[S-SS26_30PM1] Crustal Structure

[SSS26-01] Relationship between half-graben and high-velocities area at depths of 10 km 7

*Yukio OISHI¹ (1.Atelier Science)

There are four oval shaped high velocities areas in Kanto Area .Two of them are in the southern part of Ibaraki prefecture. (after Matsubara Makoto 2005) These two high velocities areas in Ibaraki prefecture gets larger, the deeper you see. At the depths of about 30km, this huge high velocities mass ,whose shape is donut, almost covers the southern part of Ibaraki prefecture and reaches at the depths of about 50km.The western half of this huge high velocities area is on The Fourth Plate under Kanto; a part of Philippine Sea Plate(Toda Shinji 2005) at the depths of about 50km.The eastern half of huge high velocities mass rides on the low velocities and low Poisson's ratio area, that is under beneath Lake Kasumigaura and the Southern of Lake Kasumigaura.( after Matsubara Makoto 2008)This low velocities and low Poisson's ratio area faces subducting Pacific Plate at the depths of about 70 km. Speaking of the low velocities and low Poisson's ratio area , the similar area exists in the asperity of M9 in 2011 off the Pacific Coast of Tohoku Earthquake; the upper part of the Pacific plate and also exists in Unzen in Nagasaki prefecture from the ground to the depths of about 30km.I pointed out the possibility that the flexibility of the existence of the felsic rock or magma developed adherence of asperity of M9. ( Ohishi Yukio 2013)From the above it seems to be necessary to examine the possibility of the major earthquake outbreak underneath Lake Kasumigaura and the Southern Lake Kasumigaura at the depths of about from 50km to 70km. There is another view that this low velocities area is not low Poisson's area but high Poisson's area (Nakajima Junichi 2008).I want to wait for solution.