Physical and Mechanical Properties of the Kumano Forearc Basin Sediments at Iodp Site C0025

Knowledge of the mechanical properties of Kumano forearc basin sediments is crucial for building accurate geological models for various marine projects that require drilling. We used small samples, which simulated drilling cuttings, collected from Kumano forearc basin sediments retrieved from International Ocean Discovery Program Site C0025 to determine the depth profiles of P- and S-wave velocities, porosity, and rock strength. In our results, the S-wave velocity and unconfined compressive strength gradually increased with increasing depth, whereas the P-wave velocity and porosity were almost constant in a depth range of about 400–572 mbsf. In addition, the permeability of the sediments decreased with increasing depth. As a result, the mechanical properties of less consolidated sediments were successfully obtained from small samples (<2 cm in size) that simulated drilling cuttings. We also confirmed the estimated rock strengths from indentation tests on the small samples are consistent with the measured rock strength from triaxial compression tests on cores. The smooth depth trends of these mechanical properties are possibly caused by evenly disseminated gas hydrate.