Continuing Studies of the Strengthening of the Fault Zone Ruptured in the 1992 Landers, California Earthquake by Monitoring Fault Zone Waves

9804811利用断裂带导波对1992年7.5级地震后兰德斯断裂带的三维结构和加固过程进行了连续监测。早期对兰德斯余震的断裂带捕获波的研究使约翰逊谷断层(兰德斯南部破裂面)的圈定深度至少达到10公里，其标志是一个约200米宽的低速波导，其中剪切速度降低了30%-50%，Q约为30。1994年和1996年在约翰逊河谷沿线使用爆炸震源进行的重复地震调查显示，地震速度随时间增加。这些观察表明，断裂带随着时间的推移而加强，这可能是由于裂缝的闭合。这笔赠款将支持在1998年和2000年重复这一实验。其目的是进一步了解地震破裂过程，并开发预测未来地震中已知断层分段的方法。这项研究是国家地震减灾计划的一部分。*

9804811Li This research involves the continuation of the monitoring, by means of fault zone guided waves, the Landers fault zone 3-D structure and strengthening process after the M = 7.5 earthquake of 1992. Earlier studies of fault zone trapped waves from Landers aftershocks allowed the delineation of the Johnson Valley fault (the Landers southern rupture plane) to a depth of at least 10km, marked by a low velocity waveguide approximately 200 m wide where shear velocity is reduced by 30 to 50 percent and Q is about 30. Repeat seismic surveys in 1994 and 1996 using explosive sources along the Johnson Valley revealed an increase in seismic velocities with time. These observations indicate a strengthening of the fault zone with time that may be due to a closure of cracks. This grant will support a repeat of this experiment in 1998 and 2000. The goal is to further understand the earthquake rupture process and develop methods for predicting the segmentation of known faults in future earthquakes. This research is a component of the National Earthquake Hazard Reduction Program.***