Abstract
The Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) is a major drilling project designed to investigate fault mechanics and the seismogenic behavior of subduction zone plate boundaries. Expedition 319 is the first riser drilling operation within scientific ocean drilling. Operations included riser drilling at Site C0009 in the forearc basin above the plate boundary fault, non-riser drilling at Site C0010 across the shallow part of the megasplay fault system &ndash; which may slip during plate boundary earthquakes &ndash; and initial drilling at Site C0011 (incoming oceanic plate) for Expedition 322. At Site C0009, new methods were tested, including analysis of drill mud cuttings and gas, and <i>in situ</i> measurements of stress, pore pressure, and permeability. These results, in conjunction with earlier drilling, will provide (a) the history of forearc basin development (including links to growth of the megasplay fault system and modern prism), (b) the first <i>in situ</i> hydrological measurements of the plate boundary hanging wall, and (c) integration of <i>in situ</i> stress measurements (orientation and magnitude) across the forearc and with depth. A vertical seismic profile (VSP) experiment provides improved constraints on the deeper structure of the subduction zone. At Site C0010, logging-while-drilling measurements indicate significant changes in fault zone and hanging wall properties over short (< 5 km) along-strike distances, suggesting different burial and/or uplift history. The first borehole observatory instruments were installed at Site C0010 to monitor pressure and temperature within the megasplay fault zone, and methods of deployment of more complex observatory instruments were tested for future operations. <br><br> doi:<a href="http://dx.doi.org/10.2204/iodp.sd.10.01.2010" target="_blank">10.2204/iodp.sd.10.01.2010</a>
Highlights
The Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) is a major drilling project designed to investigate fault mechanics and the seismogenic behavior of subduction zone plate boundaries
Wireline log Formation MicroImager (FMI) resistivity images and caliper data were used to identify the orientation of borehole enlargement, indicating the minimum horizontal stress orientation (“borehole breakouts”)
Minimum horizontal stress consistently trends NE-SW downhole (~700–1600 mbsf); the maximum horizontal stress trends NW-SE (Fig. 6). This is similar to that observed in other boreholes across the accretionary prism and megasplay fault (TDs of ~400-1000 mbsf for NanTroSEIZE Stage 1 boreholes; see Kinoshita et al, 2009b), and is perpendicular to the margin and roughly parallel to the plate convergence direction (Fig. 6)
Summary
Introduction tested, including analysis of drill mud cuttings and gas, and in situ measurements of stress, pore pressure, and permeability. These results, in conjunction with earlier drilling, will provide a) the history of forearc basin development (including links to growth of the megasplay fault system and modern prism), b) the first in situ hydrological measurements of the plate boundary hanging wall, and c) integration of in situ stress measurements (orientation and magnitude). To this end, the Integrated Ocean Drilling Program (IODP) Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) project (Tobin and Kinoshita, 2006) has been
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