HR: 1340h
AN: S53A-0189    [Abstracts]
TI: OTIS Flow Meter for Offshore Detection of Silent Earthquakes
AU: * LaBonte, A L
EM: alabonte@ucsd.edu
AF: Scripps Institution of Oceanography, Univ. of California San Diego 9500 Gilman Drive 0244, La Jolla, CA 92093-0244 United States
AU: Brown, K M
EM: kmbrown@ucsd.edu
AF: Scripps Institution of Oceanography, Univ. of California San Diego 9500 Gilman Drive 0244, La Jolla, CA 92093-0244 United States
AB: The Optical Tracer Injection System (OTIS) is a new marine flow meter developed for the novel application of measuring fluid flow rates sensitive to transient pore pressure gradients and volumetric strain. These meters are designed with the potential to detect aseismic deformation in the offshore environment. Upcoming empirical results from subduction zone studies in Cascadia and Costa Rica are to be processed with dislocation modeling. Knowing the role of fluids in aseismic and seismic events will help to characterize the earthquake cycle: what fraction of built up stress is released in the form of earthquakes vs. silent creep events, and in what sequence these events occur. While bore hole studies give significant insight to subsurface spatial and temporal pressure gradients, they are difficult to execute and costly. On the other hand, monitoring fluid flux at natural focused flow seep sites on the seafloor as an indicator of strain, like monitoring water level changes in well bore studies, is a cost efficient alternative. Coupled to the seafloor, the OTIS optically senses, and electronically logs, the concentration of injected fluorescent rhodamine tracer from which the rate of fluids flowing through the sediment water interface can be determined. It has been developed to detect a large range of flow rates at the sediment water interface, 0.01 to 500+ m/yr, at 5-30 minute temporal resolution. The OTIS is deployed in conjunction with an osmotic sampler for post-recovery chemical analyses of pore fluids expelled at seep sites. Initial instrument tests at cold seeps in Monterey Bay coincided with Chemical Aqueous Transport (CAT) meter results and confirm improved temporal resolution, and low sensitivity to ocean currents. Presently, an OTIS is placed at the toe of the Cascadia forearc at the triple junction with the Nootka transform fault as part of a modem package for uplink of real time data to a surface buoy. In conjunction with land based seismic and geodetic networks, offshore flow meters capturing a hydrologic signature slow earthquake events help to constrain the geophysical and hydrogeologic interpretation of subduction zone processes.
DE: 8045 Role of fluids
DE: 8123 Dynamics, seismotectonics
DE: 7209 Earthquake dynamics and mechanics
DE: 3094 Instruments and techniques
SC: Seismology [S]
MN: 2004 AGU Fall Meeting