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

<jats:title>Abstract</jats:title><jats:p>Laboratory measurements for compressional and shear wave velocities (<jats:styled-content style="fixed-case">V</jats:styled-content>p and <jats:styled-content style="fixed-case">V</jats:styled-content>s, respectively) and porosity were conducted with core samples from the <jats:styled-content style="fixed-case">N</jats:styled-content>obeoka <jats:styled-content style="fixed-case">T</jats:styled-content>hrust <jats:styled-content style="fixed-case">D</jats:styled-content>rilling <jats:styled-content style="fixed-case">P</jats:styled-content>roject (<jats:styled-content style="fixed-case">NOBELL</jats:styled-content>) 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 <jats:styled-content style="fixed-case">V</jats:styled-content>p, <jats:styled-content style="fixed-case">V</jats:styled-content>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 <jats:styled-content style="fixed-case">V</jats:styled-content>p and <jats:styled-content style="fixed-case">V</jats:styled-content>s and lower porosity than those measured by the previous studies that adopted the wire‐line logging methods. The variations in <jats:styled-content style="fixed-case">V</jats:styled-content>p, <jats:styled-content style="fixed-case">V</jats:styled-content>s, and porosity are controlled by deformation structure and are greater for phyllite and foliated cataclasite than for non‐foliated cataclasite.</jats:p>