Using Dark Fiber and Distributed Acoustic Sensing for Near-Surface Characterization and Broadband Seismic Event Detection

Abstract

We present the first case study demonstrating the use of regional unlit fiber-optic telecommunication infrastructure (dark fiber) and distributed acoustic sensing for broadband seismic monitoring of both near-surface soil properties and earthquake seismology. We recorded 7 months of passive seismic data on a 27 km section of dark fiber stretching from West Sacramento, CA to Woodland, CA, densely sampled at 2 m spacing. This dataset was processed to extract surface wave velocity information using ambient noise interferometry techniques; the resulting V s profiles were used to map both shallow structural profiles and groundwater depth, thus demonstrating that basin-scale variations in hydrological state can be resolved using this technique. The same array was utilized for detection of regional and teleseismic earthquakes and evaluated for long period response using records from the M8.1 Chiapas, Mexico 2017, Sep 8th event. The combination of these two sets of observations conclusively demonstrates that regionally extensive fiber-optic networks can effectively be utilized for a host of geoscience observation tasks at a combination of scale and resolution previously inaccessible. by 9 and 10 ; other examples include using social media proxies as sensors (e.g. 11 ) or MEMS accelerometers in pervasive stationary devices such as personal computers ( 12 ). Broader efforts to leverage networking and sensor technologies related to the Internet-of-Things (IoT) for seismology are developing but still in their infancy (e.g. 13 ).An alternative approach is to exploit components of the built environment to serve as distributed sensor networks. In this case we explore the use of unlit subsurface fiber-optic cables, commonly referred to as "dark fiber", and distributed acoustic sensing (DAS) to provide such a spatially extensive sensing platform. The vast majority of fiber-optic cables in the earth's near-surface were installed exclusively for the purpose of telecommunications. Due to high cost of fiber-optic installation, typical commercial practice is to deploy significantly more capacity, as measured by fiber count, than required; this practice, combined with advances in bandwidth available per fiber, have yielded a surplus of available fibers that remain unused. The US footprint of such unused fiber networks is massive with tens of thousands of linear kilometers of long distance fiber-optic cables available for lease or purchase in the current environment. One notable aspect of such dark fiber network components is that they tend to utilize existing "right-of-way" corridors along roads and rail connections ( 14 ), environments rich in ambient noise. Given the ubiquitous nature of installed telecom fibers, few studies have explored use of this resource for sensing applications. A single experiment explored the use of Brillouin Optical Time Domain Analysis (BOTDA) to monitor temperature over previously installed telecom fiber ( 15 ); however, these studies were conducted primarily to provide network integrity information rather...

Characterizing Thunder‐Induced Ground Motions Using Fiber‐Optic Distributed Acoustic Sensing Array

“…Recent development of the DAS interrogator technology enables us to convert the telecommunication fiber‐optic cables to an array of acoustic sensors that provides continuous measurements of dynamic strain fields in space and time. The feasibility of DAS arrays for recording ground vibrations has been demonstrated in active‐source seismic surveys (Daley et al, ; Mateeva et al, ), ambient noise monitoring (Dou et al, ; Martin et al, ; Zeng et al, ), and earthquake detection (Ajo‐Franklin et al, ; Lindsey et al, ; Wang et al, ; Yu et al, ). Compared to seismometers, the DAS array is composed of up to tens of kilometers of fiber‐optic cable and is transformed into thousands of virtual sensors with spatial sampling along the cable on the scale of meters.…”

“…Moreover, recent studies demonstrate that telecommunication optical‐fiber cable networks widely installed in recent decades can be used for DAS recording (Jousset et al, ; Martin et al, ). Both Ajo‐Franklin et al () and Yu et al () demonstrated the value of a 20‐km‐long DAS array using telecommunication fiber optics for recording ambient noise and earthquakes in California. Thus, if thunder‐induced seismic waves can be detected by the DAS fiber‐optic array, the high‐fidelity DAS data would be able to provide the detailed characterization of thunder‐induced ground motions in a local area.…”

Spatiotemporal event detection: a review

“…More recently, wireless sensor networks (WSN) and the Internet of Things (IoT) have provided new opportunities for real time and high-resolution monitoring in a distributed network. The (Werner-Allen et al 2006), spatially and temporally continuous air quality monitoring (Boubrima, Bechkit, and Rivano 2017), and earthquake detection from a distributed acoustic sensor network on regional fiber-optic telecommunication infrastructure (Ajo-Franklin et al 2019). Compared to the WSN, an IoT system refers to a large collection of sensors used to individually gather and send data through a router to the Internet.…”

Urban Near-surface Seismic Monitoring using Distributed Acoustic Sensing

“…Over the past decade, DAS has been a rapidly evolving technology for downhole recording in oil and gas reservoirs (Willis et al, 2016). Recent success of DAS applications using existing telecommunication infrastructures (Jousset et al, 2018;Yu et al, 2019;Ajo-Franklin et al, 2019) demonstrates its cost-effectiveness -2-manuscript submitted to Geophysical Research Letters in deployment and maintenance. However, these experiments are conducted for applications in earthquake seismology in remote areas where anthropogenic noise is rare and desired signals are clearly visible above the random noise in DAS measurements.…”