Abstract
Abstract. Continuous seismic monitoring of the Earth's near surface (top 100 m), especially with improved resolution and extent of data both in space and time, would yield more accurate insights about the effect of extreme-weather events (e.g., flooding or drought) and climate change on the Earth's surface and subsurface systems. However, continuous long-term seismic monitoring, especially in urban areas, remains challenging. We describe the Fiber Optic foR Environmental SEnsEing (FORESEE) project in Pennsylvania, USA, the first continuous-monitoring distributed acoustic sensing (DAS) fiber array in the eastern USA. This array is made up of nearly 5 km of pre-existing dark telecommunication fiber underneath the Pennsylvania State University campus. A major thrust of this experiment is the study of urban geohazard and hydrological systems through near-surface seismic monitoring. Here we detail the FORESEE experiment deployment and instrument calibration, and describe multiple observations of seismic sources in the first year. We calibrate the array by comparison to earthquake data from a nearby seismometer and to active-source geophone data. We observed a wide variety of seismic signatures in our DAS recordings: natural events (earthquakes and thunderstorms) and anthropogenic events (mining blasts, vehicles, music concerts and walking steps). Preliminary analysis of these signals suggests DAS has the capability to sense broadband vibrations and discriminate between seismic signatures of different quakes and anthropogenic sources. With the success of collecting 1 year of continuous DAS recordings, we conclude that DAS along with telecommunication fiber will potentially serve the purpose of continuous near-surface seismic monitoring in populated areas.
Highlights
As increasingly more people reside in urban areas, and as climate change leads to more extreme weather patterns, we need more reliable data to understand the Earth’s surface and subsurface systems and design appropriate strategies to estimate risks and reduce the vulnerability of people in cities
We have deployed the foR Environmental SEnsEing (FORESEE) array using existing fiber optics under the Penn State University campus in Pennsylvania, USA, and acquired 75 TB of data over the course of about 360 d since 5 April 2019. While this array confirms findings from earlier dark-fiber arrays in the western USA that such a system can record local active seismic sources and earthquakes, this is the first experiment of its kind in the eastern USA and reveals a wider range of new signals, including thunderquakes, concerts and even footsteps
The density of these broadband distributed acoustic sensing (DAS) recordings provides extraordinary resolution that enables insight into their cause and allows us to distinguish between these various signals
Summary
As increasingly more people reside in urban areas, and as climate change leads to more extreme weather patterns, we need more reliable data to understand the Earth’s surface and subsurface systems and design appropriate strategies to estimate risks and reduce the vulnerability of people in cities. Near-surface Earth materials driven by multiscale physical, chemical and biological processes are extremely heterogeneous, varying spatially at the scale of meters or even smaller and temporally from milliseconds (or less) to millions of years. This suggests that dense and continuous measurements that can yield spatiotemporal information are valuable, and such data could be provided by a dense and (semi)permanent deployable seismic array. Despite their expected utility for real-time monitoring of subsurface environmental systems, neither temporary nor permanent dense seismic geophone arrays have been widely deployed in urban areas. The primary limiting factors in deploying traditional seismic monitoring include restrictions on human-controlled sources in densely populated areas, difficulty obtaining permission and space to deploy sensors near civil infrastructure, challenges in securing sensors against theft or vandalism, and high costs to maintain power and data transfer from geophones
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