10:45 AM - 12:15 PM
[HDS06-P15] Probabilistic Tsunami Hazard Assessment Integrating 5 regions in Japan : Probability Setting Method and Hazard Assessment Results
Keywords:Probabilistic tsunami hazard assessment, Nankai Trough, Kuril Trench, Japan Trench, Sagami Trough, Ryukyu Trench
In the seas surrounding Japan, tsunamis have been repeatedly generated by huge earthquakes associated with plate subduction. The Headquarters for Earthquake Research Promotion (ERP) defines such earthquakes as trench earthquakes and publishes long-term assessments of the areas where they occur, their magnitudes, probabilities, and so on. Specifically, the long-term assessments are for seismic activity along the Kuril Trench, the Japan Trench, the Sagami Trough, the Nankai Trough, and the Ryukyu Trench. In addition, the Earthquake Headquarters of Japan has published "Probabilistic Tsunami Hazard Assessment of Large Earthquakes Occurring along the Nankai Trough" as a probabilistic tsunami hazard assessment based on the long-term assessment. This tsunami assessment uses a probabilistic approach to evaluate the tsunami hazard at the coast for interplate earthquakes of M8 to M9 earthquake magnitude, excluding the largest class earthquakes. Dohi et al. (2022) evaluated the probability of earthquakes occurring along the Kuril Trench, the Japan Trench, the Sagami Trough, and the Nankai Trough, respectively, based on long-term assessments for each area, and conducted a probabilistic tsunami hazard assessment integrating them.
In this presentation, we group the inter-plate and intra-plate earthquakes in each sea area for which the location, magnitude, and probability of the next earthquake were evaluated by the Earthquake Headquarters, explain the probability settings for the probabilistic tsunami hazard assessment, and report the results of the hazard assessment. For the wave source fault models and tsunami propagation analysis for each earthquake group, please refer to Murata et al. In setting the probabilities for each sea area, we used "Long-Term Evaluation of Seismic Activity along the Kuril Trench (3rd Edition)" (ERP, 2017), "Long-Term Evaluation of Seismic Activity along the Japan Trench" (ERP, 2019), "Long-Term Evaluation of Seismic Activity along the Sagami Trough (2nd Edition)", (ERP, 2014), and "Nankai Trough Long-Term Assessment of Seismic Activity along the Nankai Trough (2nd Edition)" (ERP, 2013), and "Long-Term Assessment of Seismic Activity around the Ryukyu trench" (ERP, 2004), and targeted earthquake groups where the earthquake scale and average occurrence interval are mentioned and the impact of tsunami expected from the earthquake scale is not small. The study was conducted to evaluate the long-term evaluation of the earthquake activity. In this study, for the earthquakes whose magnitude was evaluated as M in the long-term evaluation, the magnitude was read as Mw, and for the tsunami earthquakes whose magnitude was evaluated as Mt, the amount of slip was calculated from Mt and Mw was calculated. When evaluating a continuous Mw range within a group of earthquakes, we considered that the earthquake size and frequency follow the Gutenberg-Richter (GR) law, and used a b value of 0.9 as the average value of the slope of the GR law for all of Japan. For earthquake groups for which the probability of occurrence was evaluated based on the long-term evaluation and for which the values of mean occurrence interval, elapsed time since earthquake, and BPT distribution variability were evaluated, the 30-year probability of occurrence (as of January 1, 2022) was obtained by an updated process based on the BPT distribution. For the other earthquake groups, the earthquakes were assumed to occur according to a steady-state Poisson process.
As an example, for the megathrust earthquake (17th-century type) that has been evaluated for a long period in the Kuril Trench, the wave source fault model was set up in the range of Mw 8.6 to 9.2, and the 30-year probability of occurrence was calculated based on the BPT distribution. 13.0% was used. The method of integrating the obtained hazard curves is, in principle, independent events for each sea area, independent events for earthquake groups in a certain sea area, independent events for seismic source regions in a certain earthquake group, and independent events for wave source fault models in a certain seismic source region. Hazard curve integration was carried out as an exclusive event.
An overview of the 30-year exceedance probability distribution map of the maximum water level rise of 3 m or more obtained from the estimation shows that some locations have a maximum probability of 70%, and the probability is more than 10% in a wide area along the Pacific coast.
In this presentation, we group the inter-plate and intra-plate earthquakes in each sea area for which the location, magnitude, and probability of the next earthquake were evaluated by the Earthquake Headquarters, explain the probability settings for the probabilistic tsunami hazard assessment, and report the results of the hazard assessment. For the wave source fault models and tsunami propagation analysis for each earthquake group, please refer to Murata et al. In setting the probabilities for each sea area, we used "Long-Term Evaluation of Seismic Activity along the Kuril Trench (3rd Edition)" (ERP, 2017), "Long-Term Evaluation of Seismic Activity along the Japan Trench" (ERP, 2019), "Long-Term Evaluation of Seismic Activity along the Sagami Trough (2nd Edition)", (ERP, 2014), and "Nankai Trough Long-Term Assessment of Seismic Activity along the Nankai Trough (2nd Edition)" (ERP, 2013), and "Long-Term Assessment of Seismic Activity around the Ryukyu trench" (ERP, 2004), and targeted earthquake groups where the earthquake scale and average occurrence interval are mentioned and the impact of tsunami expected from the earthquake scale is not small. The study was conducted to evaluate the long-term evaluation of the earthquake activity. In this study, for the earthquakes whose magnitude was evaluated as M in the long-term evaluation, the magnitude was read as Mw, and for the tsunami earthquakes whose magnitude was evaluated as Mt, the amount of slip was calculated from Mt and Mw was calculated. When evaluating a continuous Mw range within a group of earthquakes, we considered that the earthquake size and frequency follow the Gutenberg-Richter (GR) law, and used a b value of 0.9 as the average value of the slope of the GR law for all of Japan. For earthquake groups for which the probability of occurrence was evaluated based on the long-term evaluation and for which the values of mean occurrence interval, elapsed time since earthquake, and BPT distribution variability were evaluated, the 30-year probability of occurrence (as of January 1, 2022) was obtained by an updated process based on the BPT distribution. For the other earthquake groups, the earthquakes were assumed to occur according to a steady-state Poisson process.
As an example, for the megathrust earthquake (17th-century type) that has been evaluated for a long period in the Kuril Trench, the wave source fault model was set up in the range of Mw 8.6 to 9.2, and the 30-year probability of occurrence was calculated based on the BPT distribution. 13.0% was used. The method of integrating the obtained hazard curves is, in principle, independent events for each sea area, independent events for earthquake groups in a certain sea area, independent events for seismic source regions in a certain earthquake group, and independent events for wave source fault models in a certain seismic source region. Hazard curve integration was carried out as an exclusive event.
An overview of the 30-year exceedance probability distribution map of the maximum water level rise of 3 m or more obtained from the estimation shows that some locations have a maximum probability of 70%, and the probability is more than 10% in a wide area along the Pacific coast.