云南姚安地区S波和尾波的场地放大

Site Amplifications for S Waves and Coda in the Yao’an Area,Yunnan

本文利用2000年1月15日姚安MS6.5地震的153个余震的1446条水平运动地震记录的S波和尾波谱振幅资料,用线性反演法和频谱比法估测了姚安震区的场地放大因子。姚安台位于姚安盆地第四系冲积层上,对应苤拉基岩台,在3～6Hz低频段S波有3～4倍的放大因子,尾波有6～7倍的放大因子。大河口、马游、官屯和巴拉台架设在盆地西部山区侏罗系或白垩系岩石基底上的残积坡积层上,在10Hz以下低频段,其场地放大因子与苤拉台相近。姚安台较大的放大因子表明其下有软弱层,尾波和S波的放大因子的差别表明盆地内存在陷获波而使尾波增强。

The site amplification factors were estimated using 1446 horizontal conponent seismograms for 153 aftershocks of 15 January 2000 earthquake with Ms6.5 in Yao＇ an, Yunnan. The Yao＇ an station （YAON） was installed on the Quaternary allurium in the Yao＇an basin and has a site amplification factor of 3 to 4 for S-waves and that of 6 to 7 for coda relative to the rock reference station Pila（PILA） in the frequency range of 3 to 6 Hz. The Dahekou（DAHK）, Mayou（MAYU）, Guantun（GUAT） and Balaza（BALZ） stations were deployed on the sedentary soil overlying the Jurasic or Cretaceous rocks to the west of the Yao＇ an basin and have approximate site amplification factors to that of the reference station below frequency 10Hz. The larger site amplification factor of YAON indicates that there exists soft layer in the basin, and the differences of the site amplification facters between S wave and coda show that the trapped wave in the basin strengthen the coda.