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

利用深钻孔数据确定加利福尼亚州洛杉矶普恩特山盲冲断层的地震潜力

• 批准号: 0920947
• 负责人: John Shaw
• 金额: $ 10.51万
• 依托单位: Harvard University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-01-15 至 2009-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0920947&HistoricalAwards=false
• 关键词: Defining; Earthquake; Potential; Puente; Hills

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.

该项目旨在了解盲逆冲断层和褶皱的基本机制，以及更好地评估区域地震危险性。其中一个关键目标是描述褶皱生长（因此断层滑动）随时间间隔的稳定性，该时间间隔比早期研究的浅井数据提供的时间间隔长，比深层石油工业地震反射数据分析提供的时间间隔短。一个220米深的井眼将穿过Puente Hills冲断带西部上方的活动褶皱轨迹，直接钻入高分辨率地震反射剖面中确定的特征。通过直接取样和确定主要反射体的年代，生长地层的几何形状以及已知的逆冲斜坡的几何形状可以用来确定大范围时间尺度内的滑动速率以及褶皱的隆升速率。从构造开始到最近的地震，抬升速率将被用来约束断层滑动速率。对断层滑动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害至关重要。结合断层相邻段的全新世古地震记录，将确定断层系统地震的大小和频率，为确定性地震危险性评估提供依据。到目前为止，这一断层段在很大程度上还没有被研究过，但由于它位于洛杉矶大都市高层地区的正下方，普恩特山逆冲是美国最大的决定性危险之一。