Teleseisms and Microseism Generation Observed by an Ocean-Bottom Distributed Acoustic Sensing Array Offshore Belgium

Date: 4/24/2019

Time: 04:30 PM

Room: Grand Crescent

In just the last five years, distributed acoustic sensing (DAS) technology, which converts an optical fiber into a dense array of linear strainmeters, has emerged as a promising technology for earthquake seismology applications. Here, we demonstrate that DAS arrays repurposing pre-existing fibers laid in ocean-bottom telecommunication cables represent a valuable tool for marine seismology, with real-time data telemetry, unlimited deployment duration, and relatively low cost per sensor compared to current ocean-bottom seismometers. In August 2018, we occupied 42 km of fiber in a submarine cable offshore Belgium with a chirped DAS system, recording at 10 Hz with 4192 channels and 10 m spacing. Transforming the raw strain records into the frequency-wavenumber domain, we utilize phase information to identify and separate energy from seismic waves and ocean waves. Below 0.1 Hz, we successfully recover S-wave phases from the M8.2 2018-08-19 Fiji deep earthquake, which show moderate to high waveform fidelity when compared with a nearby broadband station. We observe ocean surface gravity waves propagating both land-ward and sea-ward across the array with a dominant period of 5.5 s. Further, we observe Scholte waves with a dominant period of 2.75 s and phase velocity around 500 m/s, which we determine are generated in-situ based on the symmetry of their directional spectrum. We discuss the implications of our observations for physical models of secondary microseism generation.

Presenting Author: Ethan F. Williams

Authors