Determination of principal stress orientations from wireline logging caliper data and borehole images in deep drilling

摘要

A deep borehole was drilled at site C0009 in the center of the Kumano forearc basin in the southwest Japan Nankai subduction zone, as a part of the scientific ocean drilling project called NanTroSEIZE. Principal horizontal stress orientations were determined from analyses of borehole breakouts by using wireline logging formation microresistivity images and caliper data. The orientation of maximum horizontal stress at C0009 is approximately parallel to the convergence vector between the Philippine Sea plate and Japan, showing a slight difference with the stress orientation which is perpendicular to the plate boundary at previous drilling sites C0001, C0004 and C0006 but orthogonal to the stress orientation at site C0002, which is also in the Kumano forearc basin. These data show that horizontal stress orientations are not uniform in the forearc basin within the surveyed depth range and suggest that oblique plate motion is being partitioned into strike-slip and thrusting.