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

本文研究了1999年台湾（集集）MW7.6主震和大余震的运动学源过程，以及三维速度结构对强地震动产生的影响。集集地震发生在高度城市化地区，造成了相当大的破坏和人类痛苦，再次强调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提供了在前所未有的尺度上研究震源和波传播的机会。提出了三种不同几何形状的断层模型来描述集集地震中逆冲断层的运动学，并通过拟合观测和合成地震波形以及地面变形（GPS）数据进行了验证。通过对强运动和GPS数据集进行运动学反演，以确定断层滑动的最佳分布，对这些几何图形进行了测试。此外，几次大余震表现出浅倾或陡倾的逆震源机制。特别令人感兴趣的是，是否有余震实际上在低角度平面上滑动，这表明存在控制基底滑脱。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，从而获得活动断层表面的图像。台湾弧陆碰撞的造山活动导致了复杂的地壳结构，这在最近的层析成像研究和相当大的地形起伏中得到了证明。利用弹性、速度-应力交错网格有限差分算法，对主震和大余震的三分量地震波形、相位到达时间和峰值地震动参数进行建模，以约束三维波的传播和自由表面地形的影响。最后，分析了扩展有限故障源表示与三维结构耦合特性对模拟强运动波形的敏感性。本研究的结果将为未来的波形建模研究提供框架，以完善台湾的三维结构，并将为强地震动变率提供必要的检查，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.