有人潜水調査船しんかい6500によって明らかになった釧路海底谷西壁の地質構造

摘要

Two Shinkai 6500, human occupied vehicle (HOV) dive surveys were performed on the sidewall in the Kushiro Submarine Canyon, off Tokachi, NW Pacific Ocean. These dives, 6K#1033 and 6K#1035, allowed observation of the geologic architecture of the Kuril trench. Samples from the canyon wall provide examples of deformation textures of fault-zone rocks and associated measured uniaxial compressive strengths of these rocks. The 6K#1033 and 6K#1035 dives surveyed in the middle part of the canyon. The dive area is divided into a highly deformed zone and non-deformed zone based on geological structures and stratal orientation. The highly deformed strata are cut and deformed by normal faults, thrusts, liquefaction and vein structures. The strata mostly strike NE-SW and dip south. The average value of the uniaxial compressive strengths in three specimens collected from highly deformed strata are 1.12-1.30 MPa. The horizontal strata unconformably overlie the highly deformed strata. At the base of the horizontal strata, a more than 1-m-thick conglomerate layer was observed. Average values of the uniaxial compressive strengths of two specimens collected during 6K#1032 dive (dive survey at upper horizontal layers of the canyon) were 0.46 MPa and 0.58 MPa. Given these observations, I suggest that cessation of deformation coincided with deposition of the conglomerate layer.