High‐resolution image of Calaveras Fault seismicity
High‐resolution image of Calaveras Fault seismicity
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DOI：
10.1029/2001jb000633
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发表时间：
2002-09
影响因子：
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通讯作者：
D. Schaff;D. Schaff;G. Bokelmann;G. Beroza;F. Waldhauser;F. Waldhauser;W. Ellsworth
中科院分区：
文献类型：
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作者：
D. Schaff;D. Schaff;G. Bokelmann;G. Beroza;F. Waldhauser;F. Waldhauser;W. Ellsworth
通过使用波形互相关测量相对地震到达时间，并使用双差技术定位地震，我们能够将沿卡拉维拉斯断层35公里段近8000次地震的震源误差减少1到2个数量级。这代表了自1984年以来所有地震活动的92%，其中包括1984年加利福尼亚州摩根山6.2级地震的破裂带。重新定位的地震活动形成了高度组织化的结构，而这些结构以前被定位错误所掩盖。这里有丰富的重复地震序列和线性地震群。在30年的时间间隔内，地震活动中出现了几公里大小的大空洞，这表明断层的这些部分要么是被锁住的，要么是蠕动的。摩根山主震最大的滑动区域与这些空洞最突出的区域重合，这表明这部分断层可能被锁定在大地震之间。我们发现Calaveras断层在深部非常薄，断裂带宽度的平均上限为75 m。然而，在给定位置错误的情况下，此宽度无法与零确定地不同。重新定位显示了活跃的次级断层，我们用它来求解卡拉维拉斯断层附近的应力场。我们发现最大压应力与断层正线的夹角较大，仅为13°，支持了之前关于该断层较弱的解释。
[1] By measuring relative earthquake arrival times using waveform cross correlation and locating earthquakes using the double difference technique, we are able to reduce hypocentral errors by 1 to 2 orders of magnitude over routine locations for nearly 8000 events along a 35-km section of the Calaveras Fault. This represents ∼92% of all seismicity since 1984 and includes the rupture zone of the M 6.2 1984 Morgan Hill, California, earthquake. The relocated seismicity forms highly organized structures that were previously obscured by location errors. There are abundant repeating earthquake sequences as well as linear clusters of earthquakes. Large voids in seismicity appear with dimensions of kilometers that have been aseismic over the 30-year time interval, suggesting that these portions of the fault are either locked or creeping. The area of greatest slip in the Morgan Hill main shock coincides with the most prominent of these voids, suggesting that this part of the fault may be locked between large earthquakes. We find that the Calaveras Fault at depth is extremely thin, with an average upper bound on fault zone width of 75 m. Given the location error, however, this width is not resolvably different from zero. The relocations reveal active secondary faults, which we use to solve for the stress field in the immediate vicinity of the Calaveras Fault. We find that the maximum compressive stress is at a high angle, only 13° from the fault normal, supporting previous interpretations that this fault is weak.