Abstract In this study, the gravity changes observed by GRACE satellites along with the deformation field determined from GPS velocity vectors are used to estimate the fault parameters of 2004 Sumatra-Andaman Earthquake (SAE) by the inversion of PSGRN/PSCMP dislocation model. To do so, the co-seismic gravity changes are determined by fitting a time-series function to the GRACE monthly gravity fields and the effects of hydrology are suppressed with the aid of Global Land Data Assimilation (GLDAS) model. To increase the accuracy of inversion process, the GPS observed co-seismic and post-seismic displacements from 90 stations scattered across the deformed area are also used to constrain the inversion algorithm. The inversion is performed via the Particle Swarm Optimization (PSO) method that minimizes the error between the model-predicted and observed deformation and gravity changes. To this end, the PSGRN/PSMCP dislocation model predicts the deformation and gravity changes for each candidate fault in the PSO iterative process. It is shown that the joint use of the GPS and GRACE data in determination of focal mechanism, results in a fault model that is better consistent with the geometry of the existing subduction zone compared to the inverted fault using only GPS or GRACE data. Due to the complex geometry of the Sunda Trench, a discretized rectangular fault system is considered that allows the depth, slip, strike angle and dip angle vary between the sub-faults. In fact, the estimated fault model consists of 100 sub-faults with a total moment magnitude of Mw = 9.23 that matches the curved geometry of the Sunda Trench. The fault model reveals that the slip has a greater magnitude in segments near the northern Sumatra and Nicobar islands while for the segments of the fault, near the Andaman Islands, the slip is relatively smaller and has its greater magnitudes at depth. The depths and dip angles of the estimated fault model are compared to the SLAB2 3D geometry provided for the Sumatra and Java subduction zones and through this comparison, the RMSEs of 6.0 km for the depth and 3.1 ° for the dip angle are obtained.

中文翻译：

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GPS变形场和GRACE重力变化联合反演2004年苏门答腊大地震的震源机制

摘要 本研究利用GRACE卫星观测到的重力变化以及GPS速度矢量确定的形变场，通过PSGRN/PSCMP位错模型反演，估计2004年苏门答腊-安达曼地震(SAE)的断层参数。为此，通过将时间序列函数拟合到 GRACE 月重力场来确定同震重力变化，并借助全球土地数据同化 (GLDAS) 模型抑制水文的影响。为了提高反演过程的准确性，还使用 ​​GPS 观测到的分布在变形区域的 90 个站点的同震和震后位移来约束反演算法。反演是通过粒子群优化 (PSO) 方法执行的，该方法可最大限度地减少模型预测和观察到的变形和重力变化之间的误差。为此，PSGRN/PSMCP 位错模型预测了 PSO 迭代过程中每个候选断层的变形和重力变化。结果表明，与仅使用 GPS 或 GRACE 数据的倒置断层相比，联合使用 GPS 和 GRACE 数据确定震源机制，导致断层模型更符合现有俯冲带的几何形状。由于巽他海沟的复杂几何形状，离散的矩形断层系统被认为允许子断层之间的深度、滑动、走向角和倾角变化。实际上，估计的断层模型由 100 个子断层组成，总力矩大小为 Mw = 9.23，与巽他海沟的弯曲几何形状相匹配。断层模型表明，在靠近苏门答腊岛和尼科巴岛北部的断层段中，滑动幅度较大，而在安达曼群岛附近的断层段，滑动幅度相对较小，并且在深度处具有较大的幅度。将估计断层模型的深度和倾角与为苏门答腊和爪哇俯冲带提供的 SLAB2 3D 几何形状进行比较，通过这种比较，获得深度为 6.0 公里和倾角为 3.1°的 RMSE。断层模型表明，在靠近苏门答腊岛和尼科巴岛北部的断层段中，滑动幅度较大，而在安达曼群岛附近的断层段，滑动幅度相对较小，并且在深度处具有较大的幅度。将估计断层模型的深度和倾角与为苏门答腊和爪哇俯冲带提供的 SLAB2 3D 几何形状进行比较，通过这种比较，获得深度为 6.0 公里和倾角为 3.1°的 RMSE。断层模型表明，在靠近苏门答腊岛和尼科巴岛北部的断层段中，滑动幅度较大，而在安达曼群岛附近的断层段，滑动幅度相对较小，并且在深度处具有较大的幅度。将估计断层模型的深度和倾角与为苏门答腊和爪哇俯冲带提供的 SLAB2 3D 几何形状进行比较，通过这种比较，获得深度为 6.0 公里和倾角为 3.1°的 RMSE。