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

本研究的目的是通过发展一种利用波形估计震源的方法来阐明早期余震序列的特征。对于2011年东北太平洋沿岸地震，我们用普通方法确定了震源，发现余震面积与主震经过时间的对数成正比地扩大。该方法利用波形的相关性和模板包络与连续包络的时差来估计震源。我们将该方法应用于东北地震的余震序列，发现了一些问题，以确定足够的事件数。虽然该方法还有待改进，但它在了解地壳流体分布等方面仍有一定的应用价值。

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.