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混杂的全局最优化算法是一种模拟退火法和下坡的单纯形法相结合的方法,该法用来反演远震体波求解震源参数。在时间域对震源时间函数加约束、反演双力偶参数而不是反演矩张量元素以及考虑多重震源导致非线性和多重模型问题,在这些问题中,目标函数包括许多局部极小值。传统的线性化方法和最小二乘迭代的方法,依赖于初始模型和多重震源的处理顺序,并且可能收敛于一个局部的极小值。此外,格点搜索方法对于我们要同时处理的参数数量来说,也是不实用的。混杂的全局方法提供了另一有吸收力的方法,因为该法可收敛到预先规定的目标函数的全局极小值上去,并可用来同时反演多重震源。如果需要的话,很易将模型参数约束加到全局搜索过程中来。本文用1992年加州兰德斯地震的多点源参数模型作为反演方法的一个实例。该地震的破裂是沿着三个主断层段发生的:约翰逊谷断层、霍姆斯特德断层和埃默森/罗克河断层。我们反演了每个震源的走向、倾角和滑动角、震源时间间隔以及远场震源时间函数。反演中得到的参数与现场观测到的和其它的研究结果是一致的。断层走向与地面破裂走向的变化非常一致。断层倾角沿整个破裂长度接近90°,且几乎是纯右旋走向滑动。估计的地震矩是7.6×10~(26)dyne-cm。在霍姆斯特德断层和埃默森断层的交叉点,地震矩的释放连续性表明,这两个断层在深处比在地面可能更连续。在从约翰逊谷断层到霍姆斯特德断层的过渡区,地震矩释放是复杂的,表明断层活动有一个复杂的时间历程,并且与所绘的早期断层之间没有什么直接关系。
A hybrid global optimization algorithm is a combination of simulated annealing and downhill simplex method, which is used to invert teleseismic body waves to solve hypocenter parameters. Constraining the source time function in the time domain, inverting the dual couple parameters instead of inverting the moment tensor elements, and considering multiple sources lead to nonlinear and multiple model problems in which the objective function includes many local minima. The traditional methods of linearization and least-squares iteration depend on the processing order of the initial model and the multi-source, and may converge to a local minimum. In addition, the grid search method is impractical for the number of parameters we want to process simultaneously. A hybrid global approach offers another attractive approach because the method converges to a pre-defined global minimum of the objective function and can be used to simultaneously retrieve multiple sources. If necessary, it is easy to add model parameter constraints to the global search process. In this paper, a multi-point source parameter model of the 1992 Landers earthquake in California is taken as an example of the inversion method. The earthquake ruptured along three main fault sections: the Johnson Valley fault, the Homestead fault and the Emerson / Rock River fault. We inverted the strike, dip and slip angle of each source, the focal time interval and the far-field focal time function. The parameters obtained in the inversion are consistent with those observed in the field and other studies. The trend of faults is very consistent with the change of the direction of ground rupture. The fault dip angle is close to 90 ° along the entire rupture length and is almost purely right-lateral slip. The estimated seismic moment is 7.6 × 10 ~ (26) dyne-cm. The continuity of seismic moment release at the intersection of the Homestead and Emerson faults suggests that the two faults may be more continuous at depth than at the ground. The release of seismic moment is complex at the transition from the Johnson Valley fault to the Homestead fault, indicating that the fault activity has a complex time history and is not directly related to the early fault plotted.