9:45 AM - 10:00 AM
[J08-2-06] Investigation of seismicity and subsurface structure around northern Tohoku using seismic data recorded by AS-net
From 2013 to 2014, we have installed a permanent local high-sensitivity seismic observation network, AS-net, at northern Tohoku and southwestern Hokkaido, Japan, for the purpose of monitoring earthquake activity and investigation of subsurface structure. AS-net covers the area where the other seismic stations are relatively sparse, and enhances the earthquake detection capability and provides dense continuous seismic data. The region is located on the Japan island arc containing fore-arc, back-arc showing relatively higher seismicity in Japan. In this presentation, we report the seismic activity and subsurface structure around northern Tohoku containing Aomori prefecture and southwestern Hokkaido investigated using data derived by AS-net and other stations.
We are making an original local earthquake catalogue for northern Tohoku from 2014 using data from 134 stations including 36 stations of AS-net. 11191 events were detected automatically using data from January 2014 to June 2016. By manual check of these events, 5961 earthquakes were determined. 4535 earthquakes were occurred in the crust (H <50 km), and the other were occurred at the upper boundary and the inside of Pacific plate. Some low-frequency events also occurred at some volcanic and non-volcanic regions (H <40 km). Above these low-frequency events, shallow normal earthquakes also occur actively. For crustal earthquakes (H <50 km), we could detect 2.5 times as many earthquakes as JMA hypocenter catalogue (1752 events). The site corrections for P and S arrival estimated using the difference between manual pick and theoretical travel time are considered in this hypocentral location. The site correction values differ depending on subregions reflecting their local site conditions. We also conduct seismic tomography using manual phase pick values for hypocentral location. We show the relationship between hypocentral distribution and the subsurface structure shown by the seismic tomography.
We are making an original local earthquake catalogue for northern Tohoku from 2014 using data from 134 stations including 36 stations of AS-net. 11191 events were detected automatically using data from January 2014 to June 2016. By manual check of these events, 5961 earthquakes were determined. 4535 earthquakes were occurred in the crust (H <50 km), and the other were occurred at the upper boundary and the inside of Pacific plate. Some low-frequency events also occurred at some volcanic and non-volcanic regions (H <40 km). Above these low-frequency events, shallow normal earthquakes also occur actively. For crustal earthquakes (H <50 km), we could detect 2.5 times as many earthquakes as JMA hypocenter catalogue (1752 events). The site corrections for P and S arrival estimated using the difference between manual pick and theoretical travel time are considered in this hypocentral location. The site correction values differ depending on subregions reflecting their local site conditions. We also conduct seismic tomography using manual phase pick values for hypocentral location. We show the relationship between hypocentral distribution and the subsurface structure shown by the seismic tomography.