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Receiver Function Monitoring at Mount St. Helens

Mount St. Helens (MSH) is the most active volcano in the Cascadia volcanic arc. To forecast its future eruptions and understand their driving processes, we need observations spanning the volcanic system. Noise-based seismic interferometry has emerged as a useful tool for monitoring magma transfer and the pressurization state of volcanic systems, but its sensitivity to velocity perturbations decreases rapidly with depth. New methods are needed to monitor deep crustal processes and to detect localized velocity changes, as well as to independently validate the velocity changes measured with the ambient seismic field.

Receiver functions (RFs), a form of event-based seismic interferometry, provide point measurements of the crustal velocity structure beneath a station. With 1500+ magnitude 5.0+ teleseismic earthquakes every year, RFs permit semi-continuous monitoring of the subsurface velocity structure. RFs are body-wave measurements and are uniformly sensitive to velocity perturbations at all depths, complementing the dispersive surface-wave measurements from noise-based seismic interferometry.

We first validate the suitability of RFs for seismic monitoring by characterizing the changes in synthetic RFs that result from velocity perturbations and changes in raypath. We then build a catalog of 27,000+ P and PP phase RFs at MSH using magnitude 5.0+ teleseismic earthquakes from 2009-2020. Considering the seismic monitoring problem within the optimal transport framework, we use the Wasserstein metric and associated transport plan to characterize nonlinear time-warping deformations between full RF ensembles, rather than their stacks. We discuss the possible mechanisms of these waveform variations, including slow-slip events on the nearby Cascadia megathrust, volcanic processes at MSH, and climatological effects.

Presenting Author: Jared T. Bryan

Student Presenter: Yes

Day: 4/22/2021

Time: 5:00 PM - 6:15 PM Pacific

Additional Authors