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A Study of Faulting Near Dushanbe (Tajikistan) from Time Series InSAR and Tectonic Geomorphology

Session: Modern Geodesy for Observation and Its Modeling of Earthquake Deformation

Type: Oral

Date: 4/19/2021

Presentation Time: 05:45 PM Pacific

Description: 

Dushanbe (capital city of Tajikistan) sits at the northern margin of the Afghan-Tajik depression, a sedimentary basin bounded by the Tian Shan, Pamir, Hindu Kush and Afghan platform. A set of north-south trending anticlines sweep up the basin’s interior and merge along the northern margin into the right-lateral Ilyak fault, immediately south of Dushanbe. A GPS analysis from Metzger et al., 2020 suggests the Ilyak fault accommodates ~5mm/yr of shortening and 8-15mm/yr of strike slip deformation. The 1989 MLH 5.5 Gissar earthquake and a number of others (1953, 1968) occurred close to the western end of the Ilyak fault, but the exact faults they ruptured have not been identified. To the south of Dushanbe, sharp GPS velocity gradients across basin anticlines hint at localisation of strain and may indicate creep on the associated thrusts. However, sparse GPS data alone are insufficient to determine the extent to which the Ilyak fault or basin thrusts are locked or slipping aseismically.

In this study we combine high resolution mapping of the interseismic deformation from InSAR with detailed mapping of quaternary deformation using satellite-derived DEMs to gain a better understanding of the distribution and potential seismic or aseismic behaviour of active faults in the region. We apply a multi-temporal InSAR time series analysis over a ~5 year period using the New Small Baselines Subset (NSBAS) processing chain with data from ESA’s Sentinel-1. The resulting line-of-sight velocity maps provide a continuous view of the rate of deformation across the basin. We find a sharp step in velocity across the Ilyak fault extending ~60 km along strike, implying it is creeping at shallow depths. We also observe shallow creep on the Bobotag thrust, which lies at the base of an anticline extending into the basin directly southwest of Dushanbe. Past earthquakes show that fault segments within the Ilyak fault zone are capable of producing damaging earthquakes. We use DEMs to delineate previously unmapped faults, which may constitute sources of hazard, from their expression in the geomorphology.

Presenting Author: Roberta Wilkinson

Student Presenter: Yes

Authors