Conditional Probabilities of Occurrence of Moderate Earthquakes in Indian Region

Abstract eng:
A problem of increasing concern in India is the likelihood of occurrence of the next large earthquake in the areas where the last occurrence has crossed the return periods. The seismic hazard estimated based on the classical methodologies available as such do not consider the timing of the last occurrence of the damaging earthquake in the area while giving the probabilities of occurrence of the next such event. The average return period or recurrence interval as derived in the seismic hazard assessments does not in and of itself supply sufficient information of determining the probability of occurrence. It is also necessary to know the frequency distribution of recurrence intervals of a given magnitude or magnitude range. The conditional probabilities of occurrence of earthquakes have been estimated for the seismogenic sources in Indian region using the Weibull distribution. The estimations have been carried out by dividing the Indian subcontinent into 24 seismogenic sources. The cumulative probabilities estimation reveals that the zone Z2 and Z9 have the highest probabilities of occurrence of earthquake of maximum observed magnitude in the region. The return periods for these zones were estimated as 9 and 18 years while the last occurrence has been in the years 1940 and 1958, respectively. Ten zones namely, Z2, Z6, Z7, Z8, Z9, Z10, Z12, Z14, Z23 and Z24 out of the 24 zones were found to be having relatively higher conditional probabilities of occurrence of earthquake with maximum observed magnitude in the vicinity of 2005. Comparison of conditional probabilities with the classical approach emphasize that most of the part of the Indian continent is earthquake prone and it is necessary to consider the last occurrence of earthquake while estimating the seismic hazard for any region.

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