San Andreas Fault Geometry at Desert Hot Springs, California, and Its Effects on Earthquake Hazards and Groundwater
San Andreas Fault Geometry at Desert Hot Springs, California, and Its Effects on Earthquake Hazards and Groundwater
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DOI：
10.1785/0120080117
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发表时间：
2009-08-01
影响因子：
3
通讯作者：
Gandhok, G.
中科院分区：
文献类型：
--
作者：
Catchings, R. D.;Rymer, M. J.;Gandhok, G.
使命溪和班宁断层是位于加州南部科切拉谷北方的圣安德烈亚斯断层带的两条主要断层。断裂构造特征对区域地震灾害和地下水资源都有重要影响。我们使用地震，重力和地质数据来描述圣安德烈亚斯断层带附近的沙漠温泉。沙漠温泉的使命溪断层上部500 m的地震图像显示，多个断层链分布在500 m宽的区域内，断层集中在断层带中央200 m宽的区域内。断层东北侧的高速（高达5000米/秒）岩石与西南侧的低速（< 2000米/秒）盆地并列，在上方几百米内。使命溪断层的近地表部分向西南和东北方向急剧倾斜，并在深度处合并，形成一个狭窄的、急剧西南倾斜或接近垂直（80度至90度）的断层带。相反，班宁断层向东北倾斜（45度至70度），朝向使命溪断层，这两个断层可能在深处合并成一个单一的圣安德烈亚斯断层带，表明一个张扭断层系统。该地区历史上最大的两次（M > 6：0）地震（1948年和1986年）的主震震源发生在合并（圣安德烈亚斯）断层的深度（类似于10至12公里）或附近。在合并断层处或其下成核的大规模地震将可能从沿两个断层带沿着的导波以及从两个断层带之间的低速盆地中的放大地震波产生强烈的震动。使命溪断层带是一个地下水屏障，地下水位顶部深度变化60 m，含水层厚度变化约50 m，横跨200 m宽的集中断层带。
The Mission Creek and Banning faults are two of the principal strands of the San Andreas fault zone in the northern Coachella Valley of southern California. Structural characteristics of the faults affect both regional earthquake hazards and local groundwater resources. We use seismic, gravity, and geological data to characterize the San Andreas fault zone in the vicinity of Desert Hot Springs. Seismic images of the upper 500 m of the Mission Creek fault at Desert Hot Springs show multiple fault strands distributed over a 500 m wide zone, with concentrated faulting within a central 200 m wide area of the fault zone. High-velocity (up to 5000 m/sec) rocks on the northeast side of the fault are juxtaposed against a low-velocity (< 2000 m/sec) basin on the southwest side within the upper few hundred meters. Near-surface strands of the Mission Creek fault dip steeply southwestward and northeastward and merge at depth to form a narrower, steeply southwestward-dipping or near-vertical (80 degrees to 90 degrees) fault zone. The Banning fault, in contrast, dips northeastward (45 degrees to 70 degrees) toward the Mission Creek fault, and the two faults likely merge into a single San Andreas fault zone at depth, indicating a transtensional fault system. Mainshock hypocenters for two of the historically largest (M > 6: 0) earthquakes in the area (in 1948 and 1986) occurred at or near the depths (similar to 10 to 12 km) of the merged (San Andreas) fault. Large-magnitude earthquakes that nucleate at or below the merged fault will likely generate strong shaking from guided waves along both fault zones and from amplified seismic waves in the low-velocity basin between the two fault zones. The Mission Creek fault zone is a groundwater barrier with the top of the water table varying by 60 m in depth and the aquifer varying by about 50 m in thickness across a 200 m wide zone of concentrated faulting.