16:30 〜 19:00
[T1-P-1] Physical properties of the Kumano forearc basin at Site C0025, IODP Expedition 358
キーワード：IODP、南海トラフ、熊野前弧海盆
The International Ocean Discovery Program (IODP) Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) Expedition 358 penetrated the Kumano forearc basin at Site C0025 to understand the evolution of the accretionary prism and Kumano forearc basin in the Nankai Trough (Tobin et al., 2020, IODP Proceedings). Site C0025, located at ~ 50 – 55 km landward from the trench, has been drilled and obtained core samples from 400 – 573 mbsf. In this study, we conduct elastic wave velocity (Vp) and porosity measurements and indentation tests on cubic samples and estimate the anisotropy of the samples. Vp at 453 – 572 mbsf falls in the range of 1.7 to 2.0 km/s. Vp along horizontal directions show similar values with shipboard data, while Vp along vertical direction tends to be slightly higher than shipboard data (Tobin et al., 2020, IODP Proceedings). The vertical anisotropy of Vp is between -0.3 and 2.3%, which is similar with shipboard data. Porosity of our samples ranges between 42 – 49%, which is also consistent with the results of shipboard measurements (Tobin et al., 2020, IODP Proceedings). The unconfined compressive strength (C0) along horizontal direction, which can be obtained by indentation tests (e.g., Kitamura and Hirose, 2017, JSG), generally increases with depth from 0.6 MPa at 433 mbsf to 2.4 MPa at 454 mbsf. After C0 value decreases to 1.4 MPa at 467 mbsf, it gradually increases with depth to 3.0 MPa at 573 mbsf. C0 for vertical direction indicates the similar trend. The vertical anisotropy of C0 decreases with depth from 9.2% at 467 mbsf to -8.4% at 573 mbsf. In addition, we perform permeability measurements on core sample under in-situ pressure condition. The permeability of the sediment collected at 573 mbsf is on the order of 10-18 m2. In the poster, we will discuss the Vp-porosity, Vp-C0 and permeability-porosity relationships in the Kumano forearc basin.