Study of the thermal structure of the seismogenic zone along the Nankai margin through heat flow measurements in shallow sea areas

1.我们使用弹出式仪器对沉积物温度剖面和底层水温进行了长期监测。在沿着的17个测站获得了5 ~ 17个月的连续记录。从沉积物温度记录中扣除底层水温变化的影响，我们可以得到六个水深相对较浅的站的热流值。我们还表明，它是可能的，以确定在浅海热流通过分析沉积物温度剖面测量与普通深海探头结合长期的底层水温记录。将该方法应用于三个台站的观测数据，成功地确定了地表热流.我们根据长期的底层水温记录，评估了使用普通探头可以测量热流的最小水深以及使用弹出式仪器确定热流所需的监测时间长度。底层水温的变化也与物理海洋学数据进行了比较。温度变化的周期性可能与黑潮的弯曲有关.还使用普通探测器在深海区域进行了热流测量。综合上述浅海区的观测结果和现有的观测资料，我们可以建立起纪伊半岛东南海域（熊野近海）的南海海槽热流剖面.在熊野外和四国东部外计算了南海俯冲带的温度结构，考虑到沉积作用对传入的海洋板块和流体和沉积物流动的增生棱柱。我们估计沿着板块边界的摩擦加热（剪切应力）通过比较计算的表面热流与观测数据。

1. We conducted long-term monitoring of temperature profiles in sediments and bottom water temperature using pop-up type instruments. Continuous records for 5 to 17 months were obtained at 17 stations along the Nankai margin.2. Reducing the effect of bottom water temperature variation from the sediment temperature records, we could obtain heat flow values at six stations with relatively shallow water depths. We also showed that it is possible to determine heat flow in shallow sea by analyzing sediment temperature profiles measured with ordinary deep-sea probes in combination with long-term bottom water temperature records. This new method was applied to the data at three stations and heat flow was successfully determined.3. We evaluated the minimum water depth at which heat flow can be measured with ordinary probes and the length of monitoring time with pop-up type instruments necessary for heat flow determination based on long-term bottom water temperature records. Variations in bottom water temperature were also compared with physical oceanography data. The periodicity in the temperature variations might be related to meandering of the surface current (Kuroshio).4. Heat flow measurements were also made in deep sea areas using ordinary probes. Combining the obtained data with the results in shallow sea areas mentioned above and the existing data, we could construct a heat flow profile across the Nankai Trough in the area southeast of the Ki-i peninsula (off-Kumano).5. The temperature structure of the Nankai subduction zone was calculated in the off-Kumano area and in the areas off eastern Shikoku, taking account of effects of sedimentation on the incoming oceanic plate and fluid and sediment flows in the accretionary prism. We estimated the frictional heating (shear stress) along the plate boundary by comparing the calculated surface heat flow with the observed data.