2008年5月12日汶川M_W7.9地震的同震粘滑过程研究

Co-seismic Stick-slip Process during the Wenchuan, Sichuan M_W7.9 Earthquake of May, 12 2008

2008年5月12日中国汶川发生了MW7.9地震,全球数字地震仪台网(GSN)74个台的地震仪和陕西周至地震台的数字水位仪都很好地记录到了该地震的同震粘滑错动过程和止滑过程。分析GSN74个地震台的记录后发现:汶川MW7.9地震的同震粘滑错动过程是一次多点粘滑错动过程,主要由四个子粘滑错动事件构成,整个粘滑错动过程的持续时间不少于86.6s;地震的弹性破裂过程与粘滑错动过程同时进行,是粘滑错动和弹性破裂共同作用的结果,是一种“粘滑错动+弹性破裂”的机制。对周至地震台数字水位仪记录分析后发现:汶川地震的同震粘滑错动过程与P.N.Sundaram[1]作的岩石粘滑错动实验结果一致,粘滑错动过程可细分为粘结(stick)和滑动(slip)二个过程。汶川地震在止滑过程中激发出了长周期勒夫面波(XsQ)和瑞雷面波(XsR)。研究粘滑震相有助于认识震源的粘滑错动过程,研究止滑震相有助于预判震灾损失。

The results of rock stick-slip dislocation experiments in the laboratory show that one stick-slip dislocation process includes three stages generally: pre-slip stage, stick-slip stage, and stop-slip stage. We found the stick-slip dislocation process is often not a single point stick-slip dislocation process, but is composed of multi-point stick-slip dislocation process, showing the characteristic of multi-point stick-slip dislocation in the different parts of the fault. A strong earthquake of magnitude M W7.9 occurred at Wenchuan, China, on May 12, 2008. The process of coseismic stick-slip dislocation and stop-slip process of the earthquake were recorded perfectly by the digital seismograph of Global Seismographic Network’s (GSN) 74 seismic stations and the deep borehole water level digital instrument of Zhouzhi seismic station, China. After analyzing these recordings, we find that multi point stick-slip dislocation process during the Wenchuan M W7.9 earthquake. According to the observational evidence, the stick-slip dislocation process may be composed by four sub-stick-slip dislocation events.The duration time of whole process of stick-slip dislocation is more than 86.6 s. We infer to the Wenchuan M W7.9 earthquake may be a result of elastic rupture and stick-slip dislocation commonly. It is a kind of "stick-slip dislocation + elastic rupture" mechanism. After analyzing the recording of deep borehole water level digital instrument of Zhouzhi seismic station, we find the results of coseismic stick-slip dislocation process of Wenchuan M W7.9 earthquake are consistent with the rock stick-slip dislocation experimental results of P. N. Sundaram [1]. The stick-slip dislocation process can be divided into the stick and the slip two process. The stop-slip phase XsQ and XsR are excited during the stop-slip process of Wenchuan M W7.9 earthquake. The XsQ and XsR phase are Love type surface wave and Rayleigh type surface wave, respectively. The travel time relationships of P+Xs1, Xs2, Xs3, Xs4, XsQ and XsR phases are given, at Δ= 5.3°-121.0°. Studying the Xs phase will be helpful for understanding the processes of the stick-slip dislocation. Studying the XsQ and XsR phase will be helpful for judging disaster loss of the great earthquake.