3 dimensinal structure and history of seismic Janlt of 1923 type Kanto Earthqnakc

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Sagami Bay is quite unique in terms of geo-tectonic setting, becasuse it locates on the plate boundary between the North-American and the Philippine Sea plates. In the Sagami Bay, the North-American plate is charcterized by non-volcanic terrane with alignment of several knolls and banks, parallel to the boundary. The morphology seems to represent compressional tectonis feature rather than tentioaal one as was proposed by Nakamura (1986). On the other hand, the Philippine Sea plate is characterized by volcanic terrane and no distinct structure characterized by compressional deformatiom is identified on the Philippine Sea plate except Maizuru Knoll. Some monogenic volcanoes are seen along the Izu Peninsula in south-western part of the bay.North-American Plate ;Revease faults and folding in relation to plate boundary are identified on the MCS (multichannel seismic) profiles. Deep tow chirp sonar profile from the Tokyo Canyon crossing plate boundary, also, reveals flexture of surface sedim … More ents, suggesting that the deformation is quite active. Because the sedimentation rate in the Tokyo Canyon is estimated to be very high. Deep crustal structure obtained by OBS survey shows eastward dipping layr west of the plate boundary and crustal discontinuity at the boubary. We interprete the discontinuity to be formed by reverse fault. Moreover Izanagi sea floore image shows well developed gully structure, particularly on the southwestern margin of knolls and bank in non-vocanic terrane. We interprete that hydroflucturing is assumed to occur on the southwestern margin of the Eurasian plate due to high pore pressure, induced by underthrusting of the Philippine Sea plate below the North-American plate. Consequently, we can conclude that the plate boundary between the North-Americn and Philippine Sea plates is convergent margin.Philippine Sea palte ;The MCS profile runnig across the Manazuru knoll shows thrust faults at the southern margin of the Manazuru knoll dipping to the north. OBS data support the interpretation of MCS profile. Additional major fault is identified with a trend of NNW-SSE along the Izu Peninsula based on lineament obtained by Izanagi data and linear distribution of clam colonies found out by diving observation. sigma Hmax determined by spatial distribution of dykes is NNW,suggesting the occurrence of left lateral strike-slip fault with a trend of NNW-SSE.We interprete Magmas of monogenic volcanoes is assumed to intrude along the fault, because the monogenic volcanoes distribute close to the fault Less