Fiber-optic cables are designed to transmit digital data like phone conversations and streaming video, but they also pick up mechanical vibrations from their surroundings. Thus, unused buried optical fibers in telecommunications networks can be repurposed into large-area seismic sensors.
Distributed acoustic sensing (DAS) records seismic waves along fiber-optic cables by analyzing local variations of the backscattered light from successive laser pulses. The rapidly increasing interest in DAS arises from its potential to form arrays that are kilometers in length while providing spatial resolutions on the order of meters and frequency response from millihertz to kilohertz, a combination that can require managing terabytes of data every day.
Last December, a workshop at AGU’s Fall Meeting 2018 was an opportunity to assess the current state of DAS technology and its applications. This 1-day workshop, cosponsored by AGU’s Seismology, Hydrology, and Near-Surface Geophysics sections, brought together 50 participants, including 11 students, who represented DAS technology companies, universities, national laboratories, federal agencies (the Department of Energy (DOE) and the National Science Foundation (NSF)), and NSF facilities (the Incorporated Research Institutions for Seismology and the Center for Transformative Environmental Monitoring Programs). The workshop agenda, attendee list, and many presentations are available at go.wisc.edu/agu_das_workshop.
The workshop alternated between short presentations and breakout sessions. Presentations included the following topics:
- improvements in sensitivity through cable design and instrumentation advances
- the use of existing telecommunications infrastructure
- sensitivity to small displacements at low frequency
- monitoring traffic and industrial facilities
- imaging the near surface using ambient noise
- vertical seismic profiling
- earthquake seismology
- monitoring carbon sequestration and geothermal reservoirs
Breakout sessions, which were divided between “instrumentation” and “applications,” encouraged lively conversations. Topics included machine learning, novel applications, comparisons of DAS with conventional seismometers, and data management.
The day concluded with a committee-of-the-whole discussion about the potential of facilitating communication among DAS researchers within the AGU community through an NSF Research Coordination Network (RCN). Special sessions at AGU, the Society of Exploration Geophysicists, and the European Geosciences Union meetings within the past year or planned in the near future reflect the timeliness of this topic. An AGU monograph on DAS is currently in progress.
An RCN could facilitate research opportunities. For example, one workshop presentation described plans for a 50-ton chemical blast on 19 December 2018 at the Nevada Test Site. This information provided an opportunity for interested parties to prepare for the event. Another example is DOE’s Frontier Observatory for Research in Geothermal Energy (FORGE) initiative, which will include a DAS cable installed in a deep borehole. Other benefits of an RCN could include the ability to connect with related disciplines such as optoelectronics and machine learning. An RCN could also sponsor regular workshops and short courses and prepare reports for the community and federal agencies.
We thank Matt Becker, Biondo Biondi, and Jonathan Ajo-Franklin for leading breakout sessions and recording notes. Contact Herb Wang ([email protected]) to subscribe to the DAS Interest Group.
—Herbert Wang ([email protected]), Department of Geoscience, University of Wisconsin–Madison; Xavier Comas, Department of Geosciences, Florida Atlantic University, Davie; and Scott Tyler, Department of Geological Sciences and Engineering, University of Nevada, Reno