Coseismic slip solution and preliminary postseismic results for the 7 December 2015 Mw 7.2 Sarez Lake, Tajikistan earthquake from joint inversion of Sentinel-1A and ALOS-2 InSAR data
Abstract
The 7 December, 2015, Mw 7.2 Sarez Lake earthquake occurred on the sinistral-normal, NNE striking Sarez-Karakul fault system, situated in the Gorno-Badakhshan Autonomous region of Tajikistan, in the central Pamir. Previous geodetic investigations suggest that the region accommodates pure-shear deformation with N-S compression and E-W extension. We study the coseismic and postseismic phases of the deformation associated with this event using S1A and ALOS-2 SAR data, complemented by Landsat-8 images for constraining the fault geometry. InSAR data was processed with the ISCE software and interferograms were phase unwrapped conservatively using the branch-cut algorithm, where manual cuts and bridges were added to retrieve most of the coherent phase in the highly deformed region near the fault. We invert the coseismic interferograms to solve for the fault dip angle, slip, and rake using a Bayesian inversion method based on a Markov chain Monte Carlo sampling of the parameter space. Our model includes 3 segments (each divided into 5x5 km2 patches) following the trace inferred from InSAR fringe patterns and horizontal shifts obtained by image correlation of pre- and post-mainshock Landsat-8 images. The solution shows that the fault is near-vertical and the slip mostly left-lateral, consistent with the centroid moment tensor. Most of the moment is released along the fault section that extends 25 km NE from the epicenter and down to a depth of 12 km. A secondary patch of slip occurs at a larger depth on the central segment where the fault makes a right-step in the Karakul Valley. Building postseismic InSAR time series will help us understand postseismic relaxation processes and the lithospheric rheology of the Pamir. Extreme relief and abundant snow cover require careful processing to mitigate the signal due to the tropospheric phase delay and unwrapping errors. We use global weather models to estimate the interferometric phase delay produced by tropospheric variability. Specifically, we compare time series built using tropospheric corrections derived from the ERA-Interim, MERRA-1, and MERRA-2 weather models. Postseismic surface deformation time series will be presented.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFM.G22A..07S
- Keywords:
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- 1240 Satellite geodesy: results;
- GEODESY AND GRAVITYDE: 1241 Satellite geodesy: technical issues;
- GEODESY AND GRAVITYDE: 7215 Earthquake source observations;
- SEISMOLOGYDE: 8419 Volcano monitoring;
- VOLCANOLOGY