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1979年3月15日,在加利福尼亚州圣贝纳迪诺县莫哈维沙漠地区兰得斯西北的霍姆斯特河谷,发生一系地震,并且沿着两条平行断裂带伴生地裂缝(图1)。第一次地震为里氏震级4.0级,接着发生了5.2级(1点07分)、4.5级(1点34分)和4.8级(3点07分)地震,还记录到许多较小的余震。这几次事件中,在约翰逊河谷断层和一条未命名的断层上及其附近伴生地裂缝(图1)。据加州理工学院地震实验室的初步数据,霍姆斯特河谷的主震震中定于北纬34°18.5′、西经116°26.4′,约在两条地裂缝带的中部。地震活动开始以后几小时内开始了系统的野外调查,监测余震、地球物理场的局部变化
On March 15, 1979, a series of earthquakes occurred in the Holmster Valley, northwestern of Randas, in the Mojave Desert State of San Bernardino County, California, and along the two parallel fractures associated with ground fissures 1). The first earthquake was Richter magnitude 4.0, followed by 5.2 (1.07), 4.5 (1:34) and 4.8 (3.07) earthquakes, and many smaller aftershocks . In these incidents, ground fissures have occurred in and around the Johnson Valley fault and an unnamed fault (Figure 1). According to preliminary data from the California Institute of Technology Earthquake Laboratory, the main shock of the Holmes Valley is centered at 34 ° 18.5 ’north latitude and 116 ° 26.4 west long, about the middle of two ground fissures. Within a few hours after the start of the seismic activity, a systematic field investigation was started to monitor aftershocks and local changes in the geophysical field