釧路沖の中規模繰り返し地震活動

Abstract

We identified 10 moderate sized repeating earthquakes from 1954 to 2010 off Kushiro region, eastern Hokkaido, Japan, by careful visual and quantitative inspections of waveform data. Relocated hypocenters calculated by reconfirmed arrival time data indicated that these earthquakes occurred at the same location on the interface between the subducting Pacific plate and the overriding plate. Reanalysis of focal mechanisms of recent three events showed approximately the same solution. These facts strongly suggested recurrent rupturing of an asperity. Average magnitude and average recurrence interval were M4.9 and 6.2±0.88 years, respectively. Estimated average slip rate was 6.5cm/year, which is equivalent to an interplate coupling ratio of 78-86%. The next earthquake is expected to occur in a period between May 2015 and July 2017 with a 70% probability based on the small sampling theory with a lognormal distribution model. Recurrent interval tended to shorten when large earthquakes occurred in the surrounding region. This might suggest recurrence interval is probably affected by the stress disturbance due to coseismic and postseismic slip on the plate interface.