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Characterization of Urban Seismicity Using Multi-fiber Distributed Acoustic Sensing

Distributed Acoustic Sensing (DAS) enables dense seismic measurements in urban environments by repurposing existing telecommunication infrastructure. Athens presents an ideal setting, as Greece is among Europe's most seismically active countries, and the Athens metropolitan area lies within a geologically complex basin whose vulnerability was demonstrated by the destructive 1999 Mw 5.9 Parnitha earthquake. We present results from a multi-fiber DAS experiment conducted in Athens, Greece, from 16 May to 30 June 2025, using four telecommunication fibers provided by the Hellenic Telecommunications Organisation (OTE). Two interrogators simultaneously recorded data using the four fibers with lengths of approximately 24, 38, 42, and 48 km, providing extensive azimuthal coverage of Athens, which makes the study one of the largest urban DAS campaigns ever performed.

Data were acquired in two configurations, a lower spatial resolution mode optimized for earthquake recording and a higher resolution mode for ambient noise interferometry. To detect seismic events, we applied bandpass filtering followed by phase-weighted stacking across channels and STA/LTA (short-term average / long-term average) triggering to identify candidate events. During the acquisition period, the National Observatory of Athens recorded 2,645 events across the broader seismic network, of which 548 were detected on at least one fiber. Notably, the DAS array also recorded numerous small events not present in the NOA catalog. For nearby events, we pick P- and S-wave arrivals to constrain body-wave travel times. These picks are also used to locate events in the NOA catalog, which enables us to compare with network-derived hypocenters and allows us to assess potential improvement from the dense DAS coverage, before applying the approach to smaller events detected only by DAS. The travel-time data will also serve as input for 3D eikonal traveltime tomography to image subsurface velocity structure beneath metropolitan Athens.

Session: Fiber-Optic Sensing Applications in Seismology and Environmental Science [Poster]

Type: Poster

Room: Exhibit Hall A+B

Date: 4/17/2026

Presentation Time: 08:00 AM (local time)

Presenting Author: Andreas Fichtner

Student Presenter: No

Invited Presentation: 

Poster Number: 73

Additional Authors