Collaborative Research: Spatial and Temporal Evolution of an Active Blind-Thrust Fault from Inception to the Most Recent Earthquake

该研究项目的重点是通过对逆冲断层系统上方发育的褶皱进行地质和地球物理调查，破译逆冲断层系统的古地震记录。在盲冲断层的情况下，这些与断层有关的褶皱提供了下伏断层上的古地震活动的唯一可辨别的记录，而地表褶皱陡坎本身就存在潜在的重大地表变形危险。来自哈佛大学和南加州大学的科学家们正在研究加州洛杉矶盆地活跃的普恩特山盲冲断层上方的一系列埋藏褶皱陡坎，以确定它们如何限制过去的地震历史。该方法包括分析石油工业反射数据，采集多尺度、高分辨率地震反射图像，挖掘详细的钻孔断面，以记录和直接采样最年轻的褶皱地层。地震反射和钻孔数据将在该断层系统的所有三个区段上收集，从而有助于对断层系统行为进行全面分析。此外，为了阐明在过去大约100，000年中褶皱生长和断层滑动速率的相对恒定性，将在Puente Hills盲冲断层的西部、洛杉矶段上方的明确生长地层中直接钻出一个深（约220米深）的连续取芯钻孔。总的来说，这些数据将有助于确定地震中发生的褶皱成分，盲冲系统的各个部分如何在许多破裂周期中相互作用，以及这些断层上的滑动速率如何在不同的时间尺度上变化，从地震周期到数百万年。以及开发更好的评估区域地震危险的方法。普恩特山盲断层位于大都市洛杉矶的心脏地带，由于其规模和位置，它是美国最严重的确定性地震灾害之一。这项研究将有助于确定该断层未来地震的可能震级和频率，从而提高对区域地震灾害的认识。此外，通过这项研究开发的方法将被证明是容易出口的，从而作为一种工具，以了解更多关于世界各地的潜在危险故障。

This research project is focused on deciphering paleo-earthquake records for thrust faults systems through geological and geophysical investigations of folds that develop above them. In the case of blind-thrust faults, these fault-related folds provide the only discernable record of paleo-earthquake activity on the underlying faults, and surface fold scarps in their own right present a potentially significant surface deformation hazard. Scientists from Harvard University and University of Southern California are examining a series of buried folds scarps above the active Puente Hills blind-thrust fault in the Los Angeles basin, California, to determine how they constrain past earthquake histories. The approach involves analysis of petroleum-industry reflection data, acquisition of multi-scale, high-resolution seismic reflection imagery, and excavation of detailed borehole transects to document and directly sample the youngest folded strata. Seismic reflection and borehole data will be collected above all three segments of this fault system, thus facilitating a comprehensive analysis of fault system behavior. Moreover, to elucidate the relative constancy of fold growth and fault slip rate over the past approximately 100,000 years, a deep (about 220 meters deep) continuously cored borehole will be drilled directly into the well-defined growth strata above the western, Los Angeles segment of the Puente Hills blind-thrust fault. Collectively, these data will help define what components of folding occur seismically, how various segments of a blind-thrust system interact over many rupture cycles, and how slip rates on these faults vary over different time scales, ranging from seismic cycles to millions of years.The motivations for this study are to understand the fundamental mechanism of blind-thrust faulting and folding, as well as to develop better methods of assessing regional earthquake hazards. The Puente Hills blind thrust underlies the heart of metropolitan Los Angeles and, because of its size and location, represents one of the worst deterministic seismic hazards in the United States. This study will help define the likely magnitude and frequency of future earthquakes on this fault, thereby improving the understanding of regional earthquake hazards. Moreover, the methodology developed through this study will prove readily exportable and thus serve as a tool to learn more about potentially dangerous faults around the world.