The 1994 Northridge Earthquake and Prediction of Ground Motions on the Hanging Walls and Foot Wall of Thrust Events

9416451萨默维尔这项研究的目的是利用1994年北岭地震和其他逆冲地震的强震数据，建立一个经验模型来预测逆冲断层周围的地面运动，包括上盘和脚壁上的地面运动的差异。众所周知，在倾斜断层的上盘上，地面运动比在下盘上要大得多。在1994年北岭地震的地面运动中观察到了这一点，位于北岭断裂上盘的圣费尔南多山谷北部的峰值加速度大于位于北面圣加布里埃尔山脉的山脚边等距离处记录的峰值加速度。北岭地震的峰值加速度比目前的经验衰减关系预测的要大得多(例如，在距离小于30公里的地方，峰值加速度大了40%-50%)，即使考虑到推覆事件预计的20%-30%的大运动。了解北岭地震的地面运动是否代表北岭地震的地面运动是否代表未来推覆和/或盲冲地震中预期的地面运动，对于建立经验地震动衰减关系和修订抗震建筑规范具有重要的意义。该项目使用1994年北岭地震和其他地震的强震数据来量化地震机制对周期为0至4秒、距离为0至50公里、震级为6至7.5级的水平和垂直反应谱的影响。它使用了对逆冲和斜向地震记录的运动进行的经验分析，并辅之以数值模拟。这两种方法相辅相成，将产生比单独使用任何一种方法所产生的更强劲的结果。断层类型系数的经验模型考虑了地震机制作用的距离和震级相关性，以及上盘和下盘地面运动的差异。地震动数值模拟是为了帮助理解地震机制对地面运动影响的原因，并指导回归分析中函数形式的选择，以建立经验模型。它允许单独测试各种条件的影响，例如场地在上壁或脚壁上的位置、破裂深度、应力降和破裂方向性。数值模拟还被用来评估北岭地震的地面运动是否总体上是推覆事件的异常，特别是对于盲冲事件，或者它们是否代表了未来推覆和/或盲冲地震中预期的地面运动。***

9416451 Somerville The objective of this study is to develop an empirical model for the prediction of ground motions around thrust faults, including differences between ground motions on the hanging wall and the foot wall, using strong motion data from the 1994 Northridge earthquake and other thrust earthquakes. Ground motions are known to be significantly larger on the hanging wall than on the foot wall of dipping faults. This was observed in the ground motions of the 1994 Northridge earthquake, where the peak accelerations in the northern San Fernando Valley, which lies on the hanging wall of the Northridge rupture, were larger than those recorded at equivalent distances on the foot wall side, which lies in the San Gabriel Mountains to the north. The peak accelerations from the Northridge earthquake were much larger (e.g. 40-50% larger at distances less than 30 km)than predicted by current empirical attenuation relations, even accounting for the 20-30% larger motions expected for thrust events. Knowing whether or not the ground motions from the Northridge earthquake are representative of ground motions from the Northridge earthquake are representative of ground motions expected in future thrust and/or blind thrust earthquakes has important implications for the development of empirical ground motion attenuation relations, and on the revision of seismic building codes. The project uses strong motion data from the 1994 Northridge earthquake and other earthquakes to quantify the effect of earthquake mechanism on horizontal and vertical response spectra for periods of 0 to 4 seconds, distances of 0 to 50 km, and magnitudes of 6 to 7.5. It uses an empirical analysis of recorded motions from thrust and oblique earthquakes, supplemented by numerical modeling. These two approaches compliment each other and will lead to more robust results than would result from using either approach by itself. The empirical model for the style-of-faulting factor considers the distance and magnitude dependence of the effect of earthquake mechanism as well as differences between ground motions on the hanging wall and foot wall. Numerical ground motion modeling is used to help understand the causes for the effect of earthquake mechanism on the ground motions and to guide the selection of the functional form used in the regression analysis to develop the empirical model. It permits the influences of various conditions, such as location of the site on the hanging wall or on the foot wall, the depth of rupture, stress drop, and rupture directivity to be tested separately. Numerical modeling is also used to evaluate whether the ground motions from the Northridge earthquake, which are larger than predicted by existing ground motion attenuation relations for thrust earthquakes, are anomalous for thrust events in general, and for blind thrust events in particular, or if they are representative of ground motions expected in future thrust and/or blind thrust earthquakes. ***