2025 Volume 25 Issue 4 Pages 4_37-4_50
In order to improve the accuracy of strong ground motion prediction, a propagation path attenuation model that depends on the apparent incident angle, which is derived from observational records, was introduced, and the effects on the calculated waves were investigated. The statistical Green's function method was used as the calculation method, and the results were compared with the conventional attenuation model. Assuming an M7-class fault as the source, we set up a strike-slip fault and a reverse fault model to calculate the seismic ground motion. In the case of the apparent incident angle dependent model, the effect of increasing the amplitude was observed directly above the fault distribution range, especially near the top of the asperity, and that the effect was small in other regions. In addition, the so-called hanging wall effect, in which the amplitude on the hanging wall side was increased in the reverse fault model, was observed, and the effect of the apparent incidence angle-dependent attenuation was suggested to further increase the amplitude in this area. These results suggest that the apparent incidence angle-dependent attenuation could be one factor to explain the large amplitude ground motion observed near seismic fault.
As described above, in the case of large earthquakes, it has been confirmed that the area where the increase in amplitude is significant due to the apparent incidence angle-dependent model does not extend over the entire area directly above the source fault, but may be limited to a narrower area depending on the position relative to the fault or asperity. It has also been suggested that in the case of reverse faults, the hanging wall effect and the amplitude increase effect due to the apparent incidence angle may overlap.
