Source Properties of Repeating Earthquakes in Aftershocks of the 2016 ML 5.8 Gyeongju Earthquake Sequences

Date: 4/25/2019

Time: 06:00 PM

Room: Fifth Avenue

Repeating earthquakes (REs) represent characteristic events that repeatedly rupture on the same fault patch in a similar way and generate nearly identical seismic waves. REs are commonly observed in high-strain rate regions (i.e., plate boundaries) but scarce in intraplate regions where strain-rate is low. In this study, we analyzed the high-precision relocations, focal mechanisms and slip rates of REs observed in aftershocks of the 2016 M_L 5.8 Gyeongju earthquake sequences in South Korea, located ~800 km away from the nearest plate boundary. We identified 70 clusters from 1405 aftershocks detected by matched filter analysis. Most of the clusters consist of two or three REs and their locations are scattered in aftershock area. On the other hand, two clusters having more than 10 REs are located near the lower limit of the seismogenic depth (~ 16 km), which is estimated from the focal depths of the aftershocks. Two clusters are on two parallel faults associated with the mainshock and the largest foreshock (M_L 5.1). REs for both clusters show strike slip mechanism but strikes for each cluster are slightly different. In addition, estimated stress drops and slip rates for REs in each cluster are also different. Given that all REs occurred during aftershock period (~ 100 days), we suggest that the coseismic and post-seismic stress perturbation may change frictional properties on the fault and makes occurrence of REs temporarily possible in specific regions.

Presenting Author: Jeong-Ung Woo

Authors