Locating the Precise Sources of High-Frequency Microseisms Using Distributed Acoustic Sensing

Abstract

Although microseisms have been observed for more than 100 years, the precise locations of their excitation sources in the oceans are still elusive. Underwater Distributed Acoustic Sensing (DAS) brings new opportunities to study microseism generation mechanisms. Using DAS data off the coast of Valencia, Spain, and applying a cross-correlation approach, we show that the sources of high-frequency microseisms (0.5–2 Hz) are confined between 7 and 27 km from the shore, where the water depth varies from 25 to 100 m. Over time, we observe that these sources move quickly along narrow areas, sometimes within a few kilometers. Our methodology applied to DAS data allows us to characterize microseisms with a high spatiotemporal resolution, providing a new way of understanding these global and complex seismic phenomena happening in the oceans.Plain Language SummaryMicroseisms are a type of seismic noise that is ubiquitous on Earth and has been studied for over 100 years. However, we still have no way of knowing exactly where it is generated in the ocean. Recent advances in underwater fiber-optic sensing bring a tremendous opportunity to better understand the source mechanism of microseisms. We use seafloor Distributed Acoustic Sensing data to achieve for the first time a precise localization of the noise sources of high-frequency microseisms. We found that the sources of high-frequency microseisms are very narrow, often only a few kilometers. Moreover, the noise source area is constantly changing with the wind direction.Key PointsA fiber-optic cable on the seafloor is used to locate the sources of high-frequency microseisms with an unprecedented precisionThe sources of high-frequency microseisms quickly move within narrow areas of a few kilometersThe constantly changing source locations are most likely related to the ephemeral behaviors of wind