2:30 PM - 2:45 PM
[HDS11-09] Probabilistic Tsunami Hazard Assessment based on the long-term evaluation for earthquakes along the Kuril and Japan trenches: Part 2
Keywords:tsunami, earthquake, PTHA, long-term evaluation
1. Introduction
The Earthquake Research Committee (ERC) of the Headquarters for Earthquake Research Promotion of the Japanese government, published a long-term evaluation (LTE) of subduction-zone earthquakes occurring around Japan. Hirata et al. (2022) presented an integrated probabilistic tsunami hazard assessment (PTHA) for earthquakes with magnitudes of approximately M7.8 or greater occurring along the Kuril and Japan trenches, as evaluated in the ERC's LTE (ERC, 2017, 2019). In this study, we presented an integrated PTHA for earthquakes with magnitudes of M7 or greater occurring along the Kuril and Japan trenches, evaluated in the LTE. This PTHA covers all earthquakes whose occurrence probability, occurrence area, and earthquake magnitude were evaluated/mentioned in the LTE, including earthquakes of approximately M7.8 or less that were not covered by Hirata et al. (2022).
2. Earthquake fault model
We constructed characterized earthquake fault models (CEFMs) of interplate and intraplate earthquakes and placed them in the seismogenic zone along the Kuril and Japan trenches evaluated in the LTE, using the 3D model of the subducting Pacific plate. A total of 7,357 CEFMs were constructed for earthquakes with magnitudes from Mw 7.0 to 9.2.
3. Tsunami propagation simulation
The initial water surface distribution was computed using methods described by Okada (1992) and Tanioka and Satake (1996). We computed tsunamis by solving nonlinear long-wave equations using the finite difference method, including run-up calculation, over a nesting grid system with a minimum grid size of 50 m to obtain 7,357 coastal tsunami height distribution patterns corresponding to 7,357 CEFMs. We obtained maximum tsunami heights at approximately 560,000 points on the coastline from Hokkaido to Okinawa (e.g., the Pacific coast, the coast of the Sea of Okhotsk, and the coast of the East China Sea).
4. Earthquake probability model
An earthquake probability model for the LTE, applied to each earthquake, was adopted. Regarding earthquakes whose magnitudes or occurrence areas were evaluated but occurrence probabilities were not mentioned in the LTE, we assumed that these earthquakes occurred following a stationary Poisson process and that the frequencies followed a G-R law with b=0.9.
5. Probabilistic integration
To probabilistically integrate the results of the tsunami propagation simulation for earthquakes along the Kuril and Japan trenches, respectively, we considered the following.
1) Earthquakes are considered to be mutually independent.
2-a) In the case of earthquakes for which the uncertainties of the occurrence area and source geometry are evaluated/mentioned in the LTE, different source geometries, expressed as one of the uncertainties of the earthquake, are considered mutually exclusive.
2-b) In other cases, different source geometries are considered to be mutually independent.
3) Different slip distribution patterns (CEFMs) are considered to be mutually exclusive.
6. Results of integrated PTHA
The figure shows the distribution of the 30-year exceedance probability (P30) of tsunami heights greater than 3 m. Along the Pacific coast from Cape Erimo to Kushiro in Hokkaido, and further to the Northern Four Islands, P30 ranged from 20% to over 60% at maximum. Along the Pacific coast of the Tohoku region, P30 ranged from approximately 10% to over 40%. Compared to Hirata et al. (2022), along the Pacific coast east of Cape Erimo, there was a difference of a few percent (approximately 10% at maximum) in P30; the P30 in this study tended to be generally higher.
The integrated PTHA in this study is a conditional PTHA that corresponds to the case in which the earthquake evaluated in the LTE occurred as expected. We plan to conduct an integrated PTHA, including the contribution of earthquakes that have not been evaluated in the LTE.
This study was conducted as part of the Research and Development on Hazard and Risk of Natural Disasters research project of the National Research Institute for Earth Science and Disaster Resilience (NIED).
The Earthquake Research Committee (ERC) of the Headquarters for Earthquake Research Promotion of the Japanese government, published a long-term evaluation (LTE) of subduction-zone earthquakes occurring around Japan. Hirata et al. (2022) presented an integrated probabilistic tsunami hazard assessment (PTHA) for earthquakes with magnitudes of approximately M7.8 or greater occurring along the Kuril and Japan trenches, as evaluated in the ERC's LTE (ERC, 2017, 2019). In this study, we presented an integrated PTHA for earthquakes with magnitudes of M7 or greater occurring along the Kuril and Japan trenches, evaluated in the LTE. This PTHA covers all earthquakes whose occurrence probability, occurrence area, and earthquake magnitude were evaluated/mentioned in the LTE, including earthquakes of approximately M7.8 or less that were not covered by Hirata et al. (2022).
2. Earthquake fault model
We constructed characterized earthquake fault models (CEFMs) of interplate and intraplate earthquakes and placed them in the seismogenic zone along the Kuril and Japan trenches evaluated in the LTE, using the 3D model of the subducting Pacific plate. A total of 7,357 CEFMs were constructed for earthquakes with magnitudes from Mw 7.0 to 9.2.
3. Tsunami propagation simulation
The initial water surface distribution was computed using methods described by Okada (1992) and Tanioka and Satake (1996). We computed tsunamis by solving nonlinear long-wave equations using the finite difference method, including run-up calculation, over a nesting grid system with a minimum grid size of 50 m to obtain 7,357 coastal tsunami height distribution patterns corresponding to 7,357 CEFMs. We obtained maximum tsunami heights at approximately 560,000 points on the coastline from Hokkaido to Okinawa (e.g., the Pacific coast, the coast of the Sea of Okhotsk, and the coast of the East China Sea).
4. Earthquake probability model
An earthquake probability model for the LTE, applied to each earthquake, was adopted. Regarding earthquakes whose magnitudes or occurrence areas were evaluated but occurrence probabilities were not mentioned in the LTE, we assumed that these earthquakes occurred following a stationary Poisson process and that the frequencies followed a G-R law with b=0.9.
5. Probabilistic integration
To probabilistically integrate the results of the tsunami propagation simulation for earthquakes along the Kuril and Japan trenches, respectively, we considered the following.
1) Earthquakes are considered to be mutually independent.
2-a) In the case of earthquakes for which the uncertainties of the occurrence area and source geometry are evaluated/mentioned in the LTE, different source geometries, expressed as one of the uncertainties of the earthquake, are considered mutually exclusive.
2-b) In other cases, different source geometries are considered to be mutually independent.
3) Different slip distribution patterns (CEFMs) are considered to be mutually exclusive.
6. Results of integrated PTHA
The figure shows the distribution of the 30-year exceedance probability (P30) of tsunami heights greater than 3 m. Along the Pacific coast from Cape Erimo to Kushiro in Hokkaido, and further to the Northern Four Islands, P30 ranged from 20% to over 60% at maximum. Along the Pacific coast of the Tohoku region, P30 ranged from approximately 10% to over 40%. Compared to Hirata et al. (2022), along the Pacific coast east of Cape Erimo, there was a difference of a few percent (approximately 10% at maximum) in P30; the P30 in this study tended to be generally higher.
The integrated PTHA in this study is a conditional PTHA that corresponds to the case in which the earthquake evaluated in the LTE occurred as expected. We plan to conduct an integrated PTHA, including the contribution of earthquakes that have not been evaluated in the LTE.
This study was conducted as part of the Research and Development on Hazard and Risk of Natural Disasters research project of the National Research Institute for Earth Science and Disaster Resilience (NIED).