Abstract
Sparse seismic instrumentation in the oceans limits our understanding of deep Earth dynamics and submarine earthquakes. Distributed acoustic sensing (DAS), an emerging technology that converts optical fiber to seismic sensors, allows us to leverage pre-existing submarine telecommunication cables for seismic monitoring. Here we report observations of microseism, local surface gravity waves, and a teleseismic earthquake along a 4192-sensor ocean-bottom DAS array offshore Belgium. We observe in-situ how opposing groups of ocean surface gravity waves generate double-frequency seismic Scholte waves, as described by the Longuet-Higgins theory of microseism generation. We also extract P- and S-wave phases from the 2018-08-19 {M}_{w}8.2 Fiji deep earthquake in the 0.01-1 Hz frequency band, though waveform fidelity is low at high frequencies. These results suggest significant potential of DAS in next-generation submarine seismic networks.
Highlights
Sparse seismic instrumentation in the oceans limits our understanding of deep Earth dynamics and submarine earthquakes
We first examine ocean surface gravity waves and associated seismic modes directly observed on an ocean-bottom Distributed acoustic sensing (DAS) array offshore Zeebrugge, Belgium, which we interpret as evidence of in situ microseism generation
We argue that ocean surface gravity waves and Scholte waves observed on the Belgium DAS array (BDASA) at double-frequency (0.18 and 0.36 Hz, respectively) together represent in situ microseism generation following the theory of Longuet-Higgins[30]
Summary
Sparse seismic instrumentation in the oceans limits our understanding of deep Earth dynamics and submarine earthquakes. Distributed acoustic sensing (DAS), an emerging technology that converts optical fiber to seismic sensors, allows us to leverage pre-existing submarine telecommunication cables for seismic monitoring. We report observations of microseism, local surface gravity waves, and a teleseismic earthquake along a 4192-sensor ocean-bottom DAS array offshore Belgium. We extract P- and S-wave phases from the 2018-08-19 Mw8:2 Fiji deep earthquake in the 0.01-1 Hz frequency band, though waveform fidelity is low at high frequencies These results suggest significant potential of DAS in next-generation submarine seismic networks. We demonstrate that submarine horizontal DAS arrays utilizing pre-existing ocean-bottom fiber optic cables are effective for seismological studies and can record pressure perturbations from ocean wave phenomena. We discuss implications for future DAS deployments in marine settings
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