How to obtain probabilities and scenarios of a large earthquake chain
Yoshihiko Ogata (The Institute of Statistical Mathematics)
In Japan, the aftershock activity has been forecasted1) since the 1995 Hanshin-Awaji Earthquake, but due to the 2016 Kumamoto earthquakes, numerical forecasts have been refrained. However, the case of the Kumamoto earthquakes is stochastically not unusual. Moreover, earthquakes of the same magnitude or larger than the mainshock are much more likely to occur within a few days of the mainshock than the rest of period. Therefore, it is desirable to statistically overcome the loss of aftershock data due to the decline in detection capability immediately after a large earthquake and start probability prediction immediately after that.
In addition, the ETAS model may be utilized for ex-post medium- and long-term forecastsalthough the ETAS model useful for more accurate forecasts2), but it is required to implement spatio-temporal forecasts in response to assumed scenarios based on seismological findings and the individuality of various seismic activities. For example, in California, a probabilistic simulation method based on a group of fault segmentation models (UCERF3-ETAS)3) has been proposed and studied. In this presentation, I would like to further discuss some characteristics4),5) of seismic activity before and after the Nankai Trough chain of earthquakes during the Showa period and look forward to the challenges of spatio-temporal forecasting that can pursue the probability of chain earthquakes in real time.
- 1) Earthquake Headquarters, Earthquake Research Committee (1998) Probability Evaluation Methodology for Forecasting, (in Japanese) https://www.jishin.go.jp/main/yoshin2/yoshin2.htm
- 2) Earthquake Headquarters, Seismological Commission of Japan (2001) Methodology for evaluating the long-term probability of earthquakes (in Japanese) https://www.jishin.go.jp/reports/research_report/choukihyoka_01b/
- 3) US Geological Survey (2022) UCERF3 ETAS, http://wgcep.org/UCERF3-ETAS.html
- 4) Ogata (2003) Seismicity quiescence and activation in western Japan associated with 1944 and 1946 great earthquakes near the Nankai Trough, Report of Coordinating Committee for Earthquake Prediction, August 2003, Vol 70 (7-3), pp. 378-383. http://cais.gsi.go.jp/YOCHIREN/report/kaihou70/07-03.pdf
- 5) Ogata, Y. (2004). Seismicity quiescence and activation in western Japan associated with the 1944 and 1946 great earthquakes near the Nankai trough, J. Geophys. Res., Vol.109, No.B4, B04305, doi:10.1029/2003JB002634.