Under this award, the PIs will undertake a pilot study of the interaction of tectonics and hydrogeology at the Nankai accretionary wedge of Japan. The study entails the deployment of five instruments for one year monitoring of cold seeps along the major coseismically active out-of-sequence thrust (OOST) zones. The PIs have been invited on a 3-week Japanese cruise that will investigate the seeps and deploy the instruments. These thrusts link directly down to the seismogenic zone, are known to leak fluids, and numerous seeps have been identified along them. Recent observations indicate that this OOST region is also the location from which very low frequency (VLF) earthquakes appear to be originating that may be tied to ultra slow earthquakes near the updip limit of the seismogenic zone. The PIs will be using instrumentation that has been shown to be capable of collecting long-term records of fluid flow, temperature, and both aqueous and gas chemistry in active seep environments. By comparing these flow records to nearby borehole seismic records (and perhaps Japanese OBS records), The PIs hope to clarify the relationship between subsurface fluid pressure pulses and stress release events related to the VLF events. The broader impacts of this study come primarily through its direct relevance to major international programs of research and natural hazard mitigation. The field area is the focus of a significant portion of IODPs NantroSeize drilling program. It is also intended to help initiate a highly collaborative partnership between US, and Japanese scientists. Eventually, the instrumentation we will be using can be networked as part of a long-term monitoring system. Studying fault instabilities in an earthquake and tsunami generating subduction zone has direct human and political impact.
