Berkeley Lab researchers have turned parts of a 13,000-mile-long testbed of “dark fiber,” unused fiber-optic cable, into a highly sensitive seismic activity sensor that could potentially augment the performance of earthquake early warning systems being developed in the western United States. https://newscenter.lbl.gov/2019/02/05/dark-fiber-lays-groundwork-for-long-distance-earthquake-detection-and-groundwater-mapping/