Structural and Seismologic Investigation of Blind-thrust Earthquake Segmentation, San Joaquin Basin, California

通过对发生在加利福尼亚州中部圣华金盆地西部的1982年New Idria(Mw=5.4)、1983 Coalinga(Mw=6.5)和1985年Kettleman Hills(Mw=6.1)地震的综合地质和地震学分析，正在检验盲冲地震分段的性质。这些地震发生在New Idria、Coalinga和Kettleman Hills背斜之下，这些背斜形成了一个向南延伸到Lost Hills的梯队结构系统。同震抬升和地下研究的模式令人信服地证明，这些构造是与断层有关的褶皱，是对下伏的盲冲系统上的运动的响应而发展的。这三次地震的破裂区域的界限是由这个褶皱系统的明显的梯形偏移量来定义的，这种偏移量被认为覆盖在下伏的盲冲断层中的几何段边界上。褶皱具有良好的地表曝光性，地下结构由丰富的工业地震反射和测井数据确定。因此，这一地区是研究盲冲地震分段过程的绝佳机会，深入了解这一过程可以帮助评估其他活动逆冲区域的地震危险性。利用地震反射剖面、井控制、地表地质、遥感图像和精确重新定位的地震活动，描述了Lost Hills-Kettleman Hills-Coalinga褶皱和冲断链的几何和运动学特征。这项分析记录了在地震段边界上发生的撕裂(走滑)断层、侧向斜坡和其他类型的断层联系。对这些边界的断层几何形状的洞察将有助于开发一种更好的方法来确定其他盲冲系统上的潜在分段边界，这些边界通常决定地震的位置和强度，这是概率地震危险性评估中的两个关键参数。此外，这些详细的结构模型可以为盲冲事件中动态破裂传播和余震分布的数值研究提供一个很好的案例研究。此外，这些研究将提供一个地震构造模型，说明断层活动的速率和时间变异性，这可以与空间大地测量等更具区域性的测量以及包括圣安德烈亚斯在内的邻近断层系统的地震活动相比较。

The nature of blind-thrust earthquake segmentation is being examined through integrated geologic and seismologic analyses of the 1982 New Idria (Mw=5.4), 1983 Coalinga (Mw=6.5), and 1985 Kettleman Hills (Mw=6.1) earthquakes, which occurred in the western San Joaquin basin of central California. These earthquakes occurred beneath the New Idria, Coalinga, and Kettleman Hills anticlines, which form an en echelon system of structures that extend south to Lost Hills. Patterns of coseismic uplift and subsurface studies have demonstrated convincingly that these structures are fault-related folds that develop in response to motions on the underlying blind-thrust system. The limits of the rupture areas for the three earthquakes are defined by the distinct en echelon offsets of this fold system, which are thought to overlie geometric segment boundaries in the underlying blind-thrust fault. The folds have excellent surface exposures, and the subsurface structure is defined by a wealth of industry seismic reflection and well log data. Thus, this area presents an excellent opportunity to study processes of blind-thrust earthquake segmentation, insights into which can help to assess earthquake hazards in other regions of active thrusting.The geometry and kinematics of the Lost Hills - Kettleman Hills - Coalinga fold and thrust chain is characterized utilizing seismic reflection profiles, well control, surface geology, remote sensing imagery, and precisely relocated seismicity. The analysis is documenting the occurrence of tear (strike-slip) faults, lateral ramps, and other types of fault linkages at the earthquake segment boundaries. Insights into the fault geometries of these boundaries will translate into helping to develop a better methodology for defining potential segment boundaries on other blind-thrust systems, which often dictate the locations and magnitudes of earthquakes, two key parameters in probabilistic seismic hazard assessment. Moreover, these detailed structural models can provide a well-documented case study for numerical investigations of dynamic rupture propagation and aftershock distribution during blind-thrust events. Additionally, these investigations will provide a seismotectonic model that addresses the rates and temporal variability of fault activity, which can be compared to more regional measurements such as space geodesy and to earthquake activity on adjacent faults systems, including the San Andreas.