Ground Motion and Source Kinematics Studies of the 21 September 1999 Taiwan Earthquake

1999年9月21日台湾地震的地面运动和震源运动研究。研究了1999年台湾集集7.6级主震和大余震的运动学震源过程以及三维速度结构对强地面运动产生的影响。集集地震发生在一个高度城市化的地区，造成了相当大的破坏和人类痛苦，再次突出表明需要更好地了解控制强地面运动产生的过程。这次地震在数据质量和数量上都是独一无二的。400多个三分量强震台站记录了地震波，这一高质量的数据集为以前所未有的规模研究震源和波传播提供了机会。三个断层模型，每个具有不同的几何形状，已被提出来描述在集集地震逆冲断层的运动学，并通过拟合观测和合成的地震波形和地面变形（GPS）数据进行测试。这些几何形状进行测试，通过执行运动学反演的强震和GPS数据集，以确定最佳分布的断层滑动。此外，几个大的余震表现出浅或陡倾斜的反向震源机制。特别令人感兴趣的是，是否有任何余震实际上在低角度平面上滑动，表明存在控制性基底滑脱。通过研究主震和大余震的震源运动学，可以绘制地震序列的滑动分布图，从而获得活动断层面的图像。台湾岛弧-大陆碰撞造山活动导致了复杂的地壳结构，如最近的层析成像研究和相当大的地形起伏证明。三分量地震波形，相位到达时间，峰值地面运动参数的主震和大余震进行建模，以约束三维波的传播，和自由表面地形的影响，使用弹性，速度应力交错网格，有限差分算法。最后，由于扩展的有限断层源表示和三维结构的耦合性质的模拟强震波形的灵敏度进行了分析。这项研究的结果将形成未来的波形建模研究的框架，以完善台湾的三维结构，也将提供一个重要的检查强地面运动的变化，有助于美国的地震减灾工作。

Ground Motion and Source Kinematics Studies of the 21 September 1999 Taiwan EarthquakePI: Douglas S. DregerProposal EAR-0105998The kinematic source process of the 1999 MW7.6 Taiwan (Chi-Chi) mainshock and large aftershocks, and the effects of three-dimensional velocity structure on the generation of strong ground motions are investigated. The Chi-Chi earthquake, which occurred in a heavily urbanized region, inflicted considerable damage and human suffering once again underscoring the need for better understanding of the processes that control the generation of strong ground motions. This earthquake is unique in terms of data quality and quantity. More than 400 three-component strong motion stations recorded the earthquake waves, and this high quality data set provides an opportunity to study the earthquake source and wave propagation at scales never before possible. Three fault models, each with a distinct geometry, have been proposed to describe the kinematics of thrust faulting in the Chi-Chi earthquake, and are being tested by fitting observed and synthetic seismic waveforms and ground deformation (GPS) data. These geometries are tested by performing kinematic inversions of the strong motion and GPS data sets to determine the optimal distribution of fault slip. Additionally, several large aftershocks exhibited either shallowly or steeply dipping reverse focal mechanisms. Of particular interest is whether any of the aftershocks actually slipped on the low angle planes indicating the presence of a controlling basal decollement. By investigating the source kinematics of the mainshock and the large aftershocks it is possible to map the slip distribution of the earthquake sequence thereby obtaining an image of the active fault surface. The active mountain building of the Taiwan arc-continent collision has resulted complex crustal structure, as evidenced in recent tomographic studies and the considerable topographic relief. Three component seismic waveforms, phase arrival times, and peak ground motion parameters for the mainshock and large aftershocks are being modeled to constrain the three-dimensional wave propagation, and effects of free-surface topography using an elastic, velocity-stress staggered-grid, finite difference algorithm. Finally, the sensitivity of simulated strong motion waveforms due to the coupled nature of extended finite-fault source representations and three-dimensional structure is being analyzed. The results from this study will form the framework for future waveform modeling studies to refine the 3D structure of Taiwan, and will also provide an essential examination of strong ground motion variability contributing to the US earthquake hazard mitigation effort.