes may occur on faults which may appear minor in the landscape, which has implications for seismic hazard in the region.