Analysis of M 3.5 Geochang earthquake on February 5, 2013 and its aftershocks

Abstract:

The Korean Peninsula is located in an intraplate region, where the current seismicity is low. Recently, there were unusual several serial offshore earthquakes occurred around the southern Korean Peninsula. In addition, on 5 February 2013, a small-sized earthquake (ML 3.5) occurred in the central south of the southern Korean Peninsula and it had unusual number of aftershocks. The multi-channel cross-correlation method was applied to the 4 weeks of continuous seismograms from the nearest seismic station that includes the 2 weeks before and 2 weeks after the main event, which revealed that this event was accompanied by more than 54 micro aftershocks. The 12 events, including the main event, with magnitude greater than 1.0 were selected for further analysis to investigate the characteristics of the main event: focal mechanism and its source parameters. The focal mechanism of the events was determined from the first P motion polarities. The Joint Hypocenter Determination method for the 12 events indicated that a left-lateral vertical strike-slip fault would be the possible fault plane. The source parameters of the main event were obtained by the empirical Green’s function method. The fault radius and the stress drop were estimated to 0.3~0.5±0.1 km and 30~50±20 bar, respectively, while the stress drop was about 49 bar from S wave displacement spectra by which the moment magnitude and the corner frequency were estimated to 3.83 and 3.21 Hz, respectively.