A variety of surface waves in ocean-bottom DAS records

2021 ◽  
Author(s):  
Zack Spica ◽  
Loïc Viens ◽  
Jorge Castillo Castellanos ◽  
Takeshi Akuhara ◽  
Kiwamu Nishida ◽  
...  
Keyword(s):  
Surface Wave ◽  
Acoustic Waves ◽  
Fiber Optic ◽  
Acoustic Noise ◽  
Seismic Exploration ◽  
Ocean Bottom ◽  
Wide Range ◽  
Ocean Layer ◽  
Noise Cross Correlation ◽  
Low Amplitude

<p>Distributed acoustic sensing (DAS) can transform existing telecommunication fiber-optic cables into arrays of thousands of sensors, enabling meter-scale recordings over tens of kilometers. Recently, DAS has demonstrated its utility for many seismological applications onshore. However, the use of offshore cables for seismic exploration and monitoring is still in its infancy.<br>In this work, we introduce some new results and observations obtained from a fiber-optic cable offshore the coast of Sanriku, Japan. In particular, we focus on surface wave retrieved from various signals and show that ocean-bottom DAS can be used to extract dispersion curves (DC) over a wide range of frequencies. We show that multi-mode DC can be easily extracted from ambient seismo-acoustic noise cross-correlation functions or F-K analysis. Moderate magnitude earthquakes also contain multiple surface-wave packets that are buried within their coda. Fully-coupled 3-D numerical simulations suggest that these low-amplitude signals originate from the continuous reverberations of the acoustic waves in the ocean layer. </p>

First deployment of a 6-km long fiber-optic strain cable and a seafloor geodetic network, across an active submarine fault (offshore Catania, Sicily): The FOCUS experiment

2021 ◽  
Author(s):  
Marc-Andre Gutscher ◽  
Jean-Yves Royer ◽  
Shane Murphy ◽  
Frauke Klingelhoefer ◽  
Giovanni Barreca ◽  
...  
Keyword(s):  
Fiber Optic ◽  
Geodetic Network ◽  
Time Domain Reflectometry ◽  
Integrated System ◽  
Ocean Bottom ◽  
Fiber Optic Cable ◽  
Physics Institute ◽  
The North ◽  
Wide Range ◽  
Laser Reflectometry

<p>For the first time, a 6-km long fiber-optic strain cable was deployed across an active fault on the seafloor with the aim to monitor possible tectonic movement using laser reflectometry, 25 km offshore Catania Sicily (an urban area of 1 million people). Brillouin Optical Time Domain Reflectometry (BOTDR) is commonly used for structural health monitoring (bridges, dams, etc.) and under ideal conditions, can measure small strains (10<sup>-6</sup>) along a fiber-optic cable, across very large distances (10 - 200 km), with a spatial resolution of 10 - 50 m. The FocusX1 expedition, (6-21 October 2020) onboard the R/V Pourquoi Pas? was the first experiment of the European funded FOCUS project (ERC Advanced Grant). We first performed micro-bathymetric mapping and a video camera survey using the ROV Victor6000 to select the best path for the cable track and for deployment sites for eight seafloor geodetic stations. Next we connected a custom designed 6-km long fiber-optic cable (manufactured by Nexans Norway) to the TSS (Test Site South) seafloor observatory in 2100 m water depth operated by INFN-LNS (Italian National Physics Institute) via a new Y-junction frame and cable-end module. Cable deployment was performed by means of a deep-water cable-laying system with an integrated plow (updated Deep Sea Net design Ifremer, Toulon) to bury the cable 20 cm in the soft sediments in order to increase coupling between the cable and the seafloor. The cable track crosses the North Alfeo Fault at four locations. Laser reflectometry measurements began on 18 October 2020 and are being calibrated by a 3 - 4 year deployment of eight seafloor geodetic instruments (Canopus acoustic beacons manufactured by iXblue) deployed on 15 October 2020. During a future marine expedition, tentatively scheduled for early 2022 (FocusX2) a passive seismological experiment is planned to record regional seismicity. This will involve deployment of a temporary network of Ocean Bottom Seismometers (OBS) on the seafloor and seismic stations on land, supplemented by INGV permanent land stations. The simultaneous use of laser reflectometry, seafloor geodetic stations as well as seismological land and sea stations will provide an integrated system for monitoring a wide range of slipping event types along the North Alfeo Fault (e.g. - creep, slow-slip, rupture). A long-term goal of the project is the development of dual-use telecom cables with industry partners.</p>

scholarly journals Very Broadband Strain-Rate Measurements Along a Submarine Fiber-Optic Cable Off Cape Muroto, Nankai Subduction Zone, Japan

