Seeing in the dark: Revealing the subsurface using Fibreoptic Seismic Sensing

Project Highlights:

  • Cutting-edge research revealing the UK subsurface (and changes therein) with unprecedented resolution in time and space.
  • Use of state-of-the-art geophysical equipment and data
  • Development of a research programme with immediate engineering and economic implications

Summary

Seismic waves contain information about both the sources of seismic energy (earthquakes, roads, cities, ocean waves, wind, etc) and the structure and properties of the Earth. By studying seismic waves recorded by dense arrays of sensors, we can construct 3D images of the subsurface. Monitoring changes over time allow to observe and interpret Earth processes that change the subsurface. This is important both for natural hazard assessment (e.g. volcanic monitoring), monitoring effects of climate-change (e.g. glacial melting), or monitoring of subsurface-related industrial activity such as geothermal energy production and waste storage.

Seismic stations often rely inertial sensors to observe seismic waves as they vibrate the earth as the wave travels by. Inertial sensors consist of proof mass suspended within a frame. Measurements of the relative movement between the frame and proof mass senses earth vibrations.

The coverage of conventional seismic stations is usually relatively low. This limits the resolution of structure that can be observed in 3D  and also limits our ability to measure small earthquakes and to attribute them in terms of natural seismicity or industrial activity. Novel geophysical instrumentation allows to measure seismic vibrations using fibreoptic cables. Fibreoptic cables are temporarily deformed as seismic wave pass by. Such deformations can be measured by the backscattering of light that was transmitted into the cable. Fibreoptic geophysical sensor technologies (e.g., Distributed Acoustic Sensing – DAS) has the capability to measure seismic vibrations along 10s of km of fibreoptic cable simultaneously. Fibreoptic sensing could be conducted using existing fibreoptic cables. For example, there are communication lines installed through cities and countryside throughout the UK (ca. 20,000km along railway lines alone). Alternatively, special purpose cables could be installed (semi)-permanently in a pre-designed array.

The University of Leeds has its own instrumentation to conduct fibreoptic sensing. During this project, you will operate this instrumentation and explore the opportunity to develop a UK seismic array based on existing dark fibreoptic cables. You will have the opportunity to employ our own cables in experiments, and take the lead in developing measurement opportunities using existing fibreoptic cables (e.g. those used for communication buried along railway lines). The student will be given free reign and full support in developing and pursuing their own interests in cutting-edge fibreoptic seismological science. Example applications include volcanic monitoring, near-surface rail-road track bed imaging, geothermal energy production, seafloor seismology, etc.

Aims and objectives

During this project, you will develop geophysical methodologies to extract seismic signals from fibreoptic sensing measurements. Objectives that may be explored as part of the project:

  1. Establish the range, scale, and accuracy of subsurface properties that can be inferred from fibreoptic measurements using ambient seismic noise.
  2. Analysis of ground properties, their spatial variability, and temporal fluctuations.
  3. Correlation of the results with measurements made by conventional seismic stations.

 

Training

The student will work principally under the supervision of Dr Sjoerd de Ridder (School of Earth and Environment), an expert in seismic imaging and inversion. Co-supervisors include Dr Adam Booth and Dr Andy Nowacki, who are experts in near-field geophysical testing methods, observational seismology, software development, and geophysical inversion. The student will benefit from access, and the relevant training, to Leeds sector-leading supply of seismic survey equipment:

The project provides specific training in:

  1. Using Distributed Acoustic Sensing equipment for seismic imaging and inversion methods.
  2. Developing theory suitable to process and interpret new types of geophysical datasets.
  3. Integration of learning from synthetic and real-data observations to determine the reliability of engineering-relevant parameters.
  4. The use of cutting-edge laboratory test apparatus to simulate an engineering track settlement.

Research at Leeds

The PhD student will work with experts in this field of research and will be part of the Applied Geophysics research group of the Institute of Applied Geosciences (School of Earth and Environment) of the University of Leeds: The UK’s largest industry facing geoscience institute with application and impact towards energy, environmental, industrial and infrastructural problems. We have a diverse research base, strong international profile and are highly multi-disciplinary, with access to a recent (2019) state of the art high performance computing facility at Leeds; and a suite of fibreoptic sensing instruments (2021). The PhD student will benefit from working within a supportive research group as well as from training at the university. The PhD student will be able to attend national and international conferences and workshops.

Applicant Profile

You will have a strong numeric background (e.g. geophysics, physics, computer sciences, engineering). You should have a passion for new geophysical theory and methods to push the boundaries of subsurface investigation to benefit the engineering sector and its environmental/economic implications. You will be expected to perform both physical laboratory testing and numerical simulation during the project. A competence with programming languages (e.g., Matlab, Python, etc) is also desirable. Finally, with the global reach of this research, you will be encouraged to present at international conferences.

References & Further Reading

Ajo-Franklin, J.B., Dou, S., Lindsey, N.J. et al. Distributed Acoustic Sensing Using Dark Fiber for Near-Surface Characterization and Broadband Seismic Event Detection. Sci Rep 9, 1328 (2019).

BBC News (2019), Leeds & West Yorkshire, Leeds high speed rail research hub backed by government, https://www.bbc.co.uk/news/uk-england-leeds-48938252/, published 10 July 2019, (last accessed 1 November 2019).

Chang, J.P., S.A.L. de Ridder, B.L. Biondi (2016). High-frequency Rayleigh-wave tomography using traffic noise from Long Beach, CA., Geophysics, Vol. 81(2), pp. 1-11.

Killingbeck, S. F., Livermore, P. W., Booth, A. D., & West, L. J. (2018). Multimodal layered transdimensional inversion of seismic dispersion curves with depth constraints. Geochemistry, Geophysics, Geosystems, 19(12), 4957-4971.

de Ridder, S.A.L., B.L. Biondi (2015). Near-Surface Scholte-Wave Velocities at Ekofisk from ShortNoise Recordings by Seismic Noise Gradiometry, Geophysical Research Letters, Vol. 42(17), pp. 7031-7038.