Paleoseismology and Geomorphology of the Raymond Fault, Los Angeles County, California
Paleoseismology and Geomorphology of the Raymond Fault, Los Angeles County, California
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加利福尼亚州洛杉矶县雷蒙德断层的古地震学和地貌学
DOI：
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发表时间：
2000
期刊：
影响因子：
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通讯作者：
J. Dolan
中科院分区：
文献类型：
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作者：
Kristin D. Weaver;J. Dolan
雷蒙德断层以宽阔的南凸弧形延伸 20 公里，横跨洛杉矶东北部人口稠密的圣盖博谷。尽管朝南的陡坡是断层的大部分特征，但地貌和地震学证据表明左旋运动占主导地位。断层东端结晶基底脊明显左旋 3.4 公里，可能近似于断层上的总滑移。来自我们的一个古地震沟的数据，结合已发表的数据，表明最近的雷蒙德断层表面破裂发生在~1-2ka。对断层面面积的估计表明，整个雷蒙断层的破裂可能会产生 M w ∼ 6.7 级地震。雷蒙德断层和好莱坞断层沿着向西走向的相似运动学，加上明显的断层平行重力线和稀疏的地貌证据，表明这两个断层之间可能存在贯穿的机械联系，并且可以想象它们可能在大地震中一起破裂。然而，已发表的数据表明，好莱坞断层最近~6-9ka破裂到地表，这表明最近的雷蒙德断层表面破裂显然没有向西延伸到好莱坞断层。来自我们另一个古地震沟的数据提供了至少五次最新更新世地震的证据，其中包括至少四次地表破裂，这些破裂发生在~31.5 ka和41.5 ka之间的短暂、≤10,000年的时期内。这些事件的平均复发间隔≤3300年，比根据先前海沟中发现的古地震频率所建议的过去约40,000年的间隔要短得多。因此，要么 31.5 ka 至 41.5 ka 事件代表一个时间簇，并且断层的复发间隔高度不规则，要么自 31.5 ka 以来发生的所有雷蒙断层地震中至少有一半尚未被识别。
The Raymond fault extends for 20 km in a broad convex-to-the-south arc across the densely populated San Gabriel Valley northeast of Los Angeles. Although south-facing scarps characterize much of the fault, geomorphic and seismological evidence indicate a predominance of left-lateral motion. An apparent 3.4-km left-lateral offset of a crystalline basement ridge at the east end of the fault may approximate total slip on the fault. Data from one of our paleoseismologic trenches, in combination with published data, indicate that the most recent Raymond fault surface rupture occurred ∼1–2 ka. Estimates of fault-plane area suggest that rupture of the entire Raymond fault could generate an earthquake of M w ∼ 6.7. The similar kinematics of the Raymond fault and the Hollywood fault, along strike to the west, together with a pronounced fault-parallel gravity lineament and sparse geomorphic evidence, suggests that there may be a through-going mechanical connection between the two faults, and that they could conceivably rupture together in large earthquakes. Published data, however, indicate that the Hollywood fault ruptured to the surface most recently ∼6–9 ka, indicating that the most recent Raymond fault surface rupture apparently did not extend westward onto the Hollywood fault. Data from another of our paleoseismologic trenches yielded evidence for at least five latest Pleistocene earthquakes, including at least four surface ruptures that occurred during a brief, ≤10,000-year-long period between ∼31.5 and 41.5 ka. The ≤3300 year-long, average recurrence interval for these events is much shorter than the interval suggested for the past ∼40,000 years by the frequency of paleoearthquakes recognized in previous trenches. Thus, either the 31.5 ka to 41.5 ka events represent a temporal cluster, and the recurrence interval for the fault is highly irregular, or at least half of all Raymond fault earthquakes that have occurred since ∼31.5 ka have not yet been recognized.