Alan F. Baird

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Ocean Space Surveillance and Real-Time Event Characterization Using Distributed Acoustic Sensing on Submarine Networks

Seismological Research Letters (2025)

Alan F. Baird Jan Petter Morten Volker Øye Steinar Bjørnstad

Abstract Distributed acoustic sensing (DAS) can be deployed on existing submarine fiber-optic cables to add long-range sensor capability to the cable infrastructure. In this article, we present the following: (1) observations and analysis of impulsive source events from long-term DAS measurements on a North Sea submarine telecommunications cable. The observations include local earthquakes originating in the crust below the cable, underwater explosions originating in the water column, an onshore explosion from the nearby coast, and examples of sonic booms from supersonic aircraft and a suspected meteor from the atmosphere. The analysis reveals how the signals from earthquakes and underwater/aerial explosions can be distinguished in the data domain based on their frequency and apparent velocity characteristics. (2) A processing workflow enabling real-time marine surveillance including detection and location of explosions in the water column. The processing is verified by corroborating local earthquakes and underwater explosions with independent data sources. We show that different types of waves can be identified including seismic body waves, hydroacoustic waves, and atmospheric infrasound waves coupled through the water column. Tracking the travel-time moveout along the nonstraight cable route allows for positioning of the source, which we demonstrate by migration stacking of the recorded signal. Signal processing suitable for real-time classification and source location is applied to the recorded data and shows how ocean space surveillance at scale can be realized.

10.1785/0220240360

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Application of machine learning to microseismic event detection in distributed acoustic sensing data

Geophysics (2020)

A. Stork Alan F. Baird Steve Horne G. Naldrett Sacha Lapins

This study presents the first demonstration of the transferability of a convolutional neural network (CNN) trained to detect microseismic events in one fiber-optic distributed acoustic sensing (DAS) data set to other data sets. DAS increasingly is being used for microseismic monitoring in industrial settings, and the dense spatial and temporal sampling provided by these systems produces large data volumes (approximately 650 GB/day for a 2 km long cable sampling at 2000 Hz with a spatial sampling of 1 m), requiring new processing techniques for near-real-time microseismic analysis. We have trained the CNN known as YOLOv3, an object detection algorithm, to detect microseismic events using synthetically generated waveforms with real noise superimposed. The performance of the CNN network is compared to the number of events detected using filtering and amplitude threshold (short-term average/long-term average) detection techniques. In the data set from which the real noise is taken, the network is able to detect >80% of the events identified by manual inspection and 14% more than detected by standard frequency-wavenumber filtering techniques. The false detection rate is approximately 2% or one event every 20 s. In other data sets, with monitoring geometries and conditions previously unseen by the network, >50% of events identified by manual inspection are detected by the CNN.

Microseism

Data set

10.1190/geo2019-0774.1

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Citations (72)

Transtensional deformation of Montserrat revealed by shear wave

Alan F. Baird J. M. Kendall Ralph A. Stephen J. Sparks Brian Baptie

a b s t r a c t Here we investigate seismic anisotropy of the upper crust in the vicinity of Soufriere Hills volcano using shear wave splitting (SWS) analysis from volcano-tectonic (VT) events. Soufriere Hills, which is located on the island of Montserrat in the Lesser Antilles, became active in 1995 and has been erupting ever since with five major phases of extrusive activity. We use data recorded on a network of seismometers between 1996 and 2007 partially spanning three extrusive phases. Shear-wave splitting in the crust is often assumed to be controlled either by structural features, or by stress aligned cracks. In such a case the polarization of the fast shear wave (φ) would align parallel to the strike of the structure, or to the maximum compressive stress direction. Previous studies analyzing SWS in the region using regional earthquakes observed temporal variations in φ which were interpreted as being caused by stress perturbations associated with pressurization of a dyke. Our analysis, which uses much shallower sources and thus only samples the anisotropy of the upper few kilometres of the crust, shows no clear temporal variation. However, temporal effects cannot be ruled out, as large fluctuations in the rate of VT events over the course of the study period as well as changes in the seismic network configuration make it difficult to assess. Average delay times of approximately 0.2 s, similar in magnitude to those reported for much deeper slab events, suggest that the bulk of the anisotropy is in the shallow crust. We observe clear spatial variations in anisotropy which we believe are consistent with structurally controlled anisotropy resulting from a left-lateral transtensional array of faults which crosses the volcanic complex.

