Collaborative Research: Multi-cycle Rupture History of the San Andreas Fault in the Carrizo Plain

地震物理学、地震灾害和新构造学中最基本的问题之一是“是什么控制着地震活动的时空模式？一个必须首先回答的更基本的问题是：“地震活动的时空模式是什么？”“这个问题只能通过在多个时间和空间尺度上观察故障行为来回答。古地震调查提供了一部分断层的多周期破裂历史的数据。圣安德烈亚斯断层是加州最大的地震危险源。关于圣安德烈亚斯断层破裂历史的数据构成了许多断层行为和地震危险性模型的基础。圣安德烈亚斯断层的高滑动率，短复发间隔，大长度和可达性使其成为美国（也许是世界）断层行为模型观测测试的最佳目标。该项目涉及从世界上最具科学意义和最危险的断层之一--圣安德烈亚斯断层--的一个已证实的古地震遗址沿着收集多周期破裂历史。沿着南圣安德烈亚斯断层沿着只有4个地点的断裂年代学至少有5个事件。其中一个地点是卡里佐平原的比达特风扇。卡里佐平原是研究SAF断裂历史的最佳地点之一，因为它具有经过验证的古地震记录，具有出色的滑动率和每次事件滑动测量，并且有可能通过增加地震记录的长度来显着扩大数据集。 以前在比达特扇的工作表明，它包含了一个漫长的，可确定日期的表面破裂记录。在Bidart Fan的苏丹武装部队控制区共挖掘了四条战壕。这些海沟产生了一个复合年表，包括过去3,000年来Bidart Fan的10次表面破裂。最近的5次地震的日期相当准确，但更早的5次破裂的日期的不确定性要大得多。因此，这五次早期地震是本项目的首要目标。在比达尔特扇上放置的额外沟槽揭示了整个扇上沉积的更好的空间和时间记录，从而改进了先前记录的地震日期。样品的放射性碳年代测定将从加州大学欧文分校新的凯克加速器质谱仪设施获得，该设施专门用于碳同位素，利用劳伦斯利弗莫尔国家实验室在古地震学中应用放射性碳年代测定的改进。该项目包括一项类似的努力，以改善卡里佐平原的事件记录。它使卡里佐平原地表破裂的时间记录翻了一番，并为开发和测试断层行为模型提供了圣安德烈亚斯断层上的主要古地震现场。

One of the most basic questions in earthquake physics, earthquake hazards, and neotectonics is "What controls the space-time pattern of seismicity?" A more fundamental question that must be answered first is "What is the space-time pattern of seismicity?" This question can only be answered by observing fault behavior at multiple temporal and spatial scales. Paleoseismic investigations provide data on the multi-cycle rupture history of a portion of a fault. The San Andreas fault is the largest source of seismic hazard in California. Data on the rupture history of the San Andreas fault form the basis of numerous models of fault behavior and seismic hazard. The high slip rate, short recurrence interval, great length and accessibility of the San Andreas fault make it the best target in the U.S. (and perhaps the world) for observational testing of fault behavior models. This project involves collecting a multi-cycle rupture history from a proven paleoseismic site along one of the most scientifically important and hazardous faults in the world: the San Andreas fault. There are only 4 sites along the southern San Andreas fault that have a rupture chronology of at least 5 events. One of these sites is the Bidart Fan in the Carrizo Plain. The Carrizo Plain is one of the best places to study the rupture history of the SAF because it has a proven paleoseismic record with excellent slip rate and slip per event measurements, and the potential to significantly enlarge the data set by increasing the length of the earthquake record. Previous work at the Bidart Fan shows that it contains a lengthy, datable record of surface ruptures. A total of four trenches have been excavated in the SAF zone on the Bidart Fan. These trenches yield a composite chronology consisting of 10 surface ruptures of the Bidart Fan over the last 3,000 years. The most recent 5 earthquakes are reasonably well dated, but uncertainty in the dates of the five earlier ruptures is much greater. Therefore, these five early earthquakes are the primary target of this project. Additional trenches placed across the Bidart Fan are revealing a better spatial and temporal record of deposition across the fan, leading to improved dates of previously documented earthquakes. Radiocarbon dates of samples will be obtained from University of California, Irvine's new Keck Accelerator Mass Spectrometry facility devoted to carbon isotopes using improvements in the application of radiocarbon dating to paleoseismology made at the Lawrence Livermore National Laboratory. This project includes a similar effort to improve the event record in the Carrizo Plain. It is doubling the temporal record of surface ruptures in the Carrizo Plain and providing a major paleoseismic site on the San Andreas fault for developing and testing models of fault behavior.