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Learning Past Disasters and Forecasting Future Earthquakes on the 100th Anniversary of the 1923 Kanto Earthquake

Description: 

The great Kanto earthquake occurred on September 1, 1923, and caused the worst earthquake disaster in Japan with ~105,000 casualties. The majority (~ 90 %) of victims were due to fire; a unique feature different from the 2011 Tohoku earthquake (>90 % by the tsunami) or the 1995 Kobe earthquake (~ 90 % by building collapse). The Kanto earthquakes (M ~8) occur along the Sagami trough, where the Philippine Sea plate subducts beneath the Kanto region. The penultimate Kanto earthquake, the 1703 Genroku earthquake, caused larger crustal deformation and worse tsunami disasters in the southern Boso peninsula. Recently, documents and tsunami deposits indicate that the 1293 Showo earthquake and the 1495 Meio earthquakes were also Kanto earthquakes, suggesting a recurrence interval of 210 +/- 9 years, while other candidates such as the 878 and 1433 earthquakes have been also pointed out.

In order to share such seismological knowledge and uncertainties with the general public, the Japanese government’s Earthquake Research Committee (ERC) annually estimates and announces long-term forecasts, in terms of occurrence probability in the next 30 years. The probability of a future Kanto earthquake is calculated as 2 % if Brownian Passage Model is adopted, while it is 10 % if the Poisson model is assumed. The ERC also makes National Seismic Hazard Maps, which are also accessed through the Japan Seismic Hazard Information Station (J-SHIS) website. The Central Disaster Management Council of the Cabinet Office makes damage estimation, assuming the worst-case scenario. When a 1923-type Kanto earthquake occurs, 700,000 to 1,330,000 houses may be burned and 20,000 to 70,000 people may be killed. For smaller (M~7) earthquakes beneath Tokyo, the fire damage may be up to 610,000 houses and the casualties may be up to 23,000 people. Because of the higher probability of occurrence (70 % in the next 30 years), the countermeasure policies were targeted to the latter scenario and shared with local governments and the general public.

Session: Collective Impact in Earthquake Science

Type: Oral

Date: 4/18/2023

Presentation Time: 08:00 AM (local time)

Presenting Author: Kenji Satake

Student Presenter: No

Invited Presentation: 

Authors