A 300- to 550-year history of slip on the Imperial fault near the U.S.-Mexico border: Missing slip at the Imperial fault bottleneck
A 300- to 550-year history of slip on the Imperial fault near the U.S.-Mexico border: Missing slip at the Imperial fault bottleneck
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美墨边境附近帝国断层上 300 至 550 年的滑动历史：帝国断层瓶颈处缺失的滑动
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发表时间：
1996
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影响因子：
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通讯作者：
T. Rockwell
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作者：
A. P. Thomas;T. Rockwell
对墨西卡利谷美墨国际边界以南约 50-60 m 的帝国断层带进行的地下调查显示，在过去 300 年中，只有 1940 年的帝国谷地震 (M L 7.1) 才产生了明显的地表滑移。 1940 年的地震在该附近产生了约 5 m 的滑移，如偏移树线所示。我们在这些树木附近挖掘了一条埋藏通道，并确定它也偏移了 5 m。这些数据表明，至少上层沉积物仅在 1940 年的事件中发生了位移。大约 300 年前，在最后一个湖泊的湖相高位沉积物中记录了另一次规模未定的滑动事件。没有证据表明沉积物中的早期断层事件可能与距今大约 550 年的倒数第二个湖泊有关。在不整合面下方，大约有 4000 年历史的三角洲沉积物因先前沿着帝国断层的滑动而发生强烈断层。这些数据表明，过去 300-550 年帝国断层的滑动率仅为约 15-20 毫米/年，远低于大地测量和区域构造模型的预期。这反过来表明，要么滑动被边界区域的其他断层所容纳，要么帝国断层上的应变释放具有情景（集群）行为的特征。
Subsurface investigation of the Imperial fault zone approximately 50-60 m south of the U.S.-Mexico International Border in Mexicali Valley reveals that only the 1940 Imperial Valley earthquake (M L 7.1) has produced significant surface slip in the past 300 years. The 1940 earthquake produced about 5 m of slip in this vicinity, as indicated by an offset tree line. We excavated a buried channel adjacent to these trees and determined that it is also offset 5 m. These data indicate that at least the upper meter of sediments has only been displaced by the 1940 event. One other slip event of undetermined magnitude is recorded within the lacustrine highstand deposits of the last lake about 300 years ago. There is no evidence of earlier faulting events in sediments that possibly may correlate to the penultimate lake approximately 550 years B.P. Below an unconformity, ∼4000-year-old deltaic deposits are intensely faulted by previous slip along the Imperial fault. These data suggest that the slip rate on the Imperial fault for the past 300-550 years is only about 15-20 mm/yr, substantially less than that expected from geodetic measurements and regional structural models. This in turn suggests that either slip is accommodated by other faults in the border region or that strain release on the Imperial fault is characterized by episodic (clustered) behavior.