Dr Roberta Wilkinson

Abstract:

Plain Language Summary: Tajikistan is prone to earthquakes and landsliding, both within the mountainous regions and in surrounding valleys, such as the wide basin in which the capital city of Dushanbe is situated. The major Ilyak active fault is mapped within this basin, and yet relatively few large earthquakes have been recorded in the area. We use satellite radar interferometry to image ground deformation in the region around Dushanbe. We show that the Ilyak fault is actually creeping at the surface, and so not storing up slip to be released in occasional earthquakes. This creep behavior is likely caused by the weak sedimentary rocks through which the fault runs. However, earthquakes that have occurred at depth beneath the creeping part of the fault and other potentially active faults in the vicinity both indicate ongoing earthquake hazard. Our surface rate maps also highlight widespread down‐slope ground movement in slow landslides, offering a means of identifying and monitoring these hazards.

Abstract:

The study of surface ruptures is key to understanding the earthquake occurrence of faults especially in the absence of historical events. We present a detailed analysis of geomorphic displacements along the Dzhungarian Fault, which straddles the border of China and Kazakhstan. We use digital elevation models derived from structure-from-motion analysis of Pléiades satellite imagery and drone imagery from specific field sites to measure surface offsets. We provide direct age constraints from alluvial terraces displaced by faulting and indirect dating from morphological analysis of the scarps. We find that the southern 250 km of the fault likely ruptured in a single event in the last 4000 years, with displacements of 10-15 m, and potentially up to 20 m at one site. We infer that this Dzhungarian rupture is likely linked with a previously identified paleo-earthquake rupture on the Lepsy Fault through a system of splays in the intervening highlands. Though there are remaining uncertainties regarding consistency in age constraints between the two fault ruptures, most of the sites along the two faults are consistent with a most recent event 2000-4000 years ago. Rupture on the Dzhungarian Fault alone is likely to have exceeded Mw 8, and the combined Lepsy-Dzhungarian rupture scenario may have been up to Mw 8.4. Despite being at the upper end of known or inferred continental earthquake magnitudes, our proposed scenario combining the 375 km of the Dzhungarian and Lepsy ruptures yields a slip-to-length ratio consistent with global averages and so do other historical intra-continental earthquakes in Central Asia.