Optimization of InSAR based coseismic slip modeling for moderate earthquakes accounting for fore–aftershock sequence

Abstract

Determination of coseismic slip distribution for moderate (moment magnitude, Mw≤ 6.5) earthquakes is challenging as the commonly-used interferometric synthetic aperture radar (InSAR) technique is unable to separate mainshock and fore–aftershocks due to its limited temporal resolution. In this study, we propose a new method of optimizing coseismic slip modeling by removing fore–aftershock contributions using earthquake relocation data and empirical earthquake source scaling relationships. The method is tested with a series of synthetic fore–main–aftershock sequences, through which we demonstrate that our method can largely recover the real slip distribution of the mainshock. The synthetic tests show that if the moment release by fore–aftershocks is ≥10% of the mainshock moment release, fore–aftershock corrections are necessary to improve the accuracy of coseismic slip model. We also test the proposed method with the 2021 Mw 6.3 northern Thessaly, Greece earthquake sequence, in which case we have independent InSAR measurements for both the mainshock and aftershocks. We successfully obtain the slip distribution of the mainshock from the main–aftershock-mixed InSAR measurements, and the result is highly consistent with that derived from the mainshock-only InSAR data. We also evaluate the robustness of the method using the northern Thessaly sequence through a series of tests, showing that the proposed method makes significant improvements even if the earthquake relocation error reaches 5 km. In the end, we apply the method to re-investigate the 2021 Mw 6.0 Yangbi earthquake sequence and find that previous studies may have overestimated the coseismic slip by 25% and the total seismic moment by 18%.