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.

scholarly journals Very broadband strain-rate measurements along a submarine fiber-optic cable off Cape Muroto, Nankai subduction zone, Japan

2021 ◽  
Vol 73 (1) ◽  
Author(s):  
Satoshi Ide ◽  
Eiichiro Araki ◽  
Hiroyuki Matsumoto
Keyword(s):  
Subduction Zone ◽  
Fiber Optic ◽  
Ocean Current ◽  
Small Scale ◽  
Distributed Temperature Sensing ◽  
Fiber Optic Cable ◽  
Deep Ocean Water ◽  
Wide Range ◽  
Rapid Temperature ◽  
Nankai Subduction Zone

AbstractDistributed 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 a 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, suggesting that the cable has the ability to detect nearby micro earthquakes and even tectonic tremors. Many earthquakes were observed during the 5-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, where we can regard our DAS record as distributed temperature sensing (DTS) record, and detected many rapid temperature change events migrating along the cable: a small number of large migration events (up to 10 km in 6 h) associated with rapid temperature decreases, and many small-scale events (both rising and falling temperatures). These events may reflect oceanic internal surface waves and deep-ocean water mixing processes that are the result of ocean current–tidal interactions along an irregular seafloor boundary.

scholarly journals Very broadband strain-rate measurements along a submarine fiber-optic cable off Cape Muroto, Nankai subduction zone, Japan

2021 ◽  
Author(s):  
Satoshi Ide ◽  
Eiichiro Araki ◽  
Hiroyuki Matsumoto
Keyword(s):  
Subduction Zone ◽  
Fiber Optic ◽  
Ocean Current ◽  
Small Scale ◽  
Distributed Temperature Sensing ◽  
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 a 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, suggesting that the cable has the ability to detect nearby micro earthquakes and even tectonic tremors. 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, where we can regard our DAS record as distributed temperature sensing (DTS) record, and detected 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 decreases, and many small-scale events (both rising and falling temperatures). These events may reflect oceanic internal surface waves and deep-ocean water mixing processes that are the result of ocean current–tidal interactions along an irregular seafloor boundary.

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>

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>

Bending Performance of Fiber-Optic Cable Sheaths: Application of New Apparatus and Techniques

1982 ◽  
Vol 104 (3) ◽  
pp. 578-586 ◽  
Author(s):  
M. R. Santana ◽  
G. M. Yanizeski
Keyword(s):  
Fiber Optic ◽  
Bending Stiffness ◽  
Fiber Optic Cable ◽  
Cross Sectional ◽  
Bending Performance ◽  
Wide Range ◽  
Tensile Performance ◽  
New Apparatus ◽  
Reinforced Fiber ◽  
As Stress

Apparatus and techniques were developed by which moment-curvature curves can be generated over a wide range of curvatures, cable diameters, and environmental conditions. The resulting curves can be used to analyze bending performance in the same way as stress-strain curves are used to analyze tensile performance. In the first series of tests using this apparatus, five wire-reinforced fiber-optic cable sheaths were tested at room temperature. The wire reinforcement had a dominant, theoretically predictable effect on the bending stiffness of certain designs, while it was relatively unimportant in others. The key difference is the degree of encapsulation of the reinforcement, which can be controlled by simple changes in design. In addition, buckling performance can be improved by increasing the cross-sectional rigidity. In both cases, tensile performance is relatively unaffected. These findings are exemplified by the performances of a single-ply and a crossply design. Compared to the single ply, the crossply has the more rigid cross section and the lower degree of encapsulation. Both sheaths have nearly equal bending stiffness throughout the entire range of curvature, and the buckling radius of the crossply design (7.4 cm) is better than that of the single-ply design (8.4 cm) despite a 2 to 1 advantage in tensile stiffness. An effective design sequence has evolved from the results of this study: (a) select reinforcement for tensile performance, (b) adjust cross-sectional rigidity for buckling performance, and (c) adjust reinforcement encapsulation for bending stiffness performance. In this sequence, each step is nearly independent of the others.

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>

UTILIZING ULTRASONIC AND PULSED-EDDY CURRENT TECHNOLOGIES TO MAP THE LOCATION OF FIBER-OPTIC CABLE AND CLAMPS: A CASE STUDY

2021 ◽  
Author(s):  
Roddy Hebert ◽  
◽  
Rojelio Medina ◽  
JC Pinkett ◽  
Tyler Costa ◽  
...  
Keyword(s):  
Eddy Current ◽  
Fiber Optic ◽  
Current System ◽  
Value Added ◽  
Fiber Optic Cable ◽  
Ultrasonic Scanning ◽  
Service Companies ◽  
Pulsed Eddy Current ◽  
Wide Range ◽  
Great Insight

