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[SCG57-P01] Thermal structure and evolution near the toe of Muroto accretionary prism inferred from seafloor/borehole data
Keywords:heat flow, IODP, slow earthquake
Understanding the "field" (temperature, pressure, stress, etc.) on and around the subduction-zone megathrust faults not only contributes to understanding the nature of the ingerseismic locking at the fault, but is also important for understanding the mechanisms of slow earthquakes and geodetic deformation (including slow slip) that occur around the locked zone. For the estimation of the geothermal field, the heat flux, both measured at the seafloor and estimated from the BSR depth, are mainly used. Spinelli and Wang (2008) reported a rapid decrease in heat flow toward land on the landward side of the trough axis (accretionary prism) and a high heat flow exceeding 200 mW/m^2 at the trough floor (e.g., Yamano et al., 2003). Spinelli and Wang (2008) argued that heat mining due to hydrothermal circulation causes low heat flow on the landward side and high heat flow on the seaward side (trough floor) around the deformation front (DF).
In the Nankai Trough accretionary complex off Cape Muroto, in-situ temperature measurements have been carried out up to 300 m below the seafloor by the ODP/IODP (Deep Sea Drilling Program and International Ocean Drilling Program), and three borehole stations have been established. The results of the ACORK and surface heat flow measurements show that near the Muroto DF, heat flow is high (>180 mW/m^2) on the seaward side (ODP-1174, 1173) of the first frontal fault (FT), but low near the first FT (IODP-C 0023) and landward of the first FT (ODP-808) (130-140 mW/m^2). On the other hand, localized high heat fluxes are observed at the outlet of the first and second FTs (Kawada et al., 2014), suggesting the fluid upwelling along the FTs. These results suggest that the heat flow transition pointed out in previous studies is occurring near the first FT and that pore water in the oceanic crust may be flowing out through the FT.
In the Muroto area, three boreholes (808, C0023, 1173) continue to monitor temperature and water pressure, or are being prepared to do so, and are likely to detect evidence of fluid movement and upwelling related to slow earthquakes and slow slip activities that frequently occur shallower than the sticking zone.
In the Nankai Trough accretionary complex off Cape Muroto, in-situ temperature measurements have been carried out up to 300 m below the seafloor by the ODP/IODP (Deep Sea Drilling Program and International Ocean Drilling Program), and three borehole stations have been established. The results of the ACORK and surface heat flow measurements show that near the Muroto DF, heat flow is high (>180 mW/m^2) on the seaward side (ODP-1174, 1173) of the first frontal fault (FT), but low near the first FT (IODP-C 0023) and landward of the first FT (ODP-808) (130-140 mW/m^2). On the other hand, localized high heat fluxes are observed at the outlet of the first and second FTs (Kawada et al., 2014), suggesting the fluid upwelling along the FTs. These results suggest that the heat flow transition pointed out in previous studies is occurring near the first FT and that pore water in the oceanic crust may be flowing out through the FT.
In the Muroto area, three boreholes (808, C0023, 1173) continue to monitor temperature and water pressure, or are being prepared to do so, and are likely to detect evidence of fluid movement and upwelling related to slow earthquakes and slow slip activities that frequently occur shallower than the sticking zone.