11:45 AM - 12:00 PM
[HDS06-15] Integrated Probabilistic Tsunami Hazard Assessment for 5 subduction-zone earthquakes around Japan, based on long-term evaluation of japanese government
Keywords:tsunami, earthquake, exceedance probability, PTHA, long-term evaluation
We integrated the conditional probabilistic tsunami hazard assessment (cPTHA) for possible subduction-zone earthquakes included in "long-term evaluation(LTE) of earthquakes by Japanese government" along Kurile Trench, Japan Trench, Sagami Trough, Nankai Trough, and Ryukyu Trench.
cPTHAs for subduction-zone earthquakes were based on identification/ classification of earthquakes and their probability models of occurrence, documented in the respective LTEs; please refer to the respective previous studies(for the Kuril-Japan Trench, Hirata et al., 2022SSJ; Sagami Trough, Hirata et al.,2016SSJ; Nankai Trough, Hirata et al.,2019JpGU; Ryuyu Trench, Hirata et al., 2018SSJ). However, along Ryukyu Trench, excluding an area around Yonaguni Island, less information was available in LTE. In this case, a GR law is estimated from the regional seismicity and estimated PTHA using stationary Poisson process.
In the probabilistic integration, (i) in the case of earthquakes for which the uncertainty of earthquake magnitude and source geometry are pointed out in LTE (e.g., next great Nankai earthquake), different-source geometries, expressed as one of the uncertainty of the earthquake, are considered to be mutually exclusive, (ii) in other cases, different-source geometries are considered to be mutually independent (Ono et al.,this meeting).
The earthquake magnitude and number of source fault models considered in the present PTHA for each subduction-zone earthquakes are roughly as follows; (1) Kuril Trench + Japan Trench, Mw 7.6-9.2, >3700; (2) Sagami Trough, Mw 6.8-8.6, >1000; (3) Nankai Trough, Mw 7.7-9.0, >2700 (in the case of Nankai Trough, several earthquakes are assumed to occur simultaneously (within the same earthquake cycle), and the number of earthquake combination patterns is more than 340,000); (4) Ryukyu Trench, Mw7.0-9.4, >3,600 (Murata et al.,this meeting)
Spatial distribution of the 30-year excess probability (EP30) of tsunami (maximum water-level rise) exceeding 3 m at the coastline is: (1) along the coastal region from Cape Erimo to Kushiro in Hokkaido, and further to the Northern Four Islands, ranging from 20% to over 60% at maximum; (2) along the Pacific coast of Kanto and Tohoku regions, ranging from 10% as average to 30% at maximum; (3) along the Pacific coast of Shikoku and Wakayama prefectures, ranging from 20% to over 60% at maximum; (4) along Izu Peninsula coast with an average of 20% and 40% at maximum, and (5) along the Ryukyu Trench coast with an average of less than 10% (Dohi et al., JAEE,2020).
EP30 of (1) and (3) were evaluated to be high because the 30-year probabilities of occurrence (P30) of a possible giant earthquake off Hokkaido (17th century type), possible interpolate earthquakes off Nemuro and off Shikotan &Etorofu, and a giant earthquake off the Nankai Trough were 7-40%, ~70%, ~60%, and 70-80%, respectively. On the other hand, the reason for the relatively low EP30 of (2) for the Pacific coast of the Kanto and Tohoku regions is that it has been only a little more than 10 years since the off-the Pacific coast of Tohoku region occurred along the Japan Trench, and P30 is estimated as "almost 0%" in the LTE of Japanese government. This is considered to be due to the fact that the 30-year probability of occurrence is estimated to be "almost 0%" in LTE.
However, note that present integrated PTHA for the five subduction-zones reported in this study is nothing but a conditional PTHA that corresponds to "the case that the earthquake assessed in the LTE actually occurs as it did" and does not include the contribution of earthquakes that are not assessed in the long-term assessment.
This study was conducted as part of the research project "Research on Hazard and Risk Assessment" of the National Research Institute for Earth Science and Disaster Prevention (NIED).
cPTHAs for subduction-zone earthquakes were based on identification/ classification of earthquakes and their probability models of occurrence, documented in the respective LTEs; please refer to the respective previous studies(for the Kuril-Japan Trench, Hirata et al., 2022SSJ; Sagami Trough, Hirata et al.,2016SSJ; Nankai Trough, Hirata et al.,2019JpGU; Ryuyu Trench, Hirata et al., 2018SSJ). However, along Ryukyu Trench, excluding an area around Yonaguni Island, less information was available in LTE. In this case, a GR law is estimated from the regional seismicity and estimated PTHA using stationary Poisson process.
In the probabilistic integration, (i) in the case of earthquakes for which the uncertainty of earthquake magnitude and source geometry are pointed out in LTE (e.g., next great Nankai earthquake), different-source geometries, expressed as one of the uncertainty of the earthquake, are considered to be mutually exclusive, (ii) in other cases, different-source geometries are considered to be mutually independent (Ono et al.,this meeting).
The earthquake magnitude and number of source fault models considered in the present PTHA for each subduction-zone earthquakes are roughly as follows; (1) Kuril Trench + Japan Trench, Mw 7.6-9.2, >3700; (2) Sagami Trough, Mw 6.8-8.6, >1000; (3) Nankai Trough, Mw 7.7-9.0, >2700 (in the case of Nankai Trough, several earthquakes are assumed to occur simultaneously (within the same earthquake cycle), and the number of earthquake combination patterns is more than 340,000); (4) Ryukyu Trench, Mw7.0-9.4, >3,600 (Murata et al.,this meeting)
Spatial distribution of the 30-year excess probability (EP30) of tsunami (maximum water-level rise) exceeding 3 m at the coastline is: (1) along the coastal region from Cape Erimo to Kushiro in Hokkaido, and further to the Northern Four Islands, ranging from 20% to over 60% at maximum; (2) along the Pacific coast of Kanto and Tohoku regions, ranging from 10% as average to 30% at maximum; (3) along the Pacific coast of Shikoku and Wakayama prefectures, ranging from 20% to over 60% at maximum; (4) along Izu Peninsula coast with an average of 20% and 40% at maximum, and (5) along the Ryukyu Trench coast with an average of less than 10% (Dohi et al., JAEE,2020).
EP30 of (1) and (3) were evaluated to be high because the 30-year probabilities of occurrence (P30) of a possible giant earthquake off Hokkaido (17th century type), possible interpolate earthquakes off Nemuro and off Shikotan &Etorofu, and a giant earthquake off the Nankai Trough were 7-40%, ~70%, ~60%, and 70-80%, respectively. On the other hand, the reason for the relatively low EP30 of (2) for the Pacific coast of the Kanto and Tohoku regions is that it has been only a little more than 10 years since the off-the Pacific coast of Tohoku region occurred along the Japan Trench, and P30 is estimated as "almost 0%" in the LTE of Japanese government. This is considered to be due to the fact that the 30-year probability of occurrence is estimated to be "almost 0%" in LTE.
However, note that present integrated PTHA for the five subduction-zones reported in this study is nothing but a conditional PTHA that corresponds to "the case that the earthquake assessed in the LTE actually occurs as it did" and does not include the contribution of earthquakes that are not assessed in the long-term assessment.
This study was conducted as part of the research project "Research on Hazard and Risk Assessment" of the National Research Institute for Earth Science and Disaster Prevention (NIED).