Expedition 348 summary

Abstract

The Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) is a multidisciplinary investigation of fault mechanics and seismogenesis along subduction megathrusts and includes reflection and refraction seismic imaging, direct sampling by drilling, in situ measurements, and long-term monitoring in conjunction with laboratory and numerical modeling studies. The fundamental objectives of NanTroSEIZE are to characterize the nature of fault slip and strain accumulation, fault and wall rock composition, fault architecture, and state variables throughout an active plate boundary system. As part of the NanTroSEIZE program, operations during Integrated Ocean Drilling Program (IODP) Expedition 348 were planned to extend and case riser Hole C0002F, begun during IODP Expedition 326 in 2010 and continued during Expedition 338 in 2012, from 860 to 3600 meters below the seafloor (mbsf).Riser operations during Expedition 348 were carried out and deepened the hole to 3058 mbsf, a new maximum depth record in scientific ocean drilling. Operations included installation and cementing of 13 3 ⁄8 inch casing to 2008.9 mbsf and an 11¾ inch liner to 2922.5 mbsf, stabilizing the borehole for future deepening. Reaching this depth required two sidetracking operations from the original Hole C0002F, resulting in the designation of Holes C0002N and C0002P for the successively deeper sidetracks. During drilling, a suite of logging-while-drilling (LWD) and measurement-while-drilling (MWD), mud-gas, and cuttings data were collected over the interval from 2162.5 to 3058.5 mbsf in Hole C0002P, and a partial suite was collected in Hole C0002N. The interval from 2163 to 2218 mbsf was cored with the rotary core barrel (RCB). Planned future riser drilling operations will deepen the hole to penetrate the plate boundary fault at ~4600-5200 mbsf.Additionally, a test hole for a prototype slimhole small-diameter RCB (SD-RCB) coring system, Hole C0002M, was drilled in riserless mode near Hole C0002F. The hole was advanced to 475 mbsf, where four cores were collected to 512.5 mbsf.Overall, Expedition 348 sampled and logged a deep interval in Holes C0002N and C0002P within the inner accretionary wedge, from 856 to 3058.5 mbsf, including a never-before sampled zone in the lowermost ~1 km of drilling. Cores were collected over a 55.5 m interval from 2163 to 2218.5 mbsf. The sampled sedimentary rocks are composed of hemipelagic sediment and fine turbi-

The origin of strata within the inner accretionary prism of Nankai Trough: Evidence from clay mineral assemblages along the NanTroSEIZE transect

“…IODP Site C0002 is positioned near the seaward edge of the Kumano Basin (Figure ). A combination of riserless and riser drilling during IODP Expeditions 315, 338, and 348 extended boreholes through the forearc basin into intermediate depths of the inner accretionary prism, reaching a maximum depth of 3058 mbsf (Ashi et al, ; Strasser et al, ; Tobin et al, ). Analysis of 3‐D seismic data in the vicinity of Site C0002 provides clear evidence of thrust fault reactivation after the forearc basin formed (Boston, Moore, Jurado, & Sone, ).…”

“…Seismic reflection profile through IODP Site C0002 (from Tobin et al, ) with summary of lithofacies stratigraphy. The forearc‐basin facies is separated from the underlying accretionary prism by a prominent unconformity.…”

Data report: clay mineral assemblages in the upper Shikoku Basin, results from IODP Expedition 333, Sites C0011 and C0012

“…The Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) comprises several sampling expeditions that crossed the subduction system offshore southwest Japan Screaton et al, 2009;Tobin et al, 2009Tobin et al, , 2015Underwood et al, 2010;Strasser et al, 2014; see the "Expedition 333 summary" chapter [Expedition 333 Scientists, 2012a]). Integrated Ocean Drilling Program (IODP) Expeditions 322 and 333 concentrated on coring the inputs of sediment to the subduction zone (see Underwood et al, 2010; also see the "Expedition 333 summary" chapter [Expedition 333 Scientists, 2012a]).…”

Data report: permeability and microfabric of core samples from IODP Expedition 348, Hole C0002P, Nankai Trough accretionary prism

“…Site C0002 (Fig. F1) is located on the upper plate of the subduction zone above the seismogenic (presumably locked) portion of the plate boundary thrust system (see the "Expedition 348 summary" chapter [Tobin et al, 2015a]). The long-term goal of deeper drilling at this site is to cross the megasplay at seismogenic depths where coseismic slip occurred during the 1944 Tonankai earthquake (Ichinose et al, 2003).…”

“…Those coarser textures should increase values of permeability. Furthermore, the strata dip steeply over the cored interval, typically at angles >80° (see the "Expedition 348 summary" chapter [Tobin et al, 2015a]). Those orientations should alter the anisotropy of permeability (i.e., horizontal versus vertical) relative to a normally compacted sedimentary basin.…”