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“是什么控制了地震活动的时空模式？”首先必须回答的一个更根本的问题是“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断层行为来回答。古地震研究提供了断层部分的多旋回破裂历史数据。圣安德烈亚斯断层是加州最大的地震危险来源。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速率、短重复间隔、大长度和可访问性使其成为美国(甚至可能是世界)对断层行为模型进行观测测试的最佳目标。该项目包括从一个已证实的古地震遗址收集多旋回破裂历史，该地点位于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。圣安德烈亚斯断层南部只有4个地点的破裂年代学至少有5次事件。其中一个遗址是卡里佐平原的比达特扇。卡里佐平原是研究SAF破裂历史的最佳地点之一，因为它有经过证实的古地震记录，具有出色的滑移率和逐次滑动测量，并且有可能通过增加地震记录的长度来显著扩大数据集。Bidart Fan之前的工作表明，它包含了一份冗长的、可断代的地表破裂记录。在Bidart Fan上的苏丹武装部队地区共挖掘了四条战壕。这些海沟产生了一个综合年代学，由过去3000年来比达特扇形的10个地表破裂组成。最近的5次地震的年代相当准确，但之前5次地震的日期的不确定性要大得多。因此，这五次早期地震是这一项目的主要目标。在Bidart Fan上放置的额外沟渠揭示了更好的跨风扇沉积的空间和时间记录，从而改善了以前记录的地震的日期。样品的放射性碳测年将从加州大学获得，欧文新的凯克加速器质谱仪致力于碳同位素，使用劳伦斯·利弗莫尔国家实验室在古地震学中应用放射性碳测年的改进。该项目包括一项类似的努力，以改善卡里佐平原的活动记录。它将卡里佐平原地表破裂的时间记录增加了一倍，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一个主要古地震地点。

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.