Optical polarization–based seismic and water wave sensing on transoceanic cables

Waiting for earthquakes to call Instrumenting the vast ocean floor is difficult and expensive but important for monitoring earthquakes and tsunamis. Zhan et al. used the polarization of regular telecommunication traffic to detect earthquakes and water swells in a 10,000-kilometer-long fiber-optic submarine cable (see the Perspective by Wilcock). The deep-water Curie cable is not as noisy as terrestrial counterparts, allowing the authors to detect strain from the cable. Results from the 9-month observation period showed how current submarine fiber-optic cables can also be used as a geophysical tool. Science, this issue p. 931; see also p. 882 Tracking polarization of regular telecommunication traffic can detect seismic and water waves along a 10,000-km submarine cable. Seafloor geophysical instrumentation is challenging to deploy and maintain but critical for studying submarine earthquakes and Earth’s interior. Emerging fiber-optic sensing technologies that can leverage submarine telecommunication cables present an opportunity to fill the data gap. We successfully sensed seismic and water waves over a 10,000-kilometer-long submarine cable connecting Los Angeles, California, and Valparaiso, Chile, by monitoring the polarization of regular optical telecommunication channels. We detected multiple moderate-to-large earthquakes along the cable in the 10-millihertz to 5-hertz band. We also recorded pressure signals from ocean swells in the primary microseism band, implying the potential for tsunami sensing. Our method, because it does not require specialized equipment, laser sources, or dedicated fibers, is highly scalable for converting global submarine cables into continuous real-time earthquake and tsunami observatories.