Central California foreshocks of the great 1857 earthquake
Central California foreshocks of the great 1857 earthquake
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1857 年加州中部大地震的前震
DOI：
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发表时间：
1978
期刊：
影响因子：
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通讯作者：
K. Sieh
中科院分区：
文献类型：
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作者：
K. Sieh
对当代记录的分析表明，加州中部的几次小到中等地震发生在1857年大地震之前1到9小时。最早的地震显然只在旧金山弗朗西斯科地区或萨克拉门托和谢尔兰山麓地区有感觉。之后，以旧金山弗朗西斯科、维萨利亚、特洪堡和圣巴巴拉为界的地区又经历了两次范围更广的前震。通过与已知震源和震级的现代地震的有感面积和强度分布进行比较，发现后两次地震的震级为5-M_6，可能起源于半径为1060 km的区域内的某个点，其中包括圣安德烈亚斯断层历史上蠕动段的东南100 km。1857年破裂的西北端可能位于沿着。
如果这些前震的位置指示了主震的震中，那么几百公里长的主震破裂主要以单向方式向东南方向传播。这意味着，像许多大地震一样，1857年的破裂起源于历史上以中等活动为特征的断层段，并传播到历史上平静的断层段。
前震活动极有可能代表一个类似于1901年、1922年、1934年和1966年的中等帕克菲尔德-乔莱姆序列。在某种程度上，这种前兆活动是1857年断层段破坏的特征，对断层蠕动段的研究可能与预测加州中部和南部的大地震有关。
Analysis of contemporary accounts indicates that several small to moderate central California earthquakes preceded the great 1857 earthquake by 1 to 9 hr. The earliest events apparently were felt only in the San Francisco area or the Sacramento and Sierran Foothills region. Two later and much more widely felt foreshocks were experienced within the region bounded by San Francisco, Visalia, Fort Tejon, and Santa Barbara. A comparison with felt areas and intensity distributions of modern events of known source and magnitude indicates that these later two shocks were 5 ≦M ≲ 6 and probably originated at some point within an area of radius ≈60 km that includes the southeastern 100 km of the historically creeping segment of the San Andreas fault. The northwestern terminus of the 1857 rupture is probably located along this segment.
If the location of these foreshocks is indicative of the epicenter of the main event, then the several-hundred-kilometer main-event rupture propagated principally in a unilateral fashion toward the southeast. This implies that, like many great earthquakes, the 1857 rupture originated on a fault segment historically characterized by moderate activity and propagated into an historically quiet segment.
There is a strong possibility that the foreshock activity represents a moderate Parkfield-Cholame sequence similar to those of 1901, 1922, 1934, and 1966. To the extent that such premonitory activity is characteristic of the failure of the 1857 segment of the fault, studies of the creeping segment of the fault may be relevant to the prediction of large earthquakes in central and southern California.