Aftershock Hazard Magnitude, Time, and Location Probability Forecasting

  • Author(s): Kuei-Pao Chen, Yi-Ben Tsai, Wen-Yen Chang, and Ming-Wey Huang
  • DOI: 10.3319/TAO.2013.08.20.01(T)
  • Keywords: Branching aftershock sequence, Forecasting, Magnitude difference, Omori’s law

This study combines branching aftershock sequence (BASS) and modified Omori¡¦s law to develop a predictive model for forecasting the magnitude, time, and location of aftershocks of magnitude Mw ≥ 5.00 in large earthquakes. The developed model is presented and applied to the 17:47 20 September 1999 Mw 7.45 Chi-Chi earthquake Taiwan, 09:32 5 November 2009 (UTC) Nantou Mw 6.19, 00:18 4 March 2010 (UTC) Jiashian Mw 6.49 earthquake sequences, Taiwan, and 05:46 11 March 2011 (UTC) Tohoku Mw 9.00 earthquake, Japan. The estimated peak ground acceleration (PGA) results are remarkably similar to calculations from the recorded magnitudes in both trend and level. This study proposes an empirical equation to improve the aftershock occurrence forecast time. The forecast time results were greatly improved. The magnitude of aftershocks generally decreases with time. It was found that the aftershock forecast probability of Mw ≥ 5.00 is high in the first six days after the main shock. The results will be of interest to seismic mitigation specialists.

Spatial and temporal seismicity parameters to the aftershock sequence investigation into the 17:47 20 September 1999 (UTC) Mw 7.45 Chi-Chi earthquake, Taiwan found that immediately after the earthquake the area closest to the epicenter had a lower b value. This pattern suggests that at the time of the Chi-Chi earthquake, the area closest to the epicenter remained prone to large magnitude aftershocks and strong shaking. With time, however, the b value increased, indicating a reduced likelihood for large magnitude aftershocks.

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