Deriving Centimeter-Level Coseismic Deformation and Fault Geometries of Small-To-Moderate Earthquakes From Time-Series Sentinel-1 SAR Images

Heng Luo,Shengji Wei,Teng Wang,Mingsheng Liao,Jianya Gong

doi:10.3389/feart.2021.636398

Abstract

Small-to-moderate earthquakes (e.g. ≤Mw5.5) occur much more frequently than large ones (e.g. &gt;Mw6.0), yet are difficult to study with InSAR due to their weak surface deformation that are severely contaminated by atmospheric delays. Here we propose a stacking method using time-series SAR images that can effectively suppress atmospheric phase screens and extract weak coseismic deformation in centimeter to sub-centimeter level. Using this method, we successfully derive coseismic surface deformations for three small-to-moderate (Mw∼5) earthquakes in Tibet Plateau and Tienshan region from time-series Sentinel-1 SAR images, with peak line-of-sight deformation ranging from 5–6 mm to 13 mm. We also propose a strategy to downsample interferograms with weak deformation signal based on quadtree mesh obtained from preliminary slip model. With the downsampled datasets, we invert for the centroid locations, fault geometries and slips of these events. Our results demonstrate the potential of using time-series InSAR images to enrich earthquake catalog with geodetic observations for further study of earthquake cycle and active tectonics.

Highlights

Surface deformations produced by shallow earthquakes have been widely studied by Interferometric Synthetic Aperture Radar (InSAR) since the 1992 Landers earthquake (Massonnet et al, 1993)
To demonstrate the capability of our method in extracting small coseismic deformation signal, we show a representative application to the 2017/09/16 Mw5.5 Kuche earthquake (Figure 2)
According to global catalogs (e.g. U.S Geological Survey (USGS), Global Centroid Moment Tensor (GCMT)), they are: the September 16, 2017 Mw5.5 Kuche thrust-faulting earthquake occurred in the south margin of Tienshan; the December 4, 2016 Mw5.2 Nierong strike-slip earthquake occurred in central Tibet Plateau, and the February 1, 2017 Mw5.2 Zhongba normal-faulting earthquake occurred in southern Tibet Plateau

Summary

INTRODUCTION

Surface deformations produced by shallow earthquakes have been widely studied by Interferometric Synthetic Aperture Radar (InSAR) since the 1992 Landers earthquake (Massonnet et al, 1993). We successfully retrieve coseismic deformations for three earthquakes with magnitudes from Mw5.2 to 5.5 in Tibet region by applying a stacking method using time-series SAR images (Figure 1) These three representative events have thrust, strike-slip and normal faulting mechanisms, respectively. To demonstrate the capability of our method in extracting small coseismic deformation signal, we show a representative application to the 2017/09/16 Mw5.5 Kuche earthquake (Figure 2) For this earthquake, we collect 37 and 36 Sentinel-1 SAR images from the ascending track AT12 and descending track DT165, respectively. In the stacked InSAR interferograms that cover the earthquake, atmospheric turbulence from the reference images are dominating the data where the coseismic deformation signals are hardly visible due to their weaker amplitudes (Figures 2B,E). We fix the initial strike and/or dip angles based on the focal mechanisms from reputed earthquake catalogs (e.g. USGS or GCMT) and perform the source inversion to obtain the optimal location, depth and slip vector

RESULTS

DISCUSSION AND CONCLUSION

DATA AVAILABILITY STATEMENT