Distributed Acoustic Sensing from Hours to Milliseconds: Empirical Investigations of DAS Instrument Response

Session: Photonic Seismology [Poster]
Type: Poster
Date: 4/30/2020
Time: 08:00 AM
Room: Ballroom
Description: 

With the upside of high temporal and spatial sampling utilizing existing fiber-optic infrastructure, Distributed Acoustic Sensing (DAS) is in the process of revolutionising seismological data acquisition – especially in remote and urban areas, where a dense seismic network is otherwise hard to install.

Initial studies investigate the quality of DAS measurements along a single cable, showing data quality variations when compared to conventional seismometers. DAS data are influenced by site- and orientation effects and strongly affected by the transfer function between the propagation medium of the seismic waves and the fiber that is being interrogated. This transfer function can be obtained from comparisons with conventional seismometers – which is typically done in a narrow frequency band of interest. Because DAS measurements are theoretically sensitive to a wider frequency range than conventional instruments, there is a need to extend this narrow-band analysis to quantify the full potential of DAS measurements.

In this study, we analyse the DAS response within a frequency range from ~4000 s period to ~100 Hz, covering five orders of magnitude. The analyses are based on a range of experiments in Switzerland, including (1) active controlled-source experiments with co-located seismometers and geophones, (2) low-frequency strain induced by hydraulic injection in a borehole with co-located Fiber-Bragg-Grating (FBG) strain-meters, and (3) local to teleseismic ice- and earthquake recordings with co-located broadband stations.

We are able to quantify the amplitude and phase response of DAS recordings, and initial results suggest that the DAS recordings are sufficient for geophysical analyses such as full-waveform inversion, ambient noise tomography and event localisation. Even though the initial results look promising, we want to emphasize that further engagement by the DAS community is required to evaluate the DAS performance and repeatability among different study sites and interrogation units.

Presenting Author: Patrick Paitz

Authors