Towards multi-method geophysical sensing on submarine cables

The oceans present a major gap in geophysical instrumentation, hindering fundamental research on submarine earthquakes and the Earth&#8217;s interior structure, as well as effective earthquake and tsunami warning for offshore events. Emerging fiber-optic sensing technologies that can leverage submarine telecommunication cables present an new opportunity in filling the data gap. Marra et al. (2018) turned a 96 km long submarine cable into a sensitive seismic sensor using ultra-stable laser interferometry of a round-tripped signal. Another technology, Distributed Acoustic Sensing (DAS), interrogates intrinsic Rayleigh backscattering and converts tens of kilometers of dedicated fiber into thousands of seismic strainmeters on the seafloor (e.g., Lindsey et al., 2019; Sladen et al., 2019; Williams et al., 2019; Spica et al., 2020). Zhan et al. (2021) successfully sensed seismic and water waves over a 10,000 km long submarine cable connecting Los Angeles and Valparaiso, by monitoring the polarization of regular optical telecommunication channels. However, these new technologies have substantially different levels of sensitivity, coverage, spatial resolution, and scalability. In this talk, we advocate that strategic combinations of the different sensing techniques (including conventional geophysical networks) are necessary to provide the broadest coverage of the seafloor while making high-fidelity, physically interpretable measurements. Strategic collaborations between the geophysics community and telecommunication community without burdening the telecomm operation (e.g., by multiplexing or using regular telecom signals) will be critical to the long term success.&#160;Marra, G., C. Clivati, R. Luckett, A. Tampellini, J. Kronj&#228;ger, L. Wright, A. Mura, F. Levi, S. Robinson, A. Xuereb, B. Baptie, D. Calonico, 2018. Ultrastable laser interferometry for earthquake detection with terrestrial and submarine cables. Science, eaat4458.Lindsey, N.J., T. C. Dawe, J. B. Ajo-Franklin, 2019. Illuminating seafloor faults and ocean dynamics with dark fiber distributed acoustic sensing. Science. 366, 1103&#8211;1107.Sladen, A., D. Rivet, J. P. Ampuero, L. De Barros, Y. Hello, G. Calbris, P. Lamare, 2019. Distributed sensing of earthquakes and ocean-solid Earth interactions on seafloor telecom cables. Nat Commun. 10, 5777.Spica, Z.J., Nishida, K., Akuhara, T., P&#233;tr&#233;lis, F., Shinohara, M. and Yamada, T., 2020. Marine Sediment Characterized by Ocean&#8208;Bottom Fiber&#8208;Optic Seismology. Geophysical Research Letters, 47(16), p.e2020GL088360.Williams, E.F., M. R. Fern&#225;ndez-Ruiz, R. Magalhaes, R. Vanthillo, Z. Zhan, M. Gonz&#225;lez-Herr&#225;ez, H. F. Martins, 2019. Distributed sensing of microseisms and teleseisms with submarine dark fibers. Nat Commun. 10, 5778.Zhan, Z., M. Cantono, V. Kamalov, A. Mecozzi, R. Muller, S. Yin, J.C. Castellanos, 2021. Optical polarization-based seismic and water wave sensing on transoceanic cables. Science, in press.

Download Full-text

Optical fiber as distributed acoustic sensing element with improved Rayleigh backscattering sensitivity and robustness under elevated temperature

Optical Fibers and Sensors for Medical Diagnostics, Treatment and Environmental Applications XXI ◽

10.1117/12.2581775 ◽

2021 ◽

Author(s):

Hongchao Wu ◽

Andrei Stolov ◽

Kenneth Feder

Keyword(s):

Elevated Temperature ◽

Optical Fiber ◽

Sensing Element ◽

Acoustic Sensing ◽

Rayleigh Backscattering ◽

Distributed Acoustic Sensing

Download Full-text

Near-field spectral analysis of data-integrative dynamic rupture earthquake simulations of the 1992 Landers earthquake

10.5194/egusphere-egu2020-22673 ◽

2020 ◽

Author(s):

Nico Schliwa ◽

Alice-Agnes Gabriel

Keyword(s):

