SCEC Award Number 14131 View PDF
Proposal Category Collaborative Proposal (Data Gathering and Products)
Proposal Title Routine Measurement of Seismic Strains: Analyzing and Improving Optical-Fiber Strainmeter Data
Investigator(s)
Name Organization
Duncan Agnew University of California, San Diego Mark Zumberge University of California, San Diego Frank Wyatt University of California, San Diego
Other Participants
SCEC Priorities 6d, 5b, 2c SCEC Groups Seismology, Geodesy, Transient Detection
Report Due Date 03/15/2015 Date Report Submitted N/A
Project Abstract
 This SCEC grant supports data analysis of the Trench Optical Fiber Strainmeter, or TOFS, installed at Pinyon Flat Observatory (PFO); this long-base instrument is much less expensive and easier to install than previous strainmeters, though relatively sensitive to temperature and lacking long-term stability. TOFS offers the prospects for the broad deployment of strainmeters for measurement of seismic strains.

Though SCEC funding for 2014 was not available until January, 2015, we nevertheless made good progress in 2014 year on understanding the recordings, leading to an NSF proposal for further development of the instrument.

With SCEC support we have compared data collected on two TOFS, 180 and 90 m long, installed parallel to the 730 m NWSE laser strainmeter (LSM) at PFO, examining relative noise levels and the relative sensitivity to seismic waves, microseisms, and tides. The instrument calibrations are all better than 1%; we observe systematic differences in the admittance between the systems that exceed this level, with the TOFS relative to the LSM being, in response to different signals, 5% or more above the expected value. We find the most plausible explanation to be that the underlying strain field must be slightly inhomogeneous, even for these long-wavelength signals, because of local variations in the rock. In 2015 we will be testing this using a third TOFS installed at a different azimuth.
Intellectual Merit The TOFS, being much less expensive to build, install, and operate, will allow much more widespread measurement of seismic and tidal strains, either for study of earth structure or as calibration for other strainmeter systems such as borehole strainmeters. They will also provide improved measurements of slow slip events (SSE's). which should produce new insights into the mechanism governing locking and unlocking of subduction zone and other faults. In conjunction with GPS, the availability of low-cost but highly sensitive and stable strainmeters, free of the expense of boreholes for installation, will enable much better characterization of the patterns of SSE's.
Broader Impacts This project will provide training of students in the new and developing area of fiber sensors for geophysical purposes.
Exemplary Figure Figure 4

Fiber strainmeter data in a temperature-stable borehole, which establishes that in a benign environment the fiber can provide relatively stable records at long periods.