2020 ◽  
Author(s):  
Satoshi Ide ◽  
Eiichiro Araki ◽  
Hiroyuki Matsumoto
Keyword(s):  
Subduction Zone ◽  
Fiber Optic ◽  
Ocean Current ◽  
Small Scale ◽  
Ocean Bottom ◽  
Fiber Optic Cable ◽  
Deep Ocean Water ◽  
Wide Range ◽  
Rapid Temperature ◽  
Nankai Subduction Zone

Abstract Distributed acoustic sensing (DAS) is a new method that measures the strain change along a fiber-optic cable and has emerged as a promising geophysical application across a wide range of research and monitoring. Here we present the results of DAS observations from an submarine cable offshore Cape Muroto, Nankai subduction zone, western Japan. The observed signal amplitude varies widely among the DAS channels, even over short distances of only ~100 m, which is likely attributed to the differences in cable-seafloor coupling due to complex bathymetry along the cable route. Nevertheless, the noise levels at the well-coupled channels of DAS are almost comparable to those observed at nearby permanent ocean-bottom seismometers. Many earthquakes were observed during the five-day observation period, with the minimum and maximum detectable events being a local M1.1 event 30–50 km from the cable and a teleseismic Mw7.7 event that occurred in Cuba, respectively. Temperature appears to exert a greater control on the DAS signal than real strain in the quasi-static, sub-seismic range. We observed many rapid temperature change events migrating along the cable: a small number of large migration events (up to 10 km in 6 hours) associated with rapid temperature increases, and many small-scale events (both rising and falling temperatures). These events may reflect deep-ocean water mixing processes that are the result of ocean current–tidal interactions along an irregular seafloor boundary.

Distributed Acoustic Sensing Turns Fiber‐Optic Cables into Sensitive Seismic Antennas

2019 ◽  
Vol 91 (1) ◽  
pp. 1-15 ◽  
Author(s):  
Zhongwen Zhan
Keyword(s):  
Seismic Waves ◽  
Fiber Optic ◽  
Glass Fibers ◽  
Ocean Bottom ◽  
Thin Glass ◽  
Acoustic Sensing ◽  
Wide Range ◽  
Solar System Bodies ◽  
Distributed Acoustic Sensing ◽  
Seismic Networks

Abstract Distributed acoustic sensing (DAS) is a new, relatively inexpensive technology that is rapidly demonstrating its promise for recording earthquake waves and other seismic signals in a wide range of research and public safety arenas. It should significantly augment present seismic networks. For several important applications, it should be superior. It employs ordinary fiber‐optic cables, but not as channels for data among separate sophisticated instruments. With DAS, the hair‐thin glass fibers themselves are the sensors. Internal natural flaws serve as seismic strainmeters, kinds of seismic detector. Unused or dark fibers are common in fiber cables widespread around the globe, or in dedicated cables designed for special application, are appropriate for DAS. They can sample passing seismic waves at locations every few meters or closer along paths stretching for tens of kilometers. DAS arrays should enrich the three major areas of local and regional seismology: earthquake monitoring, imaging of faults and many other geologic formations, and hazard assessment. Recent laboratory and field results from DAS tests underscore its broad bandwidth and high‐waveform fidelity. Thus, while still in its infancy, DAS already has shown itself as the working heart—or perhaps ear drums—of a valuable new seismic listening tool. My colleagues and I expect rapid growth of applications. We further expect it to spread into such frontiers as ocean‐bottom seismology, glacial and related cryoseismology, and seismology on other solar system bodies.

scholarly journals The FOCUS experiment 2020 (Fiber Optic Cable Use for Seafloor studies of earthquake hazard and deformation)

2020 ◽  
Author(s):  
Marc-Andre Gutscher ◽  
Jean-Yves Royer ◽  
David Graindorge ◽  
Shane Murphy ◽  
Frauke Klingelhoefer ◽  
...  
Keyword(s):  
Fiber Optic ◽  
Earthquake Hazard ◽  
Test Site ◽  
Relative Displacement ◽  
Integrated System ◽  
Ocean Bottom ◽  
Physics Institute ◽  
The North ◽  
Wide Range ◽  
Laser Reflectometry

