Sub-Hertz seismic and pressure sensing on long-haul submarine cables

Abstract:

State-of-art tsunami warning relies on seismic data to rapidly determine earthquake source parameters and water level measurements to verify or adjust warnings. However, current seismic or tsunami sensor networks are one-sided or sparse, due to the expense of deploying and maintaining instruments in the ocean. Here we report the first seismic and water pressure sensing over a trans-continental fiber optic cable connecting Los Angeles and Valparaíso, Chile, by monitoring the polarization of regular telecommunication signals. We are able to detect with high signal-to-noise moderate-size earthquakes anywhere along the fiber cable, in the frequency band of 10mHz to 5Hz. Although no tsunami was detected during the few months of testing, we recorded clear water pressure signals in the primary microseism band due to the ocean waves from distant storms. Polarization-based fiber sensing demonstrates huge potential in supplement current tsunami warning systems, to provide faster and more robust warnings. The method is also scalable to deploy, without using special equipment or requiring dedicated fibers.