In an ongoing attempt to learn more about subsurface conditions before and during production, service companies and operators have explored a wide range of technologies. One technology, that allows for transmission of subsurface data back to the surface, is the installment of fiber optic cable behind casing. Fiber optic cable not only provides subsurface data conditions affecting production, but it serves as a highway for data transmission in seismic surveys, as well as, monitoring production information itself along the entire length of the cable. We will expand on methods used to preserve this installment of the fiber optic cable by identifying its location behind casing. Circumferential ultrasonic scanning techniques have been used for many years to inspect the casing itself, and cement behind the first string of casing. These techniques offer a better inspection of channeling, or partial vertical void in cement behind first string of casing, than just your standard radial cement bond tool. Cement and Casing Inspection have been useful services of the ultrasonic scanning services, but it isn’t without limitations, whereas this scanning tool has a shallow depth of investigation. Traditionally, standard cement bond logs are used in conjunction with the circumferential ultrasonic scanning services to examine the bond index, and to offer some additional understanding of the cement bond to casing, as well as cement to formation bond. In that shallow ultrasonic scan, is where this publication will demonstrate the value added of locating the fiber optic cable, but it is not without some uncertainty. To reduce some of that uncertainty, a pulsed-eddy current system, which uses an arm-mounted pad sensor that contacts the inside of the first casing string, utilizes pulsed-eddy current technology to accurately locate the position of the fiber optic cable mounting clamps. Detecting the location of the clamps, offers great insight into oriented perforation, but as this publication will demonstrate, the fiber optic cable can meander in between those clamps. The circumferential ultrasonic scanning service offers visibility of the meandering of that fiber optic cable, in between clamps, and when used in combination with the pulsed-eddy current system, this creates an integrated service that reduces the probability of perforating the installment of the fiber optic cable. Purpose of this paper, will be, to demonstrate the use of the impedance data, gained from the circumferential ultrasonic scanning tool, in combination with the fiber optic clamp location from the pulsed-eddy current tool, to locate the fiber optic flatpack between clamp locations. However, there are limitations in the location of the fiber flatpack, as in, gaps between flatpack and casing, and/or lack of cement coverage. The final product will include the depth location of clamps, station degrees of fiber loop, degrees of fiber flatpack location, and level of confidence by interval shading. This information will give customers greater confidence in the execution of oriented perforation procedures, without damaging fiber optic cable flatpack.

Turning a Telecom Fiber-Optic Cable into an Ultradense Seismic Array for Rapid Postearthquake Response in an Urban Area

2021 ◽  
Author(s):  
Xiangfang Zeng ◽  
Feng Bao ◽  
Clifford H. Thurber ◽  
Rongbing Lin ◽  
Shuofan Wang ◽  
...  
Keyword(s):  
Ground Motion ◽  
Early Warning ◽  
Fiber Optic ◽  
Small Scale ◽  
Monitoring Networks ◽  
Motion Pattern ◽  
Fiber Optic Cable ◽  
Epicentral Area ◽  
Distributed Acoustic Sensing ◽  
Deployment Time

Abstract Aftershock-monitoring networks deployed in the epicentral area of a damaging earthquake play important roles in earthquake early warning and ShakeMap estimation, which contribute to hazard mitigation. Using distributed acoustic sensing (DAS) technology with dark fiber can significantly reduce deployment time and cost, and improve spatial sampling, both of which help capture more aftershocks. In this study, we used a 7.6 km dark fiber in Tangshan, China, to monitor seismicity after the 12 July 2020 Ms 5.1 earthquake. The DAS array detected dozens of earthquakes missed by the local permanent network that doubled the number of aftershocks. The relocated aftershocks are distributed mainly north of the DAS array, and the ground-motion pattern changes also hint small-scale features. Our successful results demonstrate the feasibility of using DAS and dark fiber for rapid postearthquake response.

Effect of complex topography on the wavefield recorded by DAS and buried fiber optic cable at Azuma volcano, Northeast Japan

2020 ◽  
Author(s):  
Kentaro Emoto ◽  
Takeshi Nishimura ◽  
Hisashi Nakahara ◽  
Satoshi Miura ◽  
Mare Yamamoto ◽  
...  
Keyword(s):  
Seismic Waves ◽  
Fiber Optic ◽  
Velocity Structure ◽  
Incident Angle ◽  
Gaussian Function ◽  
Separation Distance ◽  
P Wave ◽  
Small Scale ◽  
Fiber Optic Cable ◽  
Access Road

<p>First DAS observation at Mt. Azuma, Japan was conducted in July 2019 using buried fiber optic cable along the road access to the volcano. Mt. Azuma is an active volcano located in the Tohoku region. Different from non-volcanic regions, wavefields in the volcano is more complex due to its topography and the strong heterogeneities beneath the volcanic edifice. The strength of the scattering of seismic waves due to small-scale velocity heterogeneities in the volcano is reported to be more than one order higher than that in the non-volcanic region. To estimate small-scale heterogeneities, a dense observation network is necessary. The high spatial resolution is one of the advantages of the DAS observation. Therefore, DAS observation in the volcano might be a good chance for the estimation of the small-scale heterogeneity.</p><p> </p><p>We used 14km length of the fiber optic cable buried along to the access road to the observatory near the summit installed by the Ministry of Land, Infrastructure, Transport and Tourism to monitor the volcanic activities. The spatial and temporal samplings were 10m and 1000Hz, respectively. The observation period was for 3 weeks. In addition to regional and teleseismic earthquakes, volcanic earthquakes were also observed. A teleseismic P-wave was analyzed to investigate the effect of small-scale heterogeneities. Because the incident angle of the teleseismic P-wave is almost vertical to the portion of the fiber optic cable used for the DAS observation, a simple model can be used. We calculate the cross-correlation coefficient (CCC) of waveforms between channels and analyze its dependence on the distances between channel pairs. The recorded wavefield was fluctuated by scattering due to the small-scale heterogeneities and different waveforms were recorded even though the propagation distances are the same. Therefore, the spatial variation of the waveforms of teleseismic P-wave recorded at surface stations would be related to the small-scale heterogeneities beneath of the array.</p><p> </p><p>The CCC decreases with increasing separation distance and converges to a constant value. This shape can be modeled by the Gaussian function and we defined the spatial scale of CCC by fitting the Gaussian function. The scale decreases with increasing frequency. The finite difference simulation of the wave propagation was performed by changing the velocity structure and compare the synthetic and observed CCCs. We found that the effect of the topography is most significant on the CCC. Because analyzed waveforms mainly consist of the converted surface wave from the teleseismic P-wave, the effect of subsurface small-scale heterogeneities is not significant. Our result shows that it is necessary to consider the effect of the topography in analyses of DAS data recorded in volcanoes.</p>

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