Seismo Lab Brown Bag Seminar

Distributed Acoustic Sensing (DAS) is an emerging technology that converts optical fibers into dense arrays of strainmeters, significantly enhancing our understanding of earthquake physics and Earth's structure. While most past DAS studies have focused primarily on seismic wave phase information, accurate measurements of true ground motion amplitudes are crucial for comprehensive future analyses. However, amplitudes in DAS recordings, especially for pre-existing telecommunication cables with uncertain fiber-ground coupling, have not been fully quantified. By calibrating three DAS arrays with co-located seismometers, we systematically evaluate DAS amplitudes. Our results indicate that the average DAS amplitude of earthquake signals closely matches that of co-located seismometer data across frequencies from 0.01 to 10 Hz. The noise floor of DAS is comparable to that of strong-motion stations but higher than that of broadband stations. The saturation amplitude of DAS is adjustable by modifying the pulse repetition rate and gauge length. We also demonstrate how our findings enhance the understanding of fiber-optic seismology and its implications for natural hazard mitigation on Earth and future lunar seismology. Specifically, our results suggest that with proper settings, DAS can detect P-waves from an M6+ earthquake occurring 10 km from the cable without saturation, indicating its viability for earthquake early warning. Furthermore, we show that DAS is ideal for addressing the strong scattering challenge in lunar seismology. By comparing Apollo moonquake signals with DAS's current minimum noise floor observed in Antarctica's quiet conditions, we find that existing DAS technology can detect more than 60% of moonquakes previously recorded by Apollo seismic sensors. With expected and achievable improvements in DAS equipment, detection rates could surpass 90%. The deployment of DAS on the Moon could mark a revolutionary step in lunar seismology.

Short Bio: Dr. Qiushi Zhai is a postdoc at seismolab of Caltech, working with Prof. Zhongwen Zhan on fiber-optic distributed acoustic sensing (DAS) technology in earth, environmental, and planetary sciences. He earned his PhD in geophysics from the Georgia Institute of Technology in 2022. Before that, he earned his bachelor's and master's degree in geophysics from the University of Science and Technology of China (USTC) in 2014 and 2017.