Collaborative Research: Slip-per-event Rupture History of the San Andreas Fault in the Carrizo Plain: Was the 1857 Earthquake Characteristic?

1857年1月9日，7.8级的特洪堡地震破坏了圣安德烈斯断层南部400公里长的部分，包括卡里佐部分。圣安德烈亚斯断层的卡里佐段被认为只在最大的地震中破裂，从而控制了圣安德烈斯断层南部的大地震的发生，卡里佐平原的复发时间长达几个世纪。最近的研究结果表明，一个更复杂的破裂模式与显着更短的复发时间和可能的集群地震。报告的最近5或6次地震的每事件滑动测量结果，与新的地震日期相结合时，产生的滑动速率高达50毫米/年，远高于广泛接受的值约35毫米/年。这种不匹配表明，要么释放的应变与破裂之间的时间不成正比，从而对时间可预测和滑动可预测的弹性应变模型产生怀疑，要么报告的一些滑动每次事件测量值代表多个事件的累积滑动。这个难题的解决将导致对断层力学的基本见解，以及预测未来大地震的更有效方法。该项目的目标是测量卡里佐平原圣安德烈亚斯断层最近几次明确的断裂的滑动。挑战在于将滑动测量与地震日期联系起来。将采用几种方法，包括Bidart扇遗址的三维古地震挖掘、高精度放射性碳测年、利用高分辨率机载激光条带测绘数据分析地貌偏移，以及汇编未发表研究的档案实地数据。这项研究的结果可能对减轻地震灾害和大地震的规划产生重大影响。圣安德烈亚斯断层是人口稠密、经济重要的加州州地震灾害和风险的主要来源，其已证实的发生大地震的潜力使其成为对国家的重大威胁。这项研究的数据将有助于评估概率，并预测下一次破坏性的圣安德烈亚斯地震在南加州的位置和震级。

On January 9, 1857 the magnitude 7.8 Fort Tejon earthquake ruptured a 400 km long section of the southern San Andreas Fault including the Carrizo section. The Carrizo section of the San Andreas Fault has been proposed to rupture only during the largest earthquakes, and thereby to control the occurrence of great characteristic earthquakes on the southern San Andreas Fault with centuries-long recurrence times in the Carrizo Plain. Recent findings suggest a more complex rupture pattern with significantly shorter recurrence times and possibly clustered earthquakes. Reported measurements of slip-per-event for the last 5 or 6 earthquakes, when combined with new dates of earthquakes, yield slip rates up to 50 mm/yr, well above widely accepted values of approximately 35 mm/yr. The mismatch suggests that either the strain released is not directly proportional to the time between ruptures, thereby casting doubt on time-predictable and slip-predictable elastic strain models, or some of the reported slip-per-event measurements represent cumulative slip for multiple events. Resolution of this conundrum should lead to fundamental insights into fault mechanics, as well as more effective methods for forecasting future large earthquakes. The goal of this project is to measure the slip from several recent well-dated ruptures of the San Andreas Fault in the Carrizo Plain. The challenge is in linking slip measurements with dates of earthquakes. Several methods will be applied, including three-dimensional paleoseismic excavation of the Bidart fan site, high precision radiocarbon dating, analysis of geomorphic offsets using high resolution airborne laser swath mapping data, and compilation of archival field data from unpublished studies. Results of this research could have significant impact on seismic hazard mitigation and planning for major earthquakes. The San Andreas Fault is the major source of seismic hazard and risk in the densely populated and economically important state of California, and its proven potential to generate a large earthquake makes it a significant threat to the nation. Data from this research will help to assess the probability, and forecast the location and magnitude of the next damaging San Andreas earthquake in southern California.