<p>Laser reflectometry (BOTDR), commonly used for structural health monitoring (bridges, dams, etc.), for the first time is being tested to study movements of an active fault on the seafloor, 25 km offshore Catania Sicily (an urban area of 1 million people). Under ideal conditions, this technique can measure small strains (10E-6), across very large distances (10 - 200 km) and locate these strains with a spatial resolution of 10 - 50 m. As the first experiment of the European funded FOCUS project (ERC Advanced Grant), in late April 2020 we aimed to connect and deploy a dedicated 6-km long strain cable to the TSS (Test Site South) seafloor observatory in 2100 m water depth operated by INFN-LNS (Italian National Physics Institute). The work plan for the marine expedition FocusX1 onboard the research vessel PourquoiPas? is described here. First, microbathymetric mapping and a video camera survey are performed by the ROV Victor6000. Then, several intermediate junction frames and short connector cables (umbilicals) are connected. A cable-end module and 6-km long fiber-optic strain cable (manufactured by Nexans Norway) is then connected to the new junction box. Next, we use a deep-water cable-laying system with an integrated plow (updated Deep Sea Net design Ifremer, Toulon) to bury the cable 20 cm in the soft sediments in order to increase coupling between the cable and the seafloor. The targeted track for the cable crosses the North Alfeo Fault at three locations. Laser reflectometry measurements began April 2020 and will be calibrated by a three-year deployment of seafloor geodetic instruments (Canopus acoustic beacons manufactured by iXblue) also started April 2020, to quantify relative displacement across the fault. During a future marine expedition, tentatively scheduled for 2021 (FocusX2) a passive seismological experiment is planned to record regional seismicity. This will involve deployment of a temporary network of OBS (Ocean Bottom Seismometers) on the seafloor and seismic stations on land, supplemented by INGV permanent land stations. The simultaneous use of laser reflectometry, seafloor geodetic stations as well as seismological land and sea stations will provide an integrated system for monitoring a wide range of types of slipping events along the North Alfeo Fault (e.g. - creep, slow-slip, rupture). A long-term goal is the development of dual-use telecom cables with industry partners.</p>

scholarly journals Novel Bloch wave excitation platform based on few-layer photonic crystal deposited on D-shaped optical fiber

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Esteban Gonzalez-Valencia ◽  
Ignacio Del Villar ◽  
Pedro Torres
Keyword(s):  
Optical Fibers ◽  
High Performance ◽  
Light Propagation ◽  
Fiber Optic ◽  
Layer Structure ◽  
Optical Network ◽  
Building Blocks ◽  
Bloch Wave ◽  
Nanophotonic Devices ◽  
Wide Range

AbstractWith the goal of ultimate control over the light propagation, photonic crystals currently represent the primary building blocks for novel nanophotonic devices. Bloch surface waves (BSWs) in periodic dielectric multilayer structures with a surface defect is a well-known phenomenon, which implies new opportunities for controlling the light propagation and has many applications in the physical and biological science. However, most of the reported structures based on BSWs require depositing a large number of alternating layers or exploiting a large refractive index (RI) contrast between the materials constituting the multilayer structure, thereby increasing the complexity and costs of manufacturing. The combination of fiber–optic-based platforms with nanotechnology is opening the opportunity for the development of high-performance photonic devices that enhance the light-matter interaction in a strong way compared to other optical platforms. Here, we report a BSW-supporting platform that uses geometrically modified commercial optical fibers such as D-shaped optical fibers, where a few-layer structure is deposited on its flat surface using metal oxides with a moderate difference in RI. In this novel fiber optic platform, BSWs are excited through the evanescent field of the core-guided fundamental mode, which indicates that the structure proposed here can be used as a sensing probe, along with other intrinsic properties of fiber optic sensors, as lightness, multiplexing capacity and easiness of integration in an optical network. As a demonstration, fiber optic BSW excitation is shown to be suitable for measuring RI variations. The designed structure is easy to manufacture and could be adapted to a wide range of applications in the fields of telecommunications, environment, health, and material characterization.

scholarly journals Reliable workflow for inversion of seismic receiver function and surface wave dispersion data: a “13 BB Star” case study

2019 ◽  
Vol 24 (1) ◽  
pp. 101-120
Author(s):  
Kajetan Chrapkiewicz ◽  
Monika Wilde-Piórko ◽  
Marcin Polkowski ◽  
Marek Grad
Keyword(s):  
Surface Wave ◽  
Inverse Problems ◽  
Receiver Function ◽  
Joint Inversion ◽  
Wave Dispersion ◽  
Receiver Functions ◽  
P Wave ◽  
Surface Wave Dispersion ◽  
Phase Velocity Dispersion ◽  
Wide Range

AbstractNon-linear inverse problems arising in seismology are usually addressed either by linearization or by Monte Carlo methods. Neither approach is flawless. The former needs an accurate starting model; the latter is computationally intensive. Both require careful tuning of inversion parameters. An additional challenge is posed by joint inversion of data of different sensitivities and noise levels such as receiver functions and surface wave dispersion curves. We propose a generic workflow that combines advantages of both methods by endowing the linearized approach with an ensemble of homogeneous starting models. It successfully addresses several fundamental issues inherent in a wide range of inverse problems, such as trapping by local minima, exploitation of a priori knowledge, choice of a model depth, proper weighting of data sets characterized by different uncertainties, and credibility of final models. Some of them are tackled with the aid of novel 1D checkerboard tests—an intuitive and feasible addition to the resolution matrix. We applied our workflow to study the south-western margin of the East European Craton. Rayleigh wave phase velocity dispersion and P-wave receiver function data were gathered in the passive seismic experiment “13 BB Star” (2013–2016) in the area of the crust recognized by previous borehole and refraction surveys. Final models of S-wave velocity down to 300 km depth beneath the array are characterized by proximity in the parameter space and very good data fit. The maximum value in the mantle is higher by 0.1–0.2 km/s than reported for other cratons.

