11:15 AM - 11:30 AM
[SCG53-03] Heat flow anomalies observed on the seafloor in the vicinity of faults: indication of fluid flow
Keywords:heat flow anomaly, fluid flow, fault, heat transport, long-term monitoring
Accretionary prism developed landward of the Nankai Trough is extensively faulted in a compressional stress field due to subduction of the Philippine Sea plate. At the toe of the prism off Muroto, eastern Shikoku, closely-spaced heat flow measurements were made with a ROV and conspicuous high anomalies were found around the second frontal thrust, indicating that pore fluid flows upward along the fault (Kawada et al., 2014). Off the Kii peninsula, a large thrust fault system termed the megasplay cuts through the entire prism and its branches reach the seafloor. Yamano et al. (2014) conducted heat flow measurements with a surface ship across a branch of the megasplay and observed high heat flow values on the lower part of a fault scarp. Goto et al. (2008) made measurements with a submersible around biological communities along another branch of the megasplay and showed a sharp heat flow variation in a scale of several meters. These observations demonstrate that fluid flow along faults in various spatial scales can be detected by surface heat flow measurements.
The velocity or flux of vertical fluid flow may be estimated through long-term monitoring of temperature distribution in surface sediment. Temporal variation of the bottom water temperature propagates downward through sediment by thermal diffusion. Since this propagation process is affected by vertical fluid flow, analysis of long-term record of temperatures at multiple depths allows us to estimate fluid flow velocity (Goto et al., 2005). This method was applied to temperature records obtained in and around a biological community located a tip of the megasplay branch fault and the result indicates the existence of upward fluid flow (Kawada et al., 2013).