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断层行为来回答。古地震调查提供了断层部分多旋回破裂史的资料。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模型的基础。圣安德烈亚斯断层的高滑动率、短重复周期、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。该项目包括在世界上科学上最重要和最危险的断层之一：圣安德烈亚斯断层沿线的一个已证实的古地震地点收集多周期破裂历史。沿着南圣安德烈亚斯断层，只有4个地点有至少5次断裂事件的破裂年表。其中一个地点是卡里佐平原的比达特扇。Carrizo平原是研究SAF断裂历史的最佳地点之一，因为它有一个经过验证的古地震记录，具有出色的滑动率和每事件滑动量，并且有可能通过增加地震记录的长度来显着扩大数据集。先前在比达特扇上的工作表明，它包含了一个冗长的、可确定数据的地表破裂记录。在比达特扇上的SAF区共开挖了四条沟。这些海沟产生了一个复合年表，包括比达特扇在过去3000年里的10次表面破裂。最近的5次地震的年代相当准确，但前5次破裂的年代的不确定性要大得多。因此，这五次早期地震是本项目的主要研究对象。在比达特扇上放置的其他海沟揭示了扇上沉积的更好的时空记录，从而改进了先前记录的地震日期。样品的放射性碳年代将从加州大学欧文分校的新凯克加速器质谱设备获得，该设备致力于碳同位素，使用劳伦斯利弗莫尔国家实验室改进的放射性碳定年法在古地震学中的应用。这个项目包括一个类似的努力，以改善卡里佐平原的事件记录。它将卡里佐平原地表破裂的时间记录翻了一番，并在圣安德烈亚斯断层上提供了一个主要的古地震地点，用于开发和测试断层行为模型。

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.