Moho depth variation in the central part of northeastern Japan estimated from reflected and converted waves

We detected reflected P- and S-waves at the Moho in seismograms of shallow crustal earthquakes in the central part of northeastern (NE) Japan. P-to-S and S-to-P mode-converted waves at the Moho are also detected in seismograms of intermediate-depth earthquakes in the subducted Pacific slab. The depth distribution of the Moho in the central part of NE Japan is estimated by using travel time differences between these later phases and the first P and S arrivals. We collected travel time data of 496 reflected waves from 67 shallow earthquakes and 200 converted waves from 65 intermediate-depth earthquakes. The depth to the Moho estimated is deep beneath the land and becomes shallower toward the eastern and western coastlines. The Motto depth is about 34 km in the middle of the land area, about 30 kin under the coastline of the Japan Sea and 27-29 km under the coastline of the Pacific Ocean. (C) 2002 Elsevier Science B.V. All rights reserved.