Spatial Features of Intermediate-Depth Seismicity in the Pacific Plate Beneath Northeastern Japan and Their Implications to the Formation of the Volcanic Front

Details Spatial Features of Intermediate-Depth Seismicity in the Pacific Plate Beneath Northeastern Japan and Their Implications to the Formation of the Volcanic Front Spatial Features of Intermediate-Depth Seismicity in the Pacific Plate Beneath Northeastern Japan and Their Implications to the Formation of the Volcanic Front

Dec 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agufm.s51a0591y&link_type=abstract

American Geophysical Union, Fall Meeting 2001, abstract #S51A-0591

Other

7230 Seismicity And Seismotectonics, 7280 Volcano Seismology (8419), 8450 Planetary Volcanism (5480)

Scientific paper

Having investigated spatial variation of seismicity in the Pacific plate subducted under northeastern Japan, we found that density of earthquakes in the upper seismic plane in the slab decreases remarkably beneath the Volcanic Front and on its deeper side. The spatial change in the seismicity is so sharp that we can easily mark the point where the seismicity begins to decrease for each slit zone taken in the east-west direction or perpendicular to the Volcanic Front. The depth of the upper seismic plane at the critical point is about 100km in the Tohoku district. On the other hand the depth of the points in the Kanto district is apparently deeper (130-140km), and it is seen that the upper seismic plane coalesces to the lower seismic plane at the depth of 120-130km in Hokkaido. A line connecting the above-mentioned points delineates eastern boundary of the distribution of active volcanoes and it runs almost parallel to the Volcanic Font. The line, however, is located somewhat to the east of the Volcanic Front in the Kanto district. We think this discrepancy is caused by the subduction of the Philippine Sea plate over the Pacific plate in that region. Another notable fact is that the seismic activity in the upper plane shows high b-value just beneath the Volcanic Front. There are many documents reporting high b-value around magma bodies (Wiemer et al., 1997; Wyss et al., 2001). We consider that the above features of the seismicity in the upper plane, i.e., conspicuous decrease of the density of earthquakes and high b-value beneath the Volcanic Front, indicate that physicochemical processes causally related to magma genesis in subduction zones are progressing there.

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