The GorDAS Distributed Acoustic Sensing Experiment Above the Cascadia Locked Zone and Subducted Gorda Slab

Abstract The southernmost portion of the Cascadia subduction zone in northern California produces high rates of moderate and large earthquakes owing to subduction of the Gorda slab and the deformation associated with the Mendocino Triple Junction. Distributed acoustic sensing (DAS) is rapidly advancing as a method for detecting earthquakes and imaging crustal structure. We have begun a long-term DAS monitoring experiment on buried telecom fiber in Arcata, California, to increase the available recordings of moderate-to-large earthquakes as well as image seismogenic structures. We have recorded over a year’s worth of data, including most aftershocks of the 2022 Mw 6.4 Ferndale earthquake, though not the mainshock itself. The dataset includes numerous magnitude 3.5 and larger earthquakes, including the 1 January 2023 Mw 5.4 Rio Dell earthquake. Here we present initial results comparing an earthquake detection algorithm, run in real time on the processing unit of the interrogator system, with both the ShakeAlert® earthquake early warning system and a postprocessed earthquake catalog developed with deep-learning phase-picker algorithms. The rapid onboard processing of the detector demonstrates the potential utility of DAS-based edge computing for earthquake early warning. We also verify the quality of the strain waveforms both in terms of peak amplitudes and waveform similarity using about five months of nodal seismometer data. These instruments were deployed roughly every 300 m along the ∼15-km-long cable and validate large variations in peak strain over short distances that are seen in the DAS data. All data from time windows surrounding both the local and teleseismic earthquakes are publicly available, which will improve our understanding of both the performance of DAS systems in moderate earthquakes and earthquake hazards associated with the Gorda subduction zone.