THE OPTICAL PROPERTIES OF NITROGENATED AMORPHOUS CARBON FILMS GROWN BY A NOVEL SURFACE WAVE MICROWAVE PLASMA CVD METHOD

2004 ◽  
Vol 18 (18) ◽  
pp. 987-1001 ◽  
Author(s):  
M. RUSOP ◽  
S. ADHIKARI ◽  
A. M. M. OMER ◽  
S. ADHIKARY ◽  
H. UCHIDA ◽  
...  
Keyword(s):  
Optical Properties ◽  
Surface Wave ◽  
Amorphous Carbon ◽  
Annealing Temperature ◽  
Microwave Plasma ◽  
Chemical Vapor ◽  
Carbon Films ◽  
Cvd Method ◽  
Wide Range ◽  
Bonding Properties

The effects of annealing temperature on the optical properties of nitrogenated amorphous carbon (a-C:N) films grown on quartz substrates by a novel surface wave microwave plasma chemical vapor deposition (SWMP-CVD) method are reported. The thickness, optical, structural and bonding properties of the as-grown and anneal-treated a-C:N films were measured and compared. The film thickness decreased rapidly with increasing annealing temperature above 350°C. A wide range of optical absorption characteristics is observed, depending on the annealing temperature. The optical band gap of as-grown a-C:N films is approximately 2.8 eV, gradually decreasing to 2.5 eV for the films anneal-treated at 300°C, and beyond that decreasing rapidly down to 0.9 eV at 500°C. The Raman and FTIR spectroscopy measurements have shown that the structural and composition of the films can be tuned by optimizing the annealing temperature. The change of optical, structural and bonding properties of SWMP-CVD-grown a-C:N films with higher annealing temperature was attributed to the fundamental changes in the bonding and band structures of the films.

scholarly journals Testing Time and Frequency Fiber-Optic Link Transfer by Hardware Emulation of Acoustic-Band Optical Noise

2016 ◽  
Vol 23 (2) ◽  
pp. 309-316
Author(s):  
Marcin Lipiński ◽  
Przemysław Krehlik ◽  
Łukasz Śliwczyński ◽  
Łukasz Buczek ◽  
Jacek Kołodziej
Keyword(s):  
Fiber Optic ◽  
Data Transfer ◽  
Acoustic Noise ◽  
Mechanical Vibration ◽  
Low Frequency ◽  
Propagation Delay ◽  
Optical Signal ◽  
Testing Time ◽  
Optical Noise ◽  
Signal Phase

Abstract The low-frequency optical-signal phase noise induced by mechanical vibration of the base occurs in field-deployed fibers. Typical telecommunication data transfer is insensitive to this type of noise but the phenomenon may influence links dedicated to precise Time and Frequency (T&F) fiber-optic transfer that exploit the idea of stabilization of phase or propagation delay of the link. To measure effectiveness of suppression of acoustic noise in such a link, a dedicated measurement setup is necessary. The setup should enable to introduce a low-frequency phase corruption to the optical signal in a controllable way. In the paper, a concept of a setup in which the mechanically induced acoustic-band optical signal phase corruption is described and its own features and measured parameters are presented. Next, the experimental measurement results of the T&F transfer TFTS-2 system’s immunity as a function of the fibre-optic length vs. the acoustic-band noise are presented. Then, the dependency of the system immunity on the location of a noise source along the link is also pointed out.

scholarly journals Fiber Optic Attenuator

2021 ◽  
Vol 2086 (1) ◽  
pp. 012128
Author(s):  
D P Andreev ◽  
E I Andreeva
Keyword(s):  
Optical Fiber ◽  
Spectral Dependence ◽  
Fiber Optic ◽  
Dynamic Range ◽  
Wide Range ◽  
Bending Losses ◽  
Type Fiber

Abstract A study of a bending-type fiber-optic attenuator has been carried out. It is shown that the use of G.655 - optical fiber provides the largest dynamic range of the attenuator. The spectral dependence of the bending losses was measured in a wide range of wavelengths: from 1270 to 1610 nm.

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