【摘要】 使用区域固定台网数字地震记录资料,计算2013年4月20日四川芦山MS7.0地震余震序列的震源谱参数,通过纵、横波的拐角频率比值和纵、横波位移谱零频极限比值计算波速比。结果显示:1拐角频率比值得到的波速比平均值约为1.27,零频极限比值得到的波速比平均值约为1.67,零频极限比值得到的结果更接近泊松介质的波速比1.73;2两种方法得到的波速比变化趋势基本一致:在主震后均处于较低异常水平,最后一个MS5.4余震后,波速比回返升高;3零频极限比值得到的波速比异常形态较明显,在3个MS5.4余震前都呈现出"降低-回返"的过程,在回返之后发生最大余震;4在数据处理过程中,是否对介质做非弹性衰减校正对两种方法的结果影响不大;5单台波速比与多台波速比的变化趋势基本一致。更多还原

【Abstract】 Based on seismic waveform data recorded by National Digital Seismic Network from April 20,2013 to December 2013,we calculated the source spectrum parameters of earthquakes with ML≥3.0of the Lushan earthquake sequence,using the ratio of P-wave to S-wave corner frequency and the ratio of P-wave to S-wave long-period spectral level to calculate the velocity ratio.The results indicate that:1 The average VP/VSobtained from the ratio of corner frequency is 1.27 while the average VP/VSobtained from the ratio of long-period spectral level is 1.67,which is closer to the value 1.73 of Poisson medium.2 Velocity ratios obtained from the two methods have a common variation tendency:after the mainshock the velocity ratio was at a low value anomalies until the last MS5.4aftershock,since then the velocity ratio recovered to the level above the average.3 The velocity ratio anomaly calculated from the long-period spectral level behaved more evidently,it presents a ‘decline-recovery-occurrence’process before the three MS5.4aftershocks.4 Correction for medium attenuation has no big effect on the results getting from the two methods.5 The velocity ratios obtained from single seismic station and multi-station have the same variation tendency.更多还原