Defining the Earthquake Potential of the Puente Hills Blind-Thrust Fault, Los Angeles, California with Deep Borehole Data

该项目旨在了解盲冲断层和褶皱的基本机制，以及更好地评估区域地震灾害。关键目标之一是表征褶皱增长（因此断层滑动）在时间间隔上的恒定性，该时间间隔长于早期研究的浅井数据所提供的时间间隔，并且短于深层石油工业地震反射数据分析所提供的时间间隔。在Puente Hills逆冲断层西部洛杉矶段上方的活动褶皱部位，将直接钻一个220米深的钻孔，进入高分辨率地震反射剖面图中确定的特征。通过直接对关键反射层进行采样和测年，生长地层的几何形状以及已知的逆冲斜坡几何形状可用于确定在很宽的时间尺度上的滑动速率以及褶皱的抬升速率。抬升速率反过来将被用来限制从构造形成到最近地震的断层滑动速率，对断层滑动速率的限制对于解释断层的活动水平以及通过定义应变积累和释放速率来量化地震危险性至关重要。结合断层相邻段全新世古地震记录，确定断层系统地震的规模和频度，作为确定性地震危险性评价的依据。迄今为止，该断层段基本上未被研究过，但由于其位置紧邻大都市洛杉矶的高层建筑区下方，普恩特山逆冲断层是美国最大的确定性灾害之一。

This project seeks to understand the fundamental mechanism of blind-thrust faulting and folding, as well as to better assess regional earthquake hazards. One of the key goals is the characterization of the constancy of fold growth (and therefore fault slip) over time intervals longer than those provided by shallow borehole data from earlier studies, and shorter than those provided by analysis of the deep, petroleum industry seismic reflection data. A 220-m-deep borehole across the locus of active folding above the western, Los Angeles segment of the Puente Hills thrust will be drilled directly into features identified in a high-resolution seismic reflection profile. By directly sampling and dating key reflectors, the geometry of the growth strata together with the known geometry of the thrust ramp can be used to determine slip rates over a wide range of time scales as well as the uplift rate of the fold. The uplift rate, in turn, will be used to constrain the fault slip rate from inception of this structure to the most recent earthquake.Constraints on fault slip rate are vital to interpreting the level of activity of the fault, and to quantifying earthquake hazards by defining strain accumulation and release rates. Combined with the Holocene record of paleo-earthquakes on the adjacent segment of the fault, this will define the size and frequency of earthquakes on the fault system, which will serve as the basis for deterministic seismic hazard assessment. This fault segment has heretofore been largely unstudied, but due to its location immediately beneath the high-rise district of metropolitan Los Angeles the Puente Hills thrust represents one of the largest deterministic hazards in the United States.