title: Improved vertical optical fiber borehole strainmeter design for measuring Earth strain.
abstract: Fiber-based interferometers provide the means to sense very small displacements over long baselines, and have the advantage of being nearly completely passive in their operation, making them particularly well suited for geophysical applications. A new 250 m, interferometric vertical borehole strainmeter has been developed based completely on passive optical components. Details of the design and deployment at the Piñon Flat Observatory are presented. Power spectra show an intertidal noise level of -130 dB (re. 1 ϵ(2)/Hz), consistent within 1-3 dB between redundant components. Examination of its response to Earth tides and earthquakes relative to the areal strain recorded by an orthogonal pair of collocated, 730 m horizontal laser strainmeters yield a Poisson's ratio for local near surface material of 0.25 that is consistent with previous results.
authors.affiliation: Environmental Engineering and Earth Sciences, Clemson University, Clemson, South Carolina 29634-0919, USA.
authors.forename: Scott
authors.initials: S
authors.lastname: DeWolf
authors.affiliation: Institute of Geophysics and Planetary Physics, Scripps Institution of Oceanography University of California San Diego, 9500 Gilman Drive, MC 0225, La Jolla, California 92093-0225, USA.
authors.forename: Frank K
authors.initials: FK
authors.lastname: Wyatt
authors.affiliation: Institute of Geophysics and Planetary Physics, Scripps Institution of Oceanography University of California San Diego, 9500 Gilman Drive, MC 0225, La Jolla, California 92093-0225, USA.
authors.forename: Mark A
authors.initials: MA
authors.lastname: Zumberge
authors.affiliation: Institute of Geophysics and Planetary Physics, Scripps Institution of Oceanography University of California San Diego, 9500 Gilman Drive, MC 0225, La Jolla, California 92093-0225, USA.
authors.forename: William
authors.initials: W
authors.lastname: Hatfield