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

本研究项目的重点是通过对逆冲断层上发育的褶皱进行地质和地球物理调查，破译逆冲断层的古地震记录。在盲目逆冲断层的情况下，这些与断层相关的褶皱为下伏断层提供了唯一可识别的古地震活动记录，而表面褶皱陡坡本身就具有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目逆冲断层上方的一系列被掩埋的褶皱峭壁，以确定它们是如何限制过去的地震历史的。该方法包括分析石油工业反射数据，获取多尺度、高分辨率地震反射图像，以及挖掘详细的井眼断面，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部分上收集，从而便于对断层系统行为进行综合分析。此外，为了阐明在过去大约10万年中褶皱生长和断层滑动速率的相对稳定性，将在Puente Hills盲目逆冲断层洛杉矶西部段上方明确的生长地层上直接钻一个深（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褶皱的哪些组成部分在地震中发生，盲逆冲系统的各个部分如何在许多断裂周期中相互作用，以及这些断层的滑动率如何在不同的时间尺度上变化，从地震周期到数百万年。本研究的目的是为了了解逆冲断层和褶皱的基本机制，以及开发更好的区域地震危险性评估方法。普恩特山（Puente Hills）隐藏在洛杉矶大都会的中心地带，由于其面积和位置，它代表了美国最严重的确定性地震危险之一。这项研究将有助于确定该断层未来可能发生地震的震级和频率，从而提高对区域地震危险性的认识。此外，通过这项研究开发的方法将被证明很容易输出，从而作为一种工具，更多地了解世界各地潜在的危险断层。

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.