On the connection of fractures with clays and fluids in the accretionary prism of the Nankai Trough at Site C0002, NanTroSEIZE IODP Expedition 338/348. Borehole images and log interpretation results

International Ocean Discovery Program IODP has extensively used the D/V Chikyu to drill the Kumano portion of the Nankai Trough. (IODP) Expeditions 338 and 348 of the NanTroSEIZE project drilled deep into the inner accretionary prism south of the Kii Peninsula collecting a suite of LWD data, including natural gamma ray, electrical resistivity logs and borehole images, suitable to characterize structures (fractures and faults) inside the accretionary prism. Both expeditions drilled into the accretionary prism at Site C0002: Hole C0002F (Expedition 338) was drilled down to 2004.5 mbsf, Hole C0002P (Expedition 348) reached a depth of 3058.8 mbsf. Structural interpretation and analysis of logging-while-drilling data in the deep inner prism revealed intense deformation of a generally homogenous bedding that dips steeply and are intersected by faults and fractures. The interpretation of the images of both Hole C0002F and Hole C0002P reveals distinct areas of intense fracturing and faulting within a very clay-dominated lithology. Faults are undobutedly interpreted on C0002P images. The relationship between fractures, faults and the changes in clay mineralogy from cutting sample analyses is analyzed to characterize potential connection between these features in the accretionary prism ; Peer Reviewed