2024 年 12 巻 2 号 論文ID: 24-17054
On November 22, 2016, a magnitude (MJMA) 7.4 intraplate normal-fault earthquake with the tension axis in the northwest–southeast direction occurred off Fukushima Prefecture, Japan (2016 off-Fukushima earthquake). However, north–south oriented reverse fault-type earthquakes were assumed for this region by the tsunami database, which contains the precalculated tsunami data used for real-time tsunami forecasting by the Japan Meteorological Agency (JMA). According to our previous study, among the differences in the earthquake mechanism between that assumed in the tsunami database and that of the 2016 off-Fukushima earthquake, while the misforecast between the normal and reverse faults did not affect the real-time tsunami forecast, the difference in the strike angle of the fault plane was the main cause of the underestimated height forecast for Miyagi Prefecture. Based on the concept that an efficient scenario arrangement can be achieved when differences in forecasts from adjacent scenarios in the tsunami database are similar, and the results from sensitivity analyses of the tsunami height distribution to fault parameters for the 2016 off-Fukushima earthquake, it is reasonable to add tsunami scenarios with different fault plane strikes angles and the same simulation point near the epicentral area. We compared the centroid moment tensor solutions for earthquakes of moment magnitude 5.5 or more that occurred in coastal areas around Japan with the fault parameters assumed in the tsunami database. We then added scenarios to the tsunami database for areas where the difference in strike angles was 30° or more. Our performance tests using past scenarios indicate that the underestimation of tsunami warnings for the 2016 off-Fukushima earthquake can be avoided by using the modified database and that new scenarios will be frequently referenced in future tsunami warning operations. The modified tsunami database has been used for real-time tsunami warning operation by JMA.
