RUI: The Frazier Mountain Paleoseismic Site: Evaluation of Fault Behavior Models with Geologic Data from the Big Bend Section of the San Andreas Fault, CA

特征地震模型基于这样的观点，即随着时间的推移，断层上某一点的破裂段和地震位移是相当恒定的，因此所有的大地震在大小和范围上都是相似的。这一模型主导了圣安德烈亚斯断层的断层行为理论，因为它与历史数据的几个方面大体一致。然而，为了测试断层行为模型，需要长时间(1000年)的地震年龄和沿断层滑动的记录，但大弯附近古地震遗址大约200公里的空隙阻碍了圣安德烈亚斯断层南部地震的相关性。在这个项目中，阿巴拉契亚州立大学、俄勒冈大学和美国地质调查局之间的研究合作正在填补南加州弗雷泽山附近现场的这一空白。这项调查的目标是(1)将地震记录扩大到1000年以上，(2)通过详细的偏移层构造图确定每个事件的滑动，以及(3)建立一个结合传统放射性碳测年和古气候指标的年代地层框架，为不同地点之间的地震对比提供额外的时间属性。这些数据将有助于圣安德烈亚斯断层南部1500年来的地震破裂情景，以便与断层行为模型进行比较，并为小型研究增加一个数据集，这些研究允许测试地震复发模型，并比较不同时间尺度上的滑移率。尽管圣安德烈亚斯断层闻名于世，但人们对它知之甚少。例如，尽管有足够的数据预测未来30年圣安德烈亚斯断层南部发生6.7级以上地震的可能性约为59%，但断层将破裂的部分和将产生的滑动量是未知的，部分原因是现有的古地震记录存在空间差距。古地震学研究调查大地震产生的近期沉积物和偏移量，以确定过去地震的年龄和位移。这项研究将产生来自该空区的古地震数据，并将用于完善断层行为和地震复发的模型。由于这些模型支持联邦和州机构所要求的概率地震风险分析，并设定了保险费率、建筑规范和地震减灾资源的分配，因此添加这些关键数据将进一步科学地了解断层，并最终降低地震带来的社会风险。

The characteristic earthquake model is based on the idea that over time, rupture segments and earthquake displacements at a point along a fault are fairly constant so all large earthquakes are similar in size and extent. This model has dominated fault behavior theory for the San Andreas fault because it generally agrees with several aspects of historic data. However, to test fault behavior models, long (1000 year) records of earthquake ages and slip along a fault are needed but an approximately 200 km gap in paleoseismic sites near the Big Bend prevents correlation of earthquakes along the southern San Andreas fault. In this project, research collaboration between Appalachian State University, the University of Oregon and the U.S.Geological Survey is filling this gap at site near Frazier Mountain in southern California. The goals of this investigation are to (1) extend the record of earthquakes to greater than 1000 years, (2) determine slip per event by detailed structural mapping of offset layers, and (3) develop a chronostratigraphic framework that combines traditional radiocarbon dating with paleoclimate indicators to provides additional temporal attributes for correlating earthquakes between sites. These data will contribute to earthquake rupture scenarios for the past 1500 years along the southern San Andreas fault for comparison with fault behavior models and add a dataset to the small pool of studies that permit tests of earthquake recurrence models and comparison of slip rates on different time scales.Despite its fame, the San Andreas fault is poorly understood. For example, while sufficient data exist to forecast about a 59% chance of an earthquake larger than M6.7 on the southern San Andreas fault in the next 30 years, the portion of the fault that will rupture and the amount of slip that will be produced is unknown, in part due to a spatial gap in the available paleoseismic records. Paleoseismologic studies investigate recent deposits and offsets produced by large earthquakes to determine the age and displacement of past earthquakes. This study will result in paleoseismic data from this gap and which will be used to refine models of fault behavior and earthquake recurrence. Because these models underpin probabilistic seismic hazard analyses required by Federal and State agencies and which set insurance rates, building codes, and allocation of seismic hazard mitigation resources, adding this critical data will further scientific understanding of faults and ultimately reduce societal risk from earthquakes.