Spectral Analysis ◽

Ground Motion ◽

Near Field ◽

Slip Distribution ◽

Corner Frequency ◽

Dynamic Rupture ◽

Geophysical Research ◽

Acoustic Sensing ◽

Distributed Acoustic Sensing ◽

Large Earthquakes

The rise of observations from Distributed Acoustic Sensing (e.g., Zhan 2020) and high-rate GNSS networks (e.g., Madariaga et al., 2019) highlight the potential of dense ground motion observations in the near-field of large earthquakes. Here, spectral analysis of >100,000 synthetic near-field strong motion waveforms (up to 2 Hz) is presented in terms of directivity, corner frequency, fall-off rate, moment estimates and static displacements.The waveforms are generated in 3&#8208;D large-scale dynamic rupture simulations which incorporate the interplay of complex fault geometry, topography, 3&#8208;D rheology and viscoelastic attenuation (Wollherr et al., 2019). A preferred scenario accounts for off-fault deformation and reproduces a broad range of observations, including final slip distribution, shallow slip deficits, and spontaneous rupture termination and transfers between fault segments. We examine the effects of variations in modeling parameterization within a suite of scenarios including purely elastic setups and models neglecting viscoelastic attenuation.&#160;First, near-field corner frequency mapping implementing a novel spectral seismological misfit criterion reveals rays of elevated corner frequencies radiating from each slipping fault at 45 degree to rupture forward direction. The azimuthal spectral variations are specifically dominant in the vertical components indicating we map rays of direct P-waves prevailing (Hanks, 1980). The spatial variation in corner frequencies carries information on co-seismic fault segmentation, slip distribution, focal mechanisms and stress drop. Second, spectral fall-off rates are variably inferred during picking the associated corner frequencies to identify the crossover from near-field to far-field spectral behaviour in dependence on distance and azimuth. Third, we determine static displacements with the help of near-field seismic spectra.Our findings highlight the future potential of spectral analysis of spatially dense (low frequency) ground motion observations for inferring earthquake kinematics and understanding earthquake physics directly from near-field data; while synthetic studies are crucial to identify "what to look for" in the vast amount of data generated.References:Hanks, T.C., 1980. The corner frequency shift, earthquake source models and Q.Madariaga, R., Ruiz, S., Rivera, E., Leyton, F. and Baez, J.C., 2019. Near-field spectra of large earthquakes. Pure and Applied Geophysics, 176(3), pp.983-1001.Wollherr, S., Gabriel, A.-A. and Mai, P.M., 2019.&#160; Landers 1992 &#8220;reloaded&#8221;: Integrative dynamic earthquake rupture modeling. Journal of Geophysical Research: Solid Earth, 124(7), pp.6666-6702.Zhan, Z., 2020. Distributed Acoustic Sensing Turns Fiber&#8208;Optic Cables into Sensitive Seismic Antennas. Seismological Research Letters, 91(1), pp.1-15.

Download Full-text

Recent Advances in Distributed Acoustic Sensing Based on Phase-Sensitive Optical Time Domain Reflectometry

Journal of Sensors ◽

10.1155/2018/3897873 ◽

2018 ◽

Vol 2018 ◽

pp. 1-16 ◽

Cited By ~ 37

Author(s):

Yonas Muanenda

Keyword(s):

Time Domain ◽

Time Domain Reflectometry ◽

Fiber Optic Sensor ◽

Acoustic Sensing ◽

Rayleigh Backscattering ◽

Recent Advances ◽

Optical Time Domain Reflectometry ◽

Phase Sensitive ◽

Distributed Acoustic Sensing ◽

Optical Time

Distributed acoustic sensing (DAS) using coherent Rayleigh backscattering in an optical fiber has become a ubiquitous technique for monitoring multiple dynamic events in real time. It has continued to constitute a steadily increasing share of the fiber-optic sensor market, thanks to its interesting applications in many safety, security, and integrity monitoring systems. In this contribution, an overview of the recent advances of research in DAS based on phase-sensitive optical time domain reflectometry (ϕ-OTDR) is provided. Some advanced techniques used to enhance the performance of ϕ-OTDR sensors for measuring backscattering intensity changes through reduction of measurement noise are presented, in addition to methods used to increase the dynamic measurement capacity of ϕ-OTDR schemes beyond conventional limits set by the sensing distance. Recent ϕ-OTDR configurations which significantly enhance the measurement spatial resolution, including those which decouple it from the probing pulse width, are also discussed. Finally, a review of recent advances in more precise quantitative measurement of an external impact based on frequency shift and phase demodulation methods using simple direct detection ϕ-OTDR schemes is given.

