Teleseisms and Microseisms on an Ocean-Bottom Distributed Acoustic Sensing Array

SUMMARY A collection of earthquake sources recorded at a single station, under specific conditions, are considered as a source array (SA), that is interpreted as if earthquake sources originate at the station location and are recorded at the source location. Then, array processing methods, that is array beamforming, are applicable to analyse the recorded signals. A possible application is to use source array multiple event techniques to locate and characterize near-source scatterers and structural interfaces. In this work the aim is to facilitate the use of earthquake source arrays by presenting an automatic search algorithm to configure the source array elements. We developed a procedure to search for an optimal source array element distribution given an earthquake catalogue including accurate origin time and hypocentre locations. The objective function of the optimization process can be flexibly defined for each application to ensure the prerequisites (criteria) of making a source array. We formulated four quantitative criteria as subfunctions and used the weighted sum technique to combine them in one single scalar function. The criteria are: (1) to control the accuracy of the slowness vector estimation using the time domain beamforming method, (2) to measure the waveform coherency of the array elements, (3) to select events with lower location error and (4) to select traces with high energy of specific phases, that is, sp- or ps-phases. The proposed procedure is verified using synthetic data as well as real examples for the Vogtland region in Northwest Bohemia. We discussed the possible application of the optimized source arrays to identify the location of scatterers in the velocity model by presenting a synthetic test and an example using real waveforms.

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“…Jousset et al 2018) and Ocean-Bottom Distributed Acoustic Sensing arrays (e.g. Williams et al 2019).…”

Section: Discussion a N D C O N C L U S I O N Smentioning

confidence: 99%

Earthquake source arrays: optimal configuration and applications in crustal structure studies

Karamzadeh

Heimann

Dahm

2020

Geophysical Journal International

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Section: Introductionmentioning

confidence: 99%

“…Recently, DAS has captured the attention of the geophysics community for seismic studies [11][12][13][14], and considerable research efforts are now aimed at addressing the demands of this new application space. Despite its recent adoption, however, there are plenty of demonstrations of its successful use in geophysical settings: from metropolitan areas [15] to near-shore deployments [13]. Nonetheless, environments demanding access to the full extent of ultra-long-haul telecommunication links are still mostly inaccessible through these technologies, which are limited to ∼100 km ranges despite remarkable efforts at range extension [16,17].…”

Section: Introductionmentioning

confidence: 99%

Mode-Walk-off Interferometry for Position-Resolved Optical Fiber Sensing

Costa

Zhan

Marandi

2023

J. Lightwave Technol.

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Simultaneously sensing and resolving the position of measurands along an optical fiber enables numerous opportunities, especially for application in environments where massive sensor deployment is not feasible. Despite significant progress in techniques based on round-trip time-of-flight measurements, the need for bidirectional propagation imposes fundamental barriers to their deployment in fiber communication links containing non-reciprocal elements. In this work, we break this barrier by introducing a position-resolved sensing technique based on the interference of two weaklycoupled non-degenerate modes of an optical fiber, as they walk-off through each other. We use this mode-walk-off interferometry to experimentally measure and localize physical changes to the fiber under test (axial strain and temperature) without the typical requirement of round-trip time-offlight measurements. The unidirectional propagation requirement of this method makes it compatible with fiber links incorporating non-reciprocal elements, uncovering a path for multiple sensing applications, including ultra-long range distributed sensing in amplified space-division-multiplexed telecommunication links.

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“…Dou et al 2017;Yu et al, 2019). Academic DAS applications in the underwater environment started in 2019 (Sladen et al 2019, Williams et al, 2019 with numerous observations -small local seismicity, large teleseismic earthquakes, surface gravity waves, microseismic noise-all with unprecedented spatial resolution. However, these studies focused on the low-frequency content of the DAS measurements, and the true potential of the approach at higher frequency than those used in seismology (!…”

Section: Introductionmentioning

confidence: 99%

Preliminary assessment of shipping noise monitoring using Distributed Acoustic Sensing on an optical fiber telecom cable

Rivet¹,

Cacqueray²,

Sladen³

et al. 2021

Preprint

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Distributed acoustic sensing (DAS) is a recent instrumental approach allowing to turn fiberoptic cables into dense arrays of acoustic sensors. This technology is attractive in marine environments where instrumentation is difficult to implement. A promising application is the monitoring of environmental and anthropic noise, leveraging existing telecommunication cables on the seafloor. We assess the ability of DAS to monitor such noise using a 41.5 kmlong cable offshore Toulon, France, focusing on a known and localized source. We analyze the noise emitted by the same tanker cruising above the cable, first 5.8 km offshore in 85 m deep bathymetry, and then 20 km offshore, where the seafloor is at a depth of 2000 m. The spectral analysis, the Doppler shift, and the apparent velocity of the acoustic waves striking the fiber allow us to separate the ship radiated noise from other noise. At 85 m water depth, the signal to noise ratio is high and the trajectory of the boat is recovered with beamforming analysis. At 2000 m water depth, although the acoustic signal of the ship is more attenuated, signals below 50 Hz are detected. These results confirm the potential of DAS applied to seafloor cables for remote monitoring of acoustic noise even at intermediate depth.

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Teleseisms and Microseisms on an Ocean-Bottom Distributed Acoustic Sensing Array

Cited by 7 publications

References 39 publications

Earthquake source arrays: optimal configuration and applications in crustal structure studies

Earthquake source arrays: optimal configuration and applications in crustal structure studies

Mode-Walk-off Interferometry for Position-Resolved Optical Fiber Sensing

Preliminary assessment of shipping noise monitoring using Distributed Acoustic Sensing on an optical fiber telecom cable

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