Shear wave polarization anisotropy in the upper mantle beneath Honshu, Japan

摘要: Shear wave polarization anisotropy in the wedge portion of upper mantle between a subducting plate and earth's surface is investigated using three-component seismograms intermediate depth deep earthquakes recorded at 14 local stations Honshu, Japan. Eighty nine high-quality were selected from period 3 years. The data used this study are restricted such that incidence angles smaller than critical angle 30° to order avoid phase shifts shear train. To find directions maximum minimum velocities split waves, where waves resolved into two phases with time separation, each set horizontal component rotated plane. thus obtained again recombined after correction anisotropy, anisotropy-corrected particle motion compared focal mechanism for cross-check observed anisotropy. Directions axes plotted on azimuthincidence stereograms station. cross sections seismic ray paths show (1) anisotropic material distributed location earthquake sources receiving stations, (2) region separated parts: one north present area velocity trending 0° (north anisotropy) other south it 90° 120° (south anisotropy). delays along vertical about l s both regions. extent 50 km depths 150 km. perhaps prevalent west Honshu. However, not well constrained because insufficient coverage angles. If we assume be 100 km, contrast would 4%. adopt crack alignment model, cracks inferred vertically south. an olivine crystals aligned axis slip direction plane normal b being horizontal.