Improving active faults monitoring leveraging submarine telecom fiber optic cables : first results from central Chile

Subduction zones host some of the greatest diversity in seismic and aseismic fault slip behaviors, such as recurrent slow slip, non-volcanic tremors and repeating earthquakes, that are large enough to be measurable at the surface. Our understanding of the mechanisms leading to fault rupture, especially the role of aseismic slip is limited by the sparsity of instrumentation near the nucleation zone, which is predominantly located offshore away from permanent onland seismic networks.

Fiber-optic Distributed Acoustic Sensing (DAS) offers a new opportunity for long-term seismic observation of off-shore active faults by turning existing fiber-optic seafloor telecom cables into dense arrays of seismic and acoustic sensors. We conducted a one-month long DAS experiment on the northern leg of the Concón landing site of the Prat cable belonging to the GTD company. The longitudinal strain rate was recorded every 4m over a 150km-long fiber section at a temporal sampling rate of 125 Hz, which enabled us to measure low magnitude earthquakes and to locate them precisely. The earthquake catalog generated from the DAS data comprises more than 900 seismic events, which greatly extends the existing regional catalog. A preliminary analysis indicates that several seismic sequences are clustered in time and space, which include numerous events that cannot be detected by the onland seismological network. The ABYSS project will deploy this new observation tool continuously over several years, which will offer a new opportunity to better characterize the distribution of the seismicity in time and space, and will provide new constraints to the models of fault behavior during the seismic cycle. Combined with other types of analysis, such as seismic wave velocity changes monitoring at depth, these data will also provide additional constraints on the aseismic deformation of the fault zone.