Extrusive

Shear wave splitting

Seismometer

Stress field

S-wave

Source

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Field measurements of fracture characteristics on a wave-cut platform

Interpretation (2021)

Thomas Loriaux James P. Verdon J. M. Kendall Alan F. Baird James Wookey

We have used seismic refraction surveys of a wave-cut platform from a field site in South West England to characterize the impact of natural fracture networks on seismic velocities and anisotropy. Time-lapse surveys were performed as the high tide ebbed to investigate the seismic effects of the water draining from the rock. We also deployed a drone to map the fracture sets from the air. Azimuthal variations in the P- and S-wave velocities reflect the orientation of the main east–west-oriented joint set. Seismic velocities increased as the water drained, an effect attributed to a reduction in the effective density of the medium. The ratio of fracture normal ([Formula: see text]) to tangential ([Formula: see text]) compliance ([Formula: see text]), which can be used as a proxy for fracture saturation and permeability, was observed to increase from [Formula: see text] to [Formula: see text], primarily driven by a drop in [Formula: see text]. These variations are attributed to a decrease in the water content of the main fracture set as the tide retreats.

Saturation (graph theory)

Seismic anisotropy

10.1190/int-2020-0132.1

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Deformation in Rutford Ice Stream, West Antarctica: measuring shear-wave anisotropy from icequakes

Annals of Glaciology (2013)

Sophie Harland J. M. Kendall G. W. Stuart Geoffrey E. Lloyd Alan F. Baird

Abstract Ice streams provide major drainage pathways for the Antarctic ice sheet. The stress distribution and style of flow in such ice streams produce elastic and rheological anisotropy, which informs ice-flow modelling as to how ice masses respond to external changes such as global warming. Here we analyse elastic anisotropy in Rutford Ice Stream, West Antarctica, using observations of shear-wave splitting from three-component icequake seismograms to characterize ice deformation via crystal-preferred orientation. Over 110 high-quality measurements are made on 41 events recorded at five stations deployed temporarily near the ice-stream grounding line. To the best of our knowledge, this is the first well-documented observation of shear-wave splitting from Antarctic icequakes. The magnitude of the splitting ranges from 2 to 80 ms and suggests a maximum of 6% shear-wave splitting. The fast shear-wave polarization direction is roughly perpendicular to ice-flow direction. We consider three mechanisms for ice anisotropy: a cluster model (vertical transversely isotropic (VTI) model); a girdle model (horizontal transversely isotropic (HTI) model); and crack-induced anisotropy (HTI model). Based on the data, we can rule out a VTI mechanism as the sole cause of anisotropy – an HTI component is needed, which may be due to ice crystal a -axis alignment in the direction of flow or the alignment of cracks or ice films in the plane perpendicular to the flow direction. The results suggest a combination of mechanisms may be at play, which represent vertical variations in the symmetry of ice crystal anisotropy in an ice stream, as predicted by ice fabric models.

