10:30 AM - 10:45 AM
[J07-2-01] New Technologies for Seafloor Deformation: Optical Fiber Strainmeters and Self-Calibrating Pressure Recorders
invited
We have advanced two new technologies for studying the deformation of the seafloor. The first is the measurement of strain using an optical fiber stretched horizontally across the seafloor. In October of 2015 we deployed a 200 m long optical fiber strainmeter at the toe of the accretionary prism of the Cascadia Subduction Zone off the coast of Oregon. The instrument was installed on the seafloor between two 100 kg anchors, tensioned, and operated continuously for 96 days. A temperature compensation scheme using two optical fibers with contrasting temperature responses allowed the separation of optical path length changes due to temperature from those due to strain. After removal of drift, an RMS noise level of 36 nanostrain over a one month record indicates the sensors will be useful for detecting slow slip events.
The second technology relies on seawater pressure as a proxy for height measurements. While time varying seafloor pressure can detect vertical motions with sub-centimeter precision, it is difficult to separate gauge drift from secular deformation. The Self-Calibrating Pressure Recorder (SCPR) was designed to circumvent the problem of gauge drift by employing an in situ deadweight calibrator to periodically provide a stable reference pressure to estimate and correct for gauge drift. One such instrument was deployed at Axial Volcano, collecting a continuous, drift-corrected recording of pressure for 17 months. In another experiment we are deploying an SCPR in campaign mode, collecting absolute pressure measurements at a series of seafloor benchmarks. We expect the method to yield epoch pressure values accurate to the equivalent of about 1 cm in height.
The second technology relies on seawater pressure as a proxy for height measurements. While time varying seafloor pressure can detect vertical motions with sub-centimeter precision, it is difficult to separate gauge drift from secular deformation. The Self-Calibrating Pressure Recorder (SCPR) was designed to circumvent the problem of gauge drift by employing an in situ deadweight calibrator to periodically provide a stable reference pressure to estimate and correct for gauge drift. One such instrument was deployed at Axial Volcano, collecting a continuous, drift-corrected recording of pressure for 17 months. In another experiment we are deploying an SCPR in campaign mode, collecting absolute pressure measurements at a series of seafloor benchmarks. We expect the method to yield epoch pressure values accurate to the equivalent of about 1 cm in height.