Characterized source model of the M7.3 2016 Kumamoto earthquake by the 3D reciprocity GFs inversion with special reference to the velocity pulse at KMMH16

Abstract The 2016 Kumamoto earthquakes caused severe damage centering on the Mashiki residential area. velocity waveforms at station KMMH16 in Mashiki, during M 7.3 mainshock, show large pulses. We found that may be result of strong westward pulse. question raised is how near-fault ground motions with pulse were generated mainshock. focus characterized source model Strong Motion Generation Areas (SMGA). Empirical Green’s function (EGF) method widely used for modeling this case. However, case target site located just near fault nodal plane mechanism (like KMMH16), EGF event should perfectly fit which a rare Therefore, instead using EGFs, we theoretical 3D functions. Our approach nonlinear inversion. This requires calculation and comparison observations many models. To accelerate these calculations, use pre-calculated GFs by reciprocity JIVSM structure model. By aftershock records, validated periods as short 1.5 s. Target sites are limited to close fault: KMM005, KMM006, KMMH14, KMMH16. First, look an initial SMGA grid search applied relatively long-period (> 3 s) coarse parameters. Then, tune observed short-period simplex method. Necessary physical constraints range parameters here. important point our inversion scheme describe Kostrov-like slip functions inside each SMGAs two triangles. resulting agrees well other results. constructive interference pulses from SMGA1 SMGA2, Hinagu southwestern segment Futagawa fault. Graphical