Analysis of Ignitions Following 2011 Tohoku Earthquake Using Kawasumi Model

Abstract

Ignitions following the Tohoku earthquake (2011) can be divided either into earthquake-generated ignitions or tsunami-generated ignitions. This study analyzed the behavior of the earthquake-generated ignitions. Ignition records of 698 municipalities of eastern Japan was collected by a questionnaire survey and found that 191 ignitions were either directly or indirectly caused by seismic motion. These records of earthquakegenerated ignition were analyzed using the statistical model proposed by Kawasumi (Kawasumi model). Kawasumi model is a simple one-parameter model which formulates the relationship between the ignition probability p and the scale of seismic intensity θ. Seismic indices θ used in this analysis were (a) collapse ratio of houses, (b) JMA (Japan Meteorological Association) seismic intensity, (c) PGA (peak ground acceleration), (d) PGV (peak ground velocity), (e) PGD (peak ground displacement), (f) acceleration response and (g) SI (Spectral Intensity). Obtained adjusted determination coefficients were higher than 0.7 for most of the seismic indices θ except for (a) collapse ratio of houses and (e) PGD. After normalization with regard to time and season of its occurrence, the results were further compared with that of various earthquakes (1927-1968), and the Kobe earthquake (1995). Ignition probability p of the Tohoku earthquake (2011) was substantially lower than that of the various earthquakes (1927-1968). On the other hand, the difference of ignition probability p between the Tohoku earthquake (2011) and Kobe earthquake (1995) was relatively small.