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

特征地震模型是基于这样一种观点，即随着时间的推移，断层某一点上的破裂段和地震位移是相当恒定的，因此所有大地震的规模和范围都是相似的。该模型在圣安德烈亚斯断层的断层行为理论中占主导地位，因为它与历史数据的几个方面基本一致。然而，为了测试断层行为模型，需要长时间（1000年）的地震年龄和断层滑动记录，但是在大弯曲附近的古地震地点大约有200公里的间隙，阻止了沿南部圣安德烈亚斯断层的地震相关。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填补了南加州弗雷泽山附近的这一空白。本研究的目标是：(1)将地震记录扩展到1000年以上；(2)通过对偏移层进行详细的构造测绘来确定每次地震的滑动量；(3)建立一个年代地层框架，将传统的放射性碳定年法与古气候指标相结合，为不同地点之间的地震关联提供额外的时间属性。这些数据将有助于研究过去1500年沿着南圣安德烈亚斯断层的地震破裂情景，以便与断层行为模型进行比较，并为小型研究库添加一个数据集，以便测试地震复发模型和比较不同时间尺度上的滑动率。尽管声名远扬，人们对圣安德烈亚斯断层却知之甚少。例如，虽然有足够的数据可以预测在未来30年内，南圣安德烈亚斯断层发生6.7级以上地震的概率约为59%，但断层破裂的部分和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。古地震学研究调查最近的沉积物和大地震产生的偏移，以确定过去地震的年龄和位移。这项研究将从这个缺口得到古地震数据，并将用于改进断层行为和地震复发的模型。由于这些模型是联邦和州机构要求的概率地震灾害分析的基础，并制定了保险费率、建筑规范和地震灾害减灾资源的分配，增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.