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研究了1992年兰德斯地震的破裂过程。采用了两步法以限定滑动幅度和破裂时间之间的相互影响,否则会影响仅用地震资料得到的解。首先用独立的大地测量资料来约束滑动分布及其不确定性,然后获取破裂传播的时间特征。第一步用干涉测量数据和全球定位系统测量数据进行独立反演和联合反演,以给出三段断层模型上沿走向和倾向的滑动分布特征。我们采用遗传算法来检验解的唯一性,并使用最小二乘找出拟合最佳的模型。根据大地测量的反演结果我们认为:用干涉测量数据足以给出兰德斯地震的滑动分布。由于在我们的构型中地表形变对浅层滑动比较敏感,因而所得到的地表滑动幅度比深层要高。得出的滑动分布与地表的地质观测结果一致,并证实了兰德斯地震的不均匀特征。霍姆斯特德谷断层(第2段)上绝大多数滑动发生在浅层,最大深度约为7 m。另一个滑动较大的区是在8 km 深的约翰逊谷断层上(第1段)。第二步则反演了强地面运动数据,使用了预设的最终滑动幅度和山大地测量数据推断的不确定性,对破裂过程的时间进程进行了约束。第二步强调地震随时间的强烈变化。高滑动区破裂前缘传播速度快,当破裂沿断层传播遇到阻力时其速度会减慢。平均而言,破裂前缘传播速度接近 S 波速度,并在开始后约20 s 结束。滑动幅度和破裂速度的较大变化表明:对破裂过程的描述用凹凸体的连续破裂比用匀速脉冲传播更为准确。
Studied the rupture process of the 1992 Landers earthquake. A two-step approach was used to limit the interaction between slip magnitude and fracture time, otherwise the solution obtained using seismic data alone would be affected. First, independent geodetic data are used to constrain the slip distribution and its uncertainty, and then obtain the time characteristics of rupture propagation. The first step is to perform independent inversion and joint inversion with the interferometric data and the GPS measurements to give the slip distribution along the strike and dip of the three-segment fault model. We use genetic algorithms to test the uniqueness of solutions and use least squares to find the best fit model. According to the inversion result of geodetic survey, we think that it is enough to give the slip distribution of Landes earthquake by using interferometric data. Because of the sensitivity of surface deformation to shallow sliding in our configuration, the resulting surface slide is much higher than in the deep. The resulting slip distribution is consistent with the surface geological observations and confirms the non-uniform characteristics of the Landes earthquake. Most of the slip in the Holmström fault (Section 2) occurs in the shallow depth with a maximum depth of about 7 m. Another area that is more slippery is the Johnson Valley fault that is 8 km deep (paragraph 1). The second step is to invert the strong ground motion data and use the default final slip amplitude and the inferred uncertainty of the mountain geodetic data to restrain the time course of the rupture process. The second step emphasizes the strong changes in earthquakes over time. The high slip zone ruptures the leading edge with a fast propagation velocity, which slows down as the rupture encounters resistance along the fault propagation. On average, the rupture front propagates near the S-wave velocity and ends approximately 20 s after the beginning. Larger changes in slip amplitude and fracture velocity indicate that the description of the rupture process is more accurate with continuous asperity bursts than with uniform velocity pulses.