A value of 6.6 km/sec is obtained for the velocity in the basaltic layer from an analysis through arrival time data observed by a seismic array network of Kitakami, located in Iwate Prefecture. It is found that the array network observes first Pg arrivals from some events occurring about 80 km south from the array. It is shown that these observations are more consistent with a velocity model of thick granitic layer at the eastern part of the Tohoku District, which has been derived from local earthquake data, than with a velocity model of thin granitic layer derived from explosion seismic observations. We determine lateral variations of the Moho depth beneath the Tohoku District by the use of arrival times of the P and S waves from local earthquakes. The Moho is deep beneath the central part of the Tohoku District and becomes shallower toward both the eastern and western coast lines. The Moho is located at depths ranging from 28 to 34 km. The position of the Moho at the central part is deeper by about 5 km than that of the previous models.
ASJC Scopus subject areas
- Earth and Planetary Sciences(all)