Double-difference Relocation of Earthquakes in Western Korea, 2009-2015

Abstract:

There have been low to moderate seismicity in the Korean peninsula over the last two thousand ears. Interpreting earthquakes with small- to medium-size has difficulty because epicenters of these earthquakes are not clearly associated with major faults or boundaries of major geological units. We relocate events (M_L 0.4 ~ 3.9) that occurred in the western part of South Korea (35.5 ~ 38.5 °N 124.5 ~ 128 °E) from January 2009 to January 2015. We first make 21 groups from 495 events with local magnitude greater than 2 using kernel density estimation in the studied area. Second, we cross-correlate and classify events for each group, and define a set comprised of events with cross-correlation coefficient (CC) greater than 0.7. Events with local magnitude smaller than 2 are also assigned to a relevant set according to the value of CC (> 0.7). Finally, we relocate epicenters of events from the same set using travel-time double-differences computed by cross-correlation for Lg-wave. Relocated epicenters are more clustered by a factor of several tens, and their spatial distribution reflect location of classified events. For some earthquake sequences with good station coverage, the relocated epicenters lead us to reveal spatiotemporal migration of events, and is able to image structure of seismicity associated with a fault in fine-scale.