Download Full-text

Enhanced Optical Fiber for Distributed Acoustic Sensing beyond the Limits of Rayleigh Backscattering

iScience ◽

10.1016/j.isci.2020.101137 ◽

2020 ◽

Vol 23 (6) ◽

pp. 101137 ◽

Cited By ~ 1

Author(s):

Paul S. Westbrook ◽

Kenneth S. Feder ◽

Tristan Kremp ◽

Eric M. Monberg ◽

Hongchao Wu ◽

...

Keyword(s):

Optical Fiber ◽

Acoustic Sensing ◽

Rayleigh Backscattering ◽

Distributed Acoustic Sensing

Download Full-text

Optical polarization–based seismic and water wave sensing on transoceanic cables

Science ◽

10.1126/science.abe6648 ◽

2021 ◽

Vol 371 (6532) ◽

pp. 931-936 ◽

Cited By ~ 2

Author(s):

Zhongwen Zhan ◽

Mattia Cantono ◽

Valey Kamalov ◽

Antonio Mecozzi ◽

Rafael Müller ◽

...

Keyword(s):

Los Angeles ◽

Water Waves ◽

Fiber Optic ◽

Submarine Cable ◽

Submarine Earthquakes ◽

Specialized Equipment ◽

Laser Sources ◽

Data Gap ◽

Submarine Cables ◽

Large Earthquakes

Seafloor geophysical instrumentation is challenging to deploy and maintain but critical for studying submarine earthquakes and Earth’s interior. Emerging fiber-optic sensing technologies that can leverage submarine telecommunication cables present an opportunity to fill the data gap. We successfully sensed seismic and water waves over a 10,000-kilometer-long submarine cable connecting Los Angeles, California, and Valparaiso, Chile, by monitoring the polarization of regular optical telecommunication channels. We detected multiple moderate-to-large earthquakes along the cable in the 10-millihertz to 5-hertz band. We also recorded pressure signals from ocean swells in the primary microseism band, implying the potential for tsunami sensing. Our method, because it does not require specialized equipment, laser sources, or dedicated fibers, is highly scalable for converting global submarine cables into continuous real-time earthquake and tsunami observatories.

Download Full-text

Illuminating seafloor faults and ocean dynamics with dark fiber distributed acoustic sensing

Science ◽

10.1126/science.aay5881 ◽

2019 ◽

Vol 366 (6469) ◽

pp. 1103-1107 ◽

Cited By ~ 23

Author(s):

Nathaniel J. Lindsey ◽

T. Craig Dawe ◽

Jonathan B. Ajo-Franklin

Keyword(s):

Ocean Dynamics ◽

Sea State ◽

Acoustic Sensing ◽

Ocean Surface Waves ◽

Sensing Technology ◽

Northern Pacific ◽

Distributed Acoustic Sensing ◽

A Minor ◽

Array Recordings

Distributed fiber-optic sensing technology coupled to existing subsea cables (dark fiber) allows observation of ocean and solid earth phenomena. We used an optical fiber from the cable supporting the Monterey Accelerated Research System during a 4-day maintenance period with a distributed acoustic sensing (DAS) instrument operating onshore, creating a ~10,000-component, 20-kilometer-long seismic array. Recordings of a minor earthquake wavefield identified multiple submarine fault zones. Ambient noise was dominated by shoaling ocean surface waves but also contained observations of in situ secondary microseism generation, post–low-tide bores, storm-induced sediment transport, infragravity waves, and breaking internal waves. DAS amplitudes in the microseism band tracked sea-state dynamics during a storm cycle in the northern Pacific. These observations highlight this method’s potential for marine geophysics.

Download Full-text