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Measuring change in flow rate through a seep tapping a confined permeable formation is an inexpensive method for monitoring stress changes at depth.

Optical Tracer Injection System (OTIS) flow meters coupled to the seafloor measure inflow and outflow through cold seeps, and have the potential to detect aseismic deformation in the offshore environmnet. By deploying OTIS meters in conjunction with seismometers, heat flow and resistivity probes, we are attempting to learn the patters of fluid flow response as they reflect aseismic and seismic deformation. These studies to capture the hydrologic signature of slow earthquake events will help to constrain the geophysical and hydrogeologic interpretation of subduction zone processes.

"Hydronode" package collecting real-time data at the Nootka fault-Cascadia margin triple junction.
Seismicity in study area
click for larger image.

This study on the Nootka Fault at the Cascadia Margin of the Juan de Fuca plate is a collaborative effort with University of Washington and Woods Hole Oceanographic Institution, and is funded by National Science Foundation and the W.M. Keck Foundation. Check back for further real-time results at an upcoming Keck website.

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The Optical Tracer Injection System (OTIS), an electronic data logging version of the Chemical and Aqueous Transport (CAT) flow meter also developed in the Hydrogeology and Tectonics Studies Laboratory at the Scripps Institution of Oceanography, is designed for high resolution measurements in higher flow rate regimes, 0.2-1000m/yr, and has potential for real time data acquisition. Like the CAT meter (Tryon et al.,2001) the OTIS Meter measures aqueous flux at the seafloor by sealing around an area of the sediment surface and channeling the flow from this area through the instrument's flow tube. They differ, however, in the method of flow measurement. The OTIS, using the Persistor CF1 computer, injects 50uL pulses of fluorescent rhodamine tracer at 10-45 minute intervals into the flow tube, figure 1. The pulse of tracer will travel with the same velocity as the ambient flow through the flow tube. In the case of fluid discharge from the sediment, as displayed in figure 1, the tracer will flow out of the instrument past the upflow detection station. Alternatively the tracer may pass the downflow detection station during fluid recharge. In this manner, the OTIS can be used to determine flow rate in both upflow and downflow regimes. The computer records photodiode measurements of transmittance and fluorescence at both detection stations as an LED shines through the flow tube. In the case of the instrument currently collecting data on the Nootka fault intersecting the Cascadia margin, data is transmitted via satellite buoy or cable network.

CLICK HERE for a description of how to interpret OTIS meter data.

Figure 1: The Optical Flow Meter placed on sedimented seafloor focuses flow through a clear tube. Tracer is injected between downflow and upflow detection stations.