Seismic moment, stress, and source dimensions for earthquakes in the California‐Nevada region
Seismic moment, stress, and source dimensions for earthquakes in the California‐Nevada region
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DOI：
10.1029/jb073i014p04681
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发表时间：
1968-07
影响因子：
--
通讯作者：
M. Wyss;J. Brune
中科院分区：
文献类型：
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作者：
M. Wyss;J. Brune
通过表面波分析、震源区表面位移观测、震级测定和准确震中位置，研究了加利福尼亚-内华达地区的地震震源机制。对 Parkfield 地区 13 次地震的表面波进行傅立叶分析，得到了地震矩 M0 和里氏震级 ML 之间的关系：log M0 = 1.4 ML + 17.0，其中 3 < ML < 6。获得了表面波包络参数 AR 和地震矩之间的以下关系：log M0 = log AR300 + 20.1。该关系用于估计美国西部另外 259 次地震的地震矩。组合数据得出矩与当地震级之间的关系如下：log M0 = 1.7 ML + 15.1，其中 3 < ML < 6。这些数据与 Gutenberg-Richter 能量震级公式一起表明，对于 Parkfield 和 Imperial Valley 的小地震，平均应力乘以地震效率约为 7 条，对于白狼断层惠勒岭附近的小地震，平均应力乘以地震效率约为 30 条，对于白狼断层惠勒岭附近的小地震，平均应力乘以地震效率约为 7 条。亚利桑那州-内华达州和拉古纳萨拉达（下加利福尼亚州）地区发生小地震。对与八次帕克菲尔德地震相关的位移的现场观测以及对断层面积的估计表明，断层尺寸与先前在帝国地震中发现的值相似是规则，而不是沿圣安德烈亚斯断层发生的小地震的例外。应力降似乎约为平均应力乘以地震效率的 10%。修正后的力矩与震级曲线进一步强调，小地震对于应变释放并不重要，并表明帝王谷的剪切带垂直范围可能约为 6 公里，而海洋转换断层的剪切带甚至更短。
The source mechanism of earthquakes in the California-Nevada region was studied using surface wave analyses, surface displacement observations in the source region, magnitude determinations, and accurate epicenter locations. Fourier analyses of surface waves from thirteen earthquakes in the Parkfield region have yielded the following relationship between seismic moment, M0 and Richter magnitude, ML: log M0 = 1.4 ML + 17.0, where 3 < ML < 6. The following relation between the surface wave envelope parameter AR and seismic moment was obtained: log M0 = log AR300 + 20.1. This relation was used to estimate the seismic moment of 259 additional earthquakes in the western United States. The combined data yield the following relationship between moment and local magnitude: log M0 = 1.7 ML + 15.1, where 3 < ML < 6. These data together with the Gutenberg-Richter energy-magnitude formula suggest that the average stress multiplied by the seismic efficiency is about 7 bars for small earthquakes at Parkfield and in the Imperial Valley, about 30 bars for small earthquakes near Wheeler Ridge on the White Wolf fault, and over 100 bars for small earthquakes in the Arizona-Nevada and Laguna Salada (Baja California) regions. Field observations of displacement associated with eight Parkfield shocks, along with estimates of fault area, indicate that fault dimensions similar to the values found earlier for the Imperial earthquake are the rule rather than the exception for small earthquakes along the San Andreas fault. Stress drops appear to be about 10% of the average stress multiplied by the seismic efficiency. The revised curve for the moment versus magnitude further emphasizes that small earthquakes are not important in strain release and indicate that the zone of shear may be about 6 km in vertical extent for the Imperial Valley and even less for oceanic transform faults.