Abstract
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) model. We then investigated the effects of our 3D CMT solutions on long-period ground motion simulations. Grid search CMT inversions were conducted using displacement seismograms for periods of 25–100 s. By comparing our 3D CMT solutions with those from the local one-dimensional (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 differences in the rigidity structures around the source regions between 3D and 1D velocity models. The 3D velocity structures (especially oceanic crust and mantle) are important for estimating seismic moments in intraslab earthquakes, which are related to fault size estimation. A detailed discussion for intraslab seismicity can be conducted using the 3D CMT catalog. The seismic moments also directly affect the amplitudes of ground motions. The 3D CMT catalog allows us to directly conduct the precise forward and inverse modeling of long-period ground motion without adjusting source models, which have been typically applied in the cases using the 1D CMT catalog. We also conducted long-period ground motion simulations using our 3D CMT solutions to evaluate the reproducibility of long-period ground motions at stations within the Kanto Basin. The simulations of our 3D CMT solutions well-reproduced observed ground motions for periods longer than 10 s, even at stations within the Kanto Basin. The reproducibility of simulations was improved from those using solutions in the 1D catalog.
Highlights
Long-period ground motions with predominant periods of 3-20 s have often been observed in large sedimentary basins and offshore regions
The centroid moment tensor (CMT) solutions based on displacement for periods longer than 20 s are generally considered robust against structural heterogeneities, compared to first-motion solutions (e.g., Takemura et al 2016)
As MeSOnet stations were densely deployed around the Tokyo metropolitan area in Japan, we evaluated long-period ground motion in the Kanto Basin using earthquakes that occurred after April 2017
Summary
Long-period ground motions with predominant periods of 3-20 s have often been observed in large sedimentary basins and offshore regions. To achieve precise forward and inverse modeling of long-period ground motions in the Kanto region, where large sedimentary basin and two subducting plates exist, accurate CMT solutions is required. The 3D CMT catalog allow us to directly conduct 3D ground motion simulations without adjusting source parameters, such as centroid depth, focal mechanism and seismic moment.
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