Long-period ground motions simulation using local 3D CMT inversion solutions in the Kanto region, Japan

Abstract:

In the region with strong structural heterogeneities, such as sedimentary basin and subducting oceanic plate, centroid moment tensor (CMT) inversion based on the one-dimensional (1D) structure model could provide incorrect solutions. In such regions, precise CMT solutions should be required for forward and inverse modeling of earthquake ground motions. We conducted centroid moment tensor (CMT) inversions of moderate (Mw 4.5–6.5) earthquakes in the Kanto region, Japan, using a local three-dimensional (3D) structure model. Based on wave propagation simulations using the 3D CMT solutions and various heterogeneous structure models, we then investigated the effects of our 3D CMT solutions on long-period ground motion simulations. We used the NIED F-net, and MeSO-net observed data. The simulations of evaluating Green’s functions and ground motions were conducted via the OpenSWPC (Maeda et al., 2017). The 3D CMT inversion method is described in Takemura, Okuwaki et al. (2020).

By comparing our 3D CMT solutions with those from the local 1D catalog, we found that our 3D CMT inversion systematically provides magnitudes smaller than those in the 1D catalog. The Mw differences between 3D and 1D catalogs tend to be significant for earthquakes within the oceanic slab. By comparing ground motion simulations between 1D and 3D velocity models, we confirmed that observed Mw differences could be explained by the differences in the rigidity structures between 3D and 1D velocity models. The typical 1D velocity model could not incorporate the 3D structure of subducting oceanic crust and mantle. We note that the seismic moments directly affect the amplitudes of ground motions. Thus, 3D CMT solutions are essential for the precise forward and inverse modeling of long-period ground motions. The simulations using our 3D CMT solutions well-reproduced observed ground motions for periods longer than 10 s, even at stations within the Kanto Basin.