Superresolution of the urban subsurface using telecommunications fiber optic sensors

Eric Matzel, Gene A. Ichinose, Claire Doody, Rengin Gok, Jiun-Ting Lin, Christina Morency, & Justin Barno

Submitted August 30, 2026, SCEC Contribution #15559, 2026 SCEC Annual Meeting Poster #170

Telecommunications fiber-optic networks provide a widespread, high-bandwidth resource for distributed acoustic sensing (DAS), enabling unprecedented seismic sampling across urban environments. DAS collects detailed records of the complex urban wavefield including natural and anthropogenic sources. Interferometry converts that record into coherent signals suitable for high-resolution subsurface imaging.

Using an 80 km section of fiber in the San Francisco Bay Area (FUSE), we tested coda interferometry separately on two data sets: a local natural earthquake, and urban traffic. From both we are able to calculate coherent signals between discrete channels and invert those to produce high-resolution estimates of P and S wave velocity and attenuation.

The first dataset consisted of approximately 90 seconds of coda from a small earthquake near Tres Pinos, about 100 km south of the fiber. This broadband scattered energy, reverberating throughout the subsurface, enabled high-resolution imaging along the entire fiber and throughout the crust. The resulting models reveal interfaces associated with geological structures at depth. Variations in Vp/Vs and Qs/Qp show evidence for water infiltration near the Bay. Coda interferometry also resolved sharp features in the uppermost 100 m, including a 2 to 10 m thick, high-velocity layer associated with the built environment the fiber was emplaced in. Detailed lateral variations in the underlying very low-velocity sediments are particularly important for seismic-hazard assessment.

The second dataset consisted of urban traffic noise. Longer records were required for coherent signals to emerge from the background, with useful results obtained from 24 hours of data or more. These signals are typically higher in frequency than earthquake coda and propagate over distances of several kilometers, making them well suited for imaging and monitoring the shallow subsurface. Because traffic noise is persistent, this can be used for continuous near-surface monitoring.

The combination of telecommunications fiber, DAS, and interferometry offers a scalable approach for imaging and continuously monitoring the natural and built environment. Earthquake coda can support rapid, high-resolution imaging in tectonically active regions, while persistent anthropogenic sources allow comparable near-surface measures even in non-tectonic environments.

Key Words
DAS, interferometry, tomography, seismic hazard, san francisco bay

Citation
Matzel, E., Ichinose, G. A., Doody, C., Gok, R., Lin, J., Morency, C., & Barno, J. (2026, 08). Superresolution of the urban subsurface using telecommunications fiber optic sensors. Poster Presentation at 2026 SCEC Annual Meeting.

Related Projects & Working Groups
Applied Science Implementation (ASI)