Sensing optical fibers for earthquake source characterization through DAS.

Distributed Acoustic Sensing (DAS) is establishing as a powerful approach for earthquake monitoring, turning fiber optic cables in dense spatial arrays able to retrieve almost continuous space-time records of seismic events. While tasks involving time measurements, such as phase picking, can be directly inherited from classical seismology, source characterization requires new methodologies grounded on unconventional quantities as recorded by DAS (strain or strain rate). DAS data show unique azimuthal sensitivity and enhance low-velocity waves trapped in the shallow layering beneath the fiber. Here we discuss and compare two alternative approaches for earthquake source parameter estimation. We either convert DAS data to kinematic quantities or develop a new mathematical formulation for modeling the radiation in the strain domain. Using data from a five-month DAS survey in the Southern Apennines tectonic environment, we characterized source parameters for microseismic events, using a frequency-domain probabilistic approach. We show the capability of DAS technology to depict the characteristic scales of seismic sources and earthquake seismic moment.