Frequency-dependent attenuation of P and S waves in Yunnan region

Abstract

We analyzed digital seismogram data of 5 668 earthquakes that occurred in Yunnan region between July of 1999 and December of 2003. Among the 22 seismic stations, six ones, namely Baoshan, Yongsheng, Lijiang, Heqing, Yimen, and Luquan, were selected and their attenuations of P and S waves were measured by using the extended coda-normalization method. The six stations were classified into three regions according to their location, that is, Baoshan area, Yongsheng-Lijiang-Heqing (YLH) area and Luquan-Yimen (LY) area. The values of Q S −1 and Q P −1 are expressed as Q S −1 =0.008 67 f −0.86, Q P −1 =0.011 55 f −0.93, Q S −1 =0.018 24 f −0.94, Q P −1 =0.022 88 f −0.92, and Q S −1 =0.016 47 f −0.91, Q P −1 =0.028 26 f −0.97 in Baoshan, YLH, LY areas respectively. The attenuation of YLH, LY are closer to each other, however, Baoshan area is apparently lower. Comparing attenuation in the three areas with other areas of the world using the same method, it is suggested that the attenuations of P and S waves in YLH and LY areas are close to Kanto of Japan, but much higher than southeast of South Korea. The Q S −1 and Q P −1 in Baoshan area are slightly higher than southeastern South Korea. Furthermore, the results indicate that our Q S −1 in Yunnan area is close to others by analyzing the coda attenuation.