ER-PF: Using Distributed Acoustic Sensing for Tremor Detection and Site Characterization in Cascadia to Evaluate Earthquake Hazard

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This award is funded in whole or in part under the American Rescue Plan Act of 2021 (Public Law 117-2).Dr. Manuel Mendoza has been granted an EAR Postdoctoral Fellowship to carry out research and education plans at University of Colorado Boulder and Colorado School of Mines. Dr. Mendoza plans to develop a new technique for earthquake monitoring called distributed acoustic sensing (DAS). DAS uses dark (unlit/unused) existing telecommunication fiber optic cables and turns them into an instrument that acts as a network capable of detecting tiny or distant seismic (earthquake) events. In the Pacific Northwest of the US where two tectonic plates converge, the conditions are right for large earthquakes which could result in other hazards such as tsunamis. Therefore, large-scale and continuous seismic monitoring is needed to evaluate the impending risks. In this project, Dr. Mendoza will work alongside Professors Anne Sheehan and Dr. Ge Jin to test and demonstrate DAS performance capabilities by carrying out a DAS experiment in Northwestern Washington. Specifically, the work will investigate seismic events known as “tremor” and determine how local geologic conditions vary along the fiber cable. Dr. Mendoza’s work will advance understanding of earthquakes, how the ground shakes in response to them, and consequent seismic hazards. The proposed study will provide opportunities for DAS to be applied at larger scales alongside existing seismic networks to perform multi and interdisciplinary research and monitoring of Earth processes. The project will also allow Dr. Mendoza to teach and mentor students from underrepresented groups, including as a mentor on the Diversity, Inclusion, and Access committee at the Colorado School of Mines and as a summer internship mentor at University of Colorado Boulder. Other activities associated with this project include designing and leading a local DAS experiment for a geophysics course and supervising the professional and educational development of an undergraduate student who will conduct original research with the DAS data. At both campuses, the PI will engage in outreach activities aimed at increasing public scientific literacy and broadening participation in the S.T.E.M fields.Distributed acoustic sensing (DAS) using fiber-optics to measure deformation (strain) caused by seismic perturbations in the Earth has, in recent years, proved to be a highly applicable and promising tool in seismology. This is owed to its ability to be configured as a seismic array with an aperture on the order of tens of kilometers, meter-level sensor (i.e. channel) spacing, and performance comparable to that of conventional broadband seismometers. This implies that DAS arrays can blanket a large area while not suffering from spatial aliasing when sampling the seismic wavefield – unlike traditional networks – and provide new information in high fidelity that often goes missed. A single DAS experiment can therefore be used to simultaneously investigate a variety of Earth processes occurring across different spatial and temporal scales. Here, the investigators will conduct the first known DAS experiment in Cascadia using fiber from an existing telecommunication cable, to monitor tremor and characterize site conditions for the purpose of evaluating seismic hazard. Specifically, the PI will pursue three primary scientific goals: (1) Use DAS to detect and locate tremor in Cascadia; (2) characterize its spatiotemporal behavior and infer its contribution to stressing the up-dip locked portion of the plate interface; and (3) determine meter-level variation in site conditions along the DAS array. These goals will be addressed by employing seismic array-based techniques such as beamforming and beam back-projection to capture tremor, as well as ambient noise interferometry techniques to estimate shear wave velocities of the top 30 meters (Vs30). The results obtained from this study will be compared to other observations performed using different instruments and methods, to demonstrate the efficacy of DAS in improving earthquake and ground shaking models in Cascadia and assess its implications for future experiments in a variety of tectonic settings.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.