HR: 0800h
AN: T21A-0440    [Abstracts]
TI: A Borehole Fiber-Optic Strainmeter
AU: * Zumberge, M A
EM: zumberge@ucsd.edu
AF: Institute of Geophysics and Planetary Physics, Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA 92093-0225 United States
AB: The SAFOD project provides an opportunity to study the basic mechanics of a fault that undergoes relatively frequent events. Magnitude 2 earthquakes within a few km of the borehole occur several times per year and produce strain signals on the order of a nanostrain. We installed a vertical fiber-optic strainmeter in the annulus of cement between the inner and outer casings of the borehole. The sensor consists of an optical fiber cable stretched from the surface to a depth of 864 m. The optical length of the fiber is monitored with a laser interferometer sampled at 50,000 samples per second. The strainmeter noise is about 0.01 nanostrain at 1 Hz, which provides clear records of coseismic offsets.
DE: 1209 Tectonic deformation (6924)
SC: Tectonophysics [T]
MN: Fall Meeting 2005