Stress-Drop Scaling of the 2016 Gyeongju and 2017 Pohang Earthquake Sequences Using Coda-Based Methods

Abstract

ABSTRACT Two M 5 earthquakes struck the southeastern Korean Peninsula in September 2016 and November 2017, causing damage near the epicentral areas. We analyze the stress-drop scaling of these two earthquake sequences using coda-based methods and Bayesian inversion. The 2016 Gyeongju earthquake sequence is a typical earthquake sequence generated by tectonic processes. In contrast, the 2017 Pohang earthquake sequence is believed to be related to fluid injections conducted for the development of enhanced geothermal systems. As the two sequences occurred in the same tectonic regime, our study provides a good opportunity to compare the stress-drop scaling between a tectonic earthquake sequence and an earthquake sequence influenced by fluid injections. We found that the stress drops of events in the Pohang sequence are lower than those of the Gyeongju sequence with similar magnitude. Although it is likely that this difference results from focal depth variations, a reduction of stress drop due to fluid injections cannot be ruled out.