Opportunities and challenges of fiber-optic seismology for permanent monitoring of subsurface processes

Biondo Biondi

Stanford University, Geophysics

Date & Time
Building 3, Rambo Auditorium
Andy Barbour

Continuous seismic monitoring can provide early warning of potentially
hazardous conditions developing in the subsurface, as well as useful information
on the flow of natural resources such as water and hydrocarbons. However, the
cost of continuous monitoring is a significant obstacle to its widespread
application. Distributed Acoustic Sensors (DAS) DAS arrays have the potential of
enabling cost-effective continuous and spatially dense seismic monitoring over
large areas. By leveraging the preexisting fiber infrastructure developed for
telecommunication purposes, we could build large seismic arrays under densely
populated cities around the world in a cost-effective way.

Starting the beginning of September 2016, we have been continuously recording
seismic data as sensed by a fiber-optic cable placed under Stanford University
campus and measured by an OptaSense DAS system. Our “Stanford Fiber
Seismic Observatory (S-FSO)” experiment aims at studying the feasibility of
using a DAS array that record data using a fiber-optic cable “free-floating” in a
PVC conduit buried in the ground. Coupling between the fiber cable and the
surrounding rocks relies exclusively on gravity and friction. Our array has
recorded hundreds of seismic events. Preliminary analysis of these events shows
that the recorded signal is highly repeatable and correlates well wit the data
recorded by a broadband seismometer located on campus. We are applying
ambient (mostly anthropogenic) noise interferometry to estimate and monitor
subsurface properties under the array. Data analysis has also prompted us to
develop new theoretical models to better interpret the recorded signal and the
interferometric data.

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