Acoustic properties of deformed rocks in the N obeoka thrust, in the S himanto B elt, K yushu, S outhwest J apan

Abstract

Laboratory measurements for compressional and shear wave velocities ( V p and V s, respectively) and porosity were conducted with core samples from the N obeoka T hrust D rilling P roject ( NOBELL ) under controlled effective pressure (5–65 MPa at 5 MPa intervals) and wet conditions. Samples were classified according to deformation texture as phyllite, foliated cataclasite, or non‐foliated cataclasite. Measured values of V p, V s, and porosity are within a range of 5.17–5.57 km/s, 2.60–2.71 km/s, and 2.75–3.10 %, respectively, for phyllite; 4.89–5.23 km/s, 2.46–2.57 km/s, and 3.58–4.53 %, respectively, for foliated cataclasite; and 4.90–5.32 km/s, 2.51–2.63 km/s, and 3.79–4.60 %, respectively, for non‐foliated cataclasite, which are all consistent with the previous laboratory experiments conducted with outcrop samples under dry conditions. However, our results also indicate higher V p and V s and lower porosity than those measured by the previous studies that adopted the wire‐line logging methods. The variations in V p, V s, and porosity are controlled by deformation structure and are greater for phyllite and foliated cataclasite than for non‐foliated cataclasite.

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