[J02-1] Recent large earthquakes I

[J02-1-03] Ground motion simulation during the 2016 Kumamoto earthquake mainshock in near-fault area and Aso caldera

^○Kimiyuki Asano, Tomotaka Iwata (Disaster Prevention Research Institute, Kyoto Universiy, Uji, Kyoto, Japan)

We studied the strong ground motions caused by the heterogeneous rupture process during the mainshock of the 2016 Kumamoto earthquake sequence (Mj7.3). The source rupture process was analyzed using strong motion data, assuming a fault geometry along the Hinagu and Futagawa faults in accordance with the surface ruptures. We assigned point sources densely with an interval of 0.2 km on the assumed fault planes in order to reproduce appropriately near-fault ground motions, and estimated spatiotemporal slip at control points discretized with an interval of 1.8 km on the fault planes by the multiple time-window linear waveform inversion method (e.g., Hartzell and Heaton, 1983). The rupture started at a northwest-dipping fault plane along the Hinagu fault with almost pure right-lateral strike-slip, and continuously propagated across the junction of the Hinagu and Futagawa faults. Then, it propagated northeastward along the Futagawa fault, and stopped to rupture in the western part of the Aso caldera. The significant slip with 3-5 m including normal-slip component were observed on the Futagawa fault, and shallowest part has slip ranging from 1 to 2 m, which is consistent with surface rupture distribution. Strong ground motion time histories including significant coseismic displacement along the fault-parallel direction observed at two near-fault stations (Mashiki and Nishihara) were reproduced well by this source model. Significant fault-normal displacement with continuous cracks observed in the Aso valley area could be explained as lateral ground movement induced by the strong forward directivity pulse generated associated with the rupture on the Futagawa fault. We also conducted a 3D ground motion simulations up to 1 Hz using the 3D velocity structure model JIVSM (Koketsu et al., 2012) and the finite difference method to see the effect of the source rupture process including source directivity effects on the spatial variation in strong ground motions during this event.