NanTroCORK: Development of hydrologic long-term CORK observatories in the seismogenic Nankai Trough subduction zone, Japan

IODP已经启动了复杂的钻探项目“NantroSEIZE”(南开海槽地震孕育区实验)，这是一个多阶段的努力，将7个地点的横断面钻探到日本近海的俯冲巨型金字塔。NANROSEIZE的一个基本目标是建立一个分布的长期观测网，覆盖从传入板块向下延伸到孕震带上倾极限的区域。我们在这里建议在两个钻探地点安装，这两个地点由俯冲系统的前弧前部的高应变和快速脱水控制。在这些地点，将在沉积楔形和俯冲序列的沉积物中监测孔压(作为应变的替代)和温度，以及在相应的进一步向上倾斜中进行监测。选定的地点对监测特别重要，因为它们位于俯冲的欧亚板块(新台币1-03)和下行的菲律宾海板块(新台币1-07)。在前一个位置，棱柱体脚趾处的正面推力将被穿透，一旦第三阶段钻井与那里的板块边界相交，安装的仪器最终将能够与类似的向下倾斜的仪器“沟通”。在后一个地点，整个俯冲输入将在原地表征，这是特别重要的，因为下部的砂岩是渗透性的，并被发现充满了深层流体。仪器的开发将与将于2008年春季安装的美国软木塞并行进行，这一工作已经在进行中。

IODP has started the complex drilling project "NanTroSEIZE" (Nankai Trough Seismogenic Zone Experiment), a multi-stage effort to drill a transect of 7 sites into the the subduction megathrust off Japan. One fundamental goal of NanTroSEIZE is the establishment of a distributed long-term observatory network spanning the incoming plate down to up-dip limit of the seismogenic zone. We here propose installations at two drillsites which are governed by high strains and rapid dewatering in the frontal forearc of the subduction system. At these sites, pore pressure (as a proxy for strain) and temperature will be monitored in sediments of the accretionary wedge and underthrust succession as well as in their equivalent further up-dip. The selected sites are especially critical for monitoring because of their location at the overriding Eurasian Plate (NT 1-03) and the downgoing Phillipine Sea Plate (NT 1-07). In the former location, the frontal thrust at the prism toe will be penetrated, and the installed instruments will be able to eventually "communicate" with similar ones down-dip once Stage 3 drilling intersects the plate boundary there. At the latter site, the entire subduction input will be characterized in situ, which is particularly vital since sands in the lower portion are permeable and have been found charged with deep-seated fluids. Instrument development will be carried out in parallel with an US CORK to be installed in spring 2008, which is already underway.