SCEC Award Number 16253 View PDF
Proposal Category Collaborative Proposal (Data Gathering and Products)
Proposal Title Enhancing Optical-Fiber Strainmeters for Earthquake Early Warning
Investigator(s)
Name Organization
Duncan Agnew University of California, San Diego Frank Wyatt University of California, San Diego Mark Zumberge University of California, San Diego
Other Participants
SCEC Priorities 2c, 5b, 6d SCEC Groups Geodesy, Transient Detection, Seismology
Report Due Date 03/15/2017 Date Report Submitted 04/20/2017
Project Abstract
 In this SCEC supported research, we focused on those characteristics of our Optical Fiber Strainmeter (OFS) design that must be improved to make it suitable for Earthquake Early Warning (EEW). In much the same way that strong-motion seismometers are needed because broadband seismometers clip during large events, a strainmeter designed for EEW must handle large, fast strains, rather than the normally targeted strain signals (e.g. tides, secular strain, and slow slip events).
An optical fiber can be strained to as much as 1% of its length, far more than adequate for transient earthquake strains, and allowing for a very wide dynamic range. The interferometer optics previously used to track the optical fiber’s length, however, were designed for precise strains that accumulate slowly. This SCEC support permitted making the improvements needed to track the faster signals.
Intellectual Merit OFSs are much less expensive to build and operate than other strainmeters and will allow broader coverage for studying earth structure. In addition to being useful to detect seismic and tidal strains, they offer an advantageous resource for the rapid characterization of large earthquakes, having the desirable characteristics of both strong-motion seismometers and fast-tracking GPS receivers. Their use in future EEW systems, especially in offshore environments, promises to provide an important complement to systems based on seismic sensing alone.
Broader Impacts This project serves to provide training of students in the new and rapidly developing area of fiber sensors for a range of geophysical purposes.
Exemplary Figure Figure 1. An overview of raw signals produced by an Optical Fiber Strainmeter (OFS) and the problem with aliasing at very large strain rates. The solution pursued here was the addition of an independent high-speed fringe counting system, complementary to the existent high-resolution fringe-tracking recording.