Li YG, Vidale JE, Aki K, Xu F, Burdette T
Y.-G. Li and K. Aki, Department of Earth Sciences, University of Southern California, Los Angeles, CA 90089-0740, USA. J. E. Vidale and F. Xu, Department of Earth and Space Sciences, University of California at Los Angeles, Los Angeles, CA 900.
Science. 1998 Jan 9;279(5348):217-9. doi: 10.1126/science.279.5348.217.
Repeated seismic surveys of the Landers, California, fault zone that ruptured in the magnitude (M) 7.5 earthquake of 1992 reveal an increase in seismic velocity with time. P, S, and fault zone trapped waves were excited by near-surface explosions in two locations in 1994 and 1996, and were recorded on two linear, three-component seismic arrays deployed across the Johnson Valley fault trace. The travel times of P and S waves for identical shot-receiver pairs decreased by 0.5 to 1.5 percent from 1994 to 1996, with the larger changes at stations located within the fault zone. These observations indicate that the shallow Johnson Valley fault is strengthening after the main shock, most likely because of closure of cracks that were opened by the 1992 earthquake. The increase in velocity is consistent with the prevalence of dry over wet cracks and with a reduction in the apparent crack density near the fault zone by approximately 1.0 percent from 1994 to 1996.
对1992年发生里氏7.5级地震的加利福尼亚州兰德斯断裂带进行的多次地震勘测显示，地震波速度随时间增加。1994年和1996年，在两个地点通过近地表爆炸激发了P波、S波和断裂带捕获波，并记录在横跨约翰逊谷断层迹线部署的两个线性三分量地震台阵上。从1994年到1996年，相同炮点-接收点对的P波和S波走时减少了0.5%至1.5%，在断裂带内的台站变化更大。这些观测结果表明，主震后约翰逊谷浅层断层正在强化，最有可能的原因是1992年地震所开启的裂缝闭合。速度增加与干裂缝多于湿裂缝的情况相符，且与1994年至1996年期间断裂带附近的表观裂缝密度降低约1.0%相符。
