Michihiro Ohori

By Michihiro Ohori

This study sought to simulate strong broadband seismic motions beyond the corner frequencies used, for the same events, in previous studies. To correct discrepancies among the corner frequencies of events, a scaling law based on the ω−2 model was assumed and the spectral amplitude decay beyond the corner frequency was compensated. The observations were also corrected for location, focal mechanism, and time of occurrence. After estimating the empirical Green’s tensor spatial derivative (EGTD) from 11 aftershock events, using 0.2–10 Hz band-pass-filtered waveforms, the strong motion records for the mainshock and aftershocks were simulated. In the simulation of each event, the EGTD elements were multiplied by the moment tensor elements followed by summation and then corrected in their spectral amplitude taking the corner frequency of each event into account. At the closest epicentral distance, and for most events, an acceptable agreement was found between calculated and observed waveforms. The results were also compared with the outcomes of simulations using the empirical Green’s function method. As EGTD elements are determined by local underground structures, they could prove useful for future structural studies.

Part of the book: Earthquakes

By Michihiro Ohori, Yuri Masukawa and Keisuke Kojima

In Japan, compared with the Pacific coast, the Japan Sea coast has low seismicity and has experienced very few occurrences of historical tsunami damage. These characteristics lead to some difficulties in the promotion of disaster prevention education, because the Japan Sea coast has not often been threatened by earthquakes and tsunamis. In our study, focusing on the Hokuriku region in Japan, we conducted a tsunami simulation and examined the resulting tsunami hazard map. Three potential faults of Mw7.6 earthquake were selected to generate the tsunami. In addition, we calculated these three events with Mw7.8, given the inherent uncertainty in source parameters. Aside from tsunami height, arrival time, inundation height, and inundation area, we calculated the seismic intensity and the liquefaction occurrence rate by simplified methods. Our results indicated that Suzu City in Ishikawa Prefecture, located in the northeastern part of the Noto Peninsula, has a relatively high potential risk of tsunami as well as strong motion and liquefaction. Thus, Suzu City would represent a highly appropriate area in which to promote disaster prevention education in the Hokuriku region.

Part of the book: Natural Hazards