Characterizing Thunder-Induced Ground Motions Using Fiber-Optic Distributed Acoustic Sensing Array

We report for the first time on a distributed acoustic sensing (DAS) array using preexisting underground fiber optics beneath the Penn State campus for detecting and characterizing thunder-induced ground motions. During a half-hour interval from 03:20-03:50 UTC on 15 April 2019 in State College, PA, we identify 18 thunder-induced seismic events in the DAS array data. The high-fidelity DAS data show that the thunder-induced seismics are very broadband, with their peak frequency ranging from 20 to 130 Hz. We use arrival times of the 18 events to estimate the phase velocity of the near surface, the back azimuth, and location of thunder-seismic sources that are verified with lightning locations from the National Lightning Detection Network. Furthermore, the dense DAS data enable us to simulate thunder-seismic wave propagation and full waveform synthetics and further locate the thunder-seismic source by time-reversal migration. Interestingly, we found that thunder-seismic power recorded by DAS is positively correlated with National Lightning Detection Network lightning current power. These findings suggest that fiber-optic DAS observations may offer a new avenue of studying thunder-induced seismics, characterizing the near-surface velocity structure, and probing the thunder-ground coupling process. Plain Language Summary Detailed understanding of how weather processes in the atmosphere couple into seismic waves in the solid Earth is extremely important and will require a high-resolution observation of this coupling in the temporal and spatial scales. This study is the first to demonstrate the use of preexisting telecommunication fiber optics beneath the Penn State campus to characterize thunder-induced seismic waves in the near surface. The fiber-optic array is composed of up to tens of kilometers of fiber-optic cable and can achieve the high resolution at the scale of meters. The high-fidelity distributed acoustic sensing (DAS) data can provide a detailed characterization of thunder-induced signals and further track thunder-induced sources. Moreover, this is the first study to demonstrate the relationship between thunder current energy and DAS recorded ground motion power, suggesting the DAS observations can be useful for characterizing thunder-ground motions and probing the complex thunder-ground coupling process.