摘要：We study two important aspects of the waveform moment tensor inversion for the shallow earthquakes in the subduction region: the effect of the intense lateral inhomogeneity in the structure, and the strategy to invert the waveform data for the focal mechanisms. For the first aspect, using a “ forward ” finite difference modeling, we demonstrate that the effect of the inhomogeneity is quite large on the surface waves with a period of about 20s, and the current knowledge on the subduction region structure is practically effective in reproducing the characteristics in the observed waveforms. For the second aspect, we develop a “ reciprocal ” moment tensor inversion method that can generate the Green’s functions for a large quantity of source locations (19,200 in this study) in a realistic inhomogeneous structure by only three finite difference calculations per a single station. The inversion with a grid search scheme result in a reasonable source location, moment tensor and fit of the waveforms using data from only two stations. The constraint on the epicenter in the “transverse” direction is found to be somewhat weak in the case of single-station inversions, but the two-station inversion improves the constraint.
