Using InSAR for evaluating the accuracy of locations and focal mechanism solutions of local earthquake catalogues

Abstract

SUMMARYEarthquake source parameters play a fundamental role in evaluating seismic hazard. In many countries, the relatively low accuracy of the earthquake source parameters owing to sparse seismic monitoring networks prevents accurate seismic hazard evaluation. Interferometric Synthetic Aperture Radar (InSAR) is a useful tool for accurate fault parameter determination of shallow inland earthquakes. We compared the fault parameters (location and rupture geometry) derived from InSAR with those derived from local and global seismic data to assess the credibility of the earthquake catalogues. We set our targets to Iran and Japan, where seismic networks are relatively sparse and dense, respectively, and analysed a total of 10 shallow inland earthquakes. To compare the fault parameters for each studied earthquake, we first created interferograms using InSAR data from multiple satellites and conducted fault model inversions assuming uniform slip on a rectangular finite fault. For the studied Iranian earthquakes, the epicentres of the United States Geological Survey (USGS) catalogue were more consistent with the InSAR-derived fault model compared to those of the local catalogue of the Iranian Seismological Center (IRSC). For the studied Japanese earthquakes, the epicentres of the Japan Meteorological Agency (JMA) catalogue were more consistent with the InSAR-derived fault model compared to those of the USGS. Assuming that the accuracy of the USGS locations is comparable for the two countries, the JMA catalogue has a higher accuracy than the IRSC catalogue. The difference in the accuracy for the two local catalogues can be explained by the larger azimuthal gaps of the IRSC seismic network. We also showed that the IRSC- and JMA-derived centroids were more consistent with the InSAR-derived fault model compared to those of the Global Centroid Moment Tensor (GCMT) catalogue. The focal mechanism solutions derived from InSAR and seismic CMT solutions were significantly different, highlighting the difficulties in determining the focal mechanism parameters from seismic data, even when the seismic station coverage is dense. As InSAR data can be easily accessed, this study presents a cost-effective method to assess and improve the accuracy of the local earthquake catalogues anywhere in the world.