March 9, 2021
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion
Ten years have passed since "the 2011 off the Pacific coast of Tohoku Earthquake" (hereinafter referred to as the Tohoku-Oki Earthquake) that caused, an unprecedented catastrophe, the Great Earthquake Disaster of East Japan, and we, the Earthquake Research Committee of the Headquarters for Earthquake Research Promotion, would like to express our deepest condolences to those who died in the disaster and extend our deepest sympathies to those who were affected by the earthquake. We sincerely pray for the reconstruction and development of the disaster area.
After the Great Hanshin-Awaji Earthquake Disaster that occurred in January 1995, the Special Measure Law on Earthquake Disaster Prevention was enacted in June, and based on this law the Headquarters for Earthquake Research Promotion was established in July of the same year. Since then, with the aim of strengthening earthquake disaster prevention measures, especially contributing to the reduction of damage caused by earthquakes, we have promoted earthquake research in Japan, and have been disseminating results such as the long-term evaluations to estimate the probability and scale of earthquakes that may occur in the future, and the national probabilistic seismic hazard maps.
The Tohoku-Oki Earthquake that occurred on March 11, 2011 was the largest earthquake with a magnitude (M) of 9.0 in the history of domestic observation. The Earthquake Research Committee had been conducting the long-term evaluations of subduction-zone earthquakes, etc. before the Tohoku-Oki Earthquake, but it had not been possible to evaluate M9 class super-giant subduction-zone earthquakes. In addition, regarding the tsunami that caused enormous damage, we did not evaluate it, although we had organized past cases.
Based on the lessons learned from the Tohoku-Oki Earthquake, the Earthquake Research Committee has made two major reviews on the way earthquake research had been conducted up to that point. One is the revision of the long-term evaluation of subduction-zone earthquakes and the improvement of the national probabilistic seismic hazard maps in consideration of the diversity of earthquakes and the uncertainty of information so that even super-giant earthquakes can be targeted. The other is the implementation of tsunami evaluation. In February 2013, the "Tsunami Evaluation Subcommittee" was established, and in January 2020, "Probabilistic Hazard Assessment of Tsunami due to Large Earthquakes along the Nankai Trough" was published.
On the other hand, the Headquarters for Earthquake Research Promotion has information on measures to convey the results of such earthquake research to the public and society in an easy-to-understand manner, and to raise awareness and measures for disaster prevention and mitigation in preparation for future earthquakes and tsunamis. However, we recognize that it is an issue that we must continue to strive for improvement. In addition, it has been pointed out that various data and analysis methods generated in the evaluation process can be used for earthquake resistance of buildings, but it cannot be said that they are being fully utilized. We recognize that it is necessary to provide the results that are easier to utilize so that the results of earthquake research will contribute to disaster prevention and mitigation in the future.
In addition, it is necessary to improve the evaluations conducted by the Earthquake Research Committee by incorporating the results of the latest earthquake research and the results of scientific and technological progress. At the same time, in order to utilize evaluations for disaster prevention measures of local governments and individual disaster prevention actions, it is necessary that we do not only modify hypotheses and models by incorporating academic research results, but also carefully consider their effects.
Ten years have passed since the Tohoku-Oki Earthquake, but the number of earthquakes in the aftershock area is higher than before the Tohoku-Oki Earthquake, and it will continue for the time being. Within the aftershock area, an M7.3 earthquake occurred within the Pacific Plate on the 13th of the last month, causing damage. On the other hand, in the long-term evaluation, the area along the Japan Trench, including the Pacific coast from offshore east of Aomori Prefecture to offshore Boso, is evaluated to have a high probability of large-scale earthquakes occurring between and within the plates. Based on these facts, it should be noted that large-scale earthquakes may occur in the aftershock area and its surroundings, including the inland area, and may be hit by strong shakings and high tsunamis over a long period of time.
In addition to the earthquakes along the Japan Trench, the long-term evaluation evaluates that there is a high probability that subduction-zone earthquakes that are expected to cause enormous damage, such as earthquakes along the Nankai Trough, earthquakes along the Kurile Trench, and earthquakes along the Sagami Trough, will occur. Inland earthquakes are smaller than subduction-zone earthquakes, but their epicenters are often shallow, and if they occur near urban areas, they are expected to cause great damage such as the 2016 Kumamoto Earthquake. In order to properly prepare for future earthquakes, the Earthquake Research Committee will sincerely endeavor to proceed with earthquake research while incorporating the latest technologies and knowledge, improve the dissemination of the results, and contribute to strengthening of earthquake disaster prevention measures.