Study on early aftershock sequences: Simultaneous estimation of hypocenter and focal mechanism using seismogram amplitude

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The purpose of this study is to clarify the characteristics of early aftershock sequences by developing a method to estimate earthquake hypocenter using waveforms. For the 2011 off the Pacific Coast of Tohoku Earthquake, we determined hypocenters by an ordinary method and found that the aftershock area expanded with proportional to the logarithm of lapse time from the mainshock. The newly developed method uses correlation of waveforms and time difference between the template and continuous envelopes to estimate hypocenter. We applied the method to the aftershock sequence of the Tohoku Earthquake and found some problems to determine enough number of events. Though we need to improve the method, it is expected to be useful, for example, to know the geofluid distribution in the crust.