Study Of Attenuation Structure Based On The Dense Networks Around South Korea

There are few seismic studies of South Korea because this region has relatively quiet seismicity as a typical intraplate environment and lack of seismic stations (e.g. Lee et al., 2003). Recently, however, the densification of regional seismic network has been proceeded in S. Korea since 1999. Based on the dense network data, we first reported not only focal mechanisms of nationwide microseismicity (Chung et al., 2004) but also body wave attenuation structure for several regions (Chung and Sato, 2001; Kim et al., 2004) in S. Korea. These attenuation studies using the coda normalization method (CNM) showed very low Q_P^-1 and Q_S^-1 values comparable to those of seismically stable regions. By using the CNM, we also studied Q_Lg^-1 value (Chung and Lee, 2003), which is similarly low value with Q_S^-1. To compensate the lack of data, the source pair/receiver pair method (SPRP) was applied to 71 earthquakes for further Q_Lg^-1 attenuation study (Chung et al., 2004). The SPRP provided nearly 1500 source-receiver pairs and reproduced Q_Lg^-1 for all frequencies less than 0.002, which is a reasonable value for a seismically inactive region. Lately, we have continued to analyze Lg attenuation structure by adding dense Japanese network located in Kyushu, near southeast of S. Korea. In this analysis, we used the reversed two-station method for collinearly aligned event and receiver pairs to correct azimuthal effect of Lg in the previous SPRP study. Refernces Chung, T.W. and, H. Sato, 2001, BSSA, v.91, 1867-1874. Chung, T.W. and, K. Lee, 2003, BSSA, v.93, 1401-1406. Lee, K., N.S. Chung, and, T.W. Chung, 2003, BSSA, v.93, 2131-2145. Kim, K.D., T.W.Chung, J.B. Kyung, 2004, BSSA, v.94, 1070-1078. Chung, T.W., J.C. Park, and W. Kim, 2004, PEPI, in submitted. Chung, T.W., Y.K. Park, I.B.Kang, and K. Lee, 2004, BSSA, in submitted.