Pressure ridge

Shear wave splitting

10.3189/2013aog64a033

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Citations (29)

Characteristics of microseismic data recorded by distributed acoustic sensing systems in anisotropic media

Geophysics (2020)

Alan F. Baird A. Stork Steve Horne G. Naldrett J. M. Kendall

Fiber-optic distributed acoustic sensing (DAS) cables are now used to monitor microseismicity during hydraulic-fracture stimulations of unconventional gas reservoirs. Unlike geophone arrays, DAS systems are sensitive to uniaxial strain or strain rate along the fiber direction and thus provide a 1C recording, which makes identifying the directionality and polarization of incoming waves difficult. Using synthetic examples, we have shown some fundamental characteristics of microseismic recordings on DAS systems for purposes of hydraulic fracture monitoring in a horizontal well in anisotropic (vertical transverse isotropy [VTI]) shales. We determine that SH arrivals dominate the recorded signals because their polarization is aligned along the horizontal cable at the near offset, although SV will typically dominate for events directly above or below the array. The amplitude of coherent shear-wave (S-wave) arrivals along the cable exhibits a characteristic pattern with bimodal peaks, the width of which relates to the distance of the event from the cable. Furthermore, we find that S-wave splitting recorded on DAS systems can be used to infer the inclination of the incoming waves, overcoming a current limitation of event locations that have constrained events to lie in a horizontal plane. Low-amplitude SV arrivals suggest an event depth similar to that of the DAS cable. Conversely, steep arrivals produce higher amplitude SV-waves, with S-wave splitting increasing with offset along the cable. Finally, we determine how polarity reversals observed in the P and SH phases can be used to provide strong constraints on the source mechanisms.

Microseism

Geophone

10.1190/geo2019-0776.1

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Citations (40)

Using shear-wave splitting to assess strong anisotropy in a shale-gas reservoir and its relation to lithology, texture and fractures

EGUGA (2017)

Alan F. Baird J. M. Kendall Jessica Budge

Lithology

Shear wave splitting

Texture (cosmology)

Source

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Linking stress field deflection to basement structures in southern Ontario: Results from numerical modelling

Tectonophysics (2007)

Alan F. Baird Stephen D. McKinnon

Stress field

10.1016/j.tecto.2006.12.002

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Citations (4)

Stress Channelling and Partitioning of Seismicity in the Charlevoix Seismic Zone, Canada

AGU Fall Meeting Abstracts (2007)

Alan F. Baird Stephen D. McKinnon Laurent Godin

Channelling

Source

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Modeling uncertainty in P-wave arrival-times retrieved from DAS data: case-studies from 15 fiber optic cables

Geophysical Journal International (2024)

Emanuele Bozzi Nicola Piana Agostinetti Andreas Fichtner Sara Klaasen Arantza Ugalde

SUMMARY Distributed acoustic sensing (DAS) technology enables the detection of waves generated by seismic events, generally as uniaxial strain/strain rate time-series observed for dense, subsequent, portions of a Fibre Optic Cable (FOC). Despite the advantages in measurement density, data quality is often affected by uniaxial signal polarization, site effects and cable coupling, beyond the physical energy decay with distance. To better understand the relative importance of these factors for data inversion, we attempt a first modelling of noise patterns affecting DAS arrival times for a set of seismic events. The focus is on assessing the impact of noise statistics, together with the geometry of the problem, on epicentral location uncertainties. For this goal, we consider 15 ‘real-world’ cases of DAS arrays with different geometry, each associated with a seismic event of known location. We compute synthetic P-wave arrival times and contaminate them with four statistical distributions of the noise. We also estimate P-wave arrival times on real waveforms using a standard seismological picker. Eventually, these five data sets are inverted using a Markov chain Monte Carlo method, which offers the evaluation of the relative event location differences in terms of posterior probability density (PPD). Results highlight how cable geometry influences the shape, extent and directionality of the PPDs. However, synthetic tests demonstrate how noise assumptions on arrival times often have important effects on location uncertainties. Moreover, for half of the analysed case studies, the observed and synthetic locations are more similar when considering noise sources that are independent of the geometrical characteristics of the arrays. Thus, the results indicate that axial polarization, site conditions and cable coupling, beyond other intrinsic features (e.g. optical noise), are likely responsible for the complex distribution of DAS arrival times. Overall, the noise sensitivity of DAS suggests caution when applying geometry-only-based approaches for the a priori evaluation of novel monitoring systems.

Inverse theory

Arrival time

10.1093/gji/ggae364

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Citations (2)