Illuminating Earth's faults

Submarine fiber-optic cables drive discovery of fault locations and ocean dynamics Earthquakes are primarily caused by movement of big land masses—tectonic plates—at large physical fractures in Earth's crust (faults). Furthermore, faults sometimes convey mineral-rich fluids, oil, gas, and hot water and thus contribute to our mineral and energy resources. Unfortunately, scientists do not yet know where all of Earth's faults are located, especially when they reside under cities or the seafloor, where their movement can produce large earthquakes and tsunamis. Without a complete map of Earth's faults, economic opportunities may be overlooked and seismic hazards may be underestimated. On page 1103 of this issue, Lindsey et al. ( 1 ) describe the use of a method—distributed acoustic sensing (DAS)—that makes it possible to discover previously unidentified faults in Monterey Bay, California, the United States.