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Session: Real-Time Monitoring and Warning with Fiber Optic Seismology

Type: Oral

Date: 10/8/2024

Time: 03:00 PM

Room: Stanley Park Ballroom

Assessing Distributed Acoustic Sensing for Real-time Monitoring and Earthquake Early Warning (EEW) in the Southernmost Cascadia Subduction Zone

The southernmost Cascadia subduction zone presents considerable earthquake hazard from interplate and intraplate faults and is the most active region within the ShakeAlert EEW System’s reporting area. Both real-time performance assessments and offline simulations indicate that ShakeAlert would benefit from low-latency offshore seismic data in this region. To build towards this possibility, the USGS, Cal Poly Humboldt University, Luna Inc., and Seismics Unusual have begun a long-term effort to collect DAS data in this region to evaluate data quality and analysis methods. As a result of the Middle-Mile initiative and other partnerships, Cal Poly Humboldt’s campus is expected to be a regional hub for fiber optic cables in the coming years that cover the locked portion of the megathrust and dozens of active crustal faults. Since 2022, we have collected ~1.5 years of DAS data on a 15 km cable between Arcata and Eureka CA, including over 35 nearby earthquakes with magnitude estimates between 3.5 and 5.4, and over 400 earthquakes total. We are evaluating both real-time detection algorithms operating directly on the data acquisition system as well as algorithms for magnitude and location estimation. An automated detection algorithm running on the acquisition system detects M3 earthquakes by the time the P-wave has been recorded on about half the cable with a total latency of about 0.9 to 1.2 s between the first P-arrival on one end of the cable and the issuing of the detection. If the earthquake is within about 30 km from the cable, the detection is often issued before the first ShakeAlert message is published. By comparing with co-located nodal seismometer data, we have established the reliability of peak-strain measurements over four orders of magnitude. Magnitude estimates from peak-strain measurements and existing scaling relations are reliable once site effects are accounted for. We are investigating faster P-wave based magnitude estimates for warning applications, and future experiments will involve multiple cables and a variety of interrogators.

Presenting Author: Jeffrey

Additional Authors