用于龙门山断裂南段深部介质探测的精密可控震源

The controlled accurate seismic source for exploration of deep medium below south part of the Longmenshan fault zone

摘要:

汶川地震后在龙门山断裂带南段建立了精密可控震源发射台，结合布设的28套流动地震仪的信号记录，尝试监测地下介质的动态应力变化。为了提取记录中的主动源发射的信号，本文采用了匹配滤波方法来实现弱信噪比条件下的信号检测并进行了波形变换。在提取出每个周期的主动源信号后，利用信号叠加，分别获得了1、5、10天时间的波形，有效地提高了记录波形的信噪比。然后通过互相关检测精确得出地震波的走时变化，并分析了计算误差。最后，针对实验期间发生的绵竹MS5.6地震进行分析，获得了地震前后的走时剖面和信号变化，结果表明，距离较远的龙门山断裂北段地震未能对南段实验区域的地下介质波速产生影响。

Abstract:

In order to monitor temporal stress variation of underground medium，we built a signal transmitters based on the Controlled Accurate Seismic Source(CASS)near south part of Longmenshan Fault zone after the Wenchuan MS8.0 earthquake in 2008. 28 seismometers were set up to record the elastic waves emitted from the CASS. The source signal was detected in the records with low signal to noise ratio of the seismic stations，and transformed to seismic wavelet by matched filter technique. Then the SNR of the seismic wavelet was improved by stacking technique，and seismic wavelet of every day，every 5 days and every 10 days were obtained. In addition，the variation of seismic travel time was extracted by cross-correlation and the error range was assessed. Using CASS system is feasible for monitor variation of seismic travel time from the result. Finally，we compared and analyzed the variation of seismic travel time before and after the Mianzhu MS5.6 earthquake in 2009. The result showed that the earthquake with long distance had no effort on the seismic velocity of underground medium below our experimental region.