利用纵、横波震源谱参数研究波速比——以岷县—漳县MS6.6地震为例

利用甘肃省区域地震台网提供的地震波形,计算得到甘肃东南地区2010年1月至2014年6月183个M_L≥2.5地震纵、横波的拐角频率和零频极限等震源谱参数,分析2013年7月22日岷县—漳县M_S6.6地震前后纵、横波拐角频率比值和零频极限比值的变化特征,间接反映震源处波速比的变化。结果如下:(1)拐角频率比值的平均值约为1.32,而由零频极限比值计算得到的波速比平均值约为1.55,后者高于前者;(2)二者得到波速比的时间变化趋势基本一致:两个波速比在岷县地震前后呈现出"明显升高-下降-震前急剧下降-震后缓慢恢复"的变化过程;(3)二者得到的波速比空间分布基本一致:岷县地震震中附近及合作、舟曲等地区在震前出现低值异常,震中附近地区的波速比在震后有所回升。

Wave velocity ratio of the Minxian-Zhangxian MS6.6 earthquake from source spectral parameters of P-wave and S-wave

In this paper,the source spectral parameters of 183 M_L≥2.5 earthquakes from January 2010 to June 2014 in southeastern Gansu were calculated by using the seismic waveform in the regional seismic network of Gansu Province.The variation characteristics of the ratio of P-wave corner frequency to S-wave and the ratio of P-wave long-period spectral level to S-wave before and after the Minxian M_S6.6 earthquake on July 22,2013 were analyzed,as well as the change of wave velocity ratio.The results indicate that:(1)The average value of corner frequency ratio is about 1.32,and the average value of wave velocity ratio calculated from the long-period spectral level ratio is about 1.55,higher than the former.(2)The time variation trends of the wave velocity ratios obtained by the two source spectral parameters are basically the same:“obvious rise-decline-sharp decline before the earthquake-slow recovery after the earthquake”;(3)The spatial distribution of wave velocity ratios are basically the same:low value anomalies appeared near the epicenter of Minxian earthquake before the earthquake,and the wave velocity ratio near the epicenter rebounded after the main shock.