Understanding the long-term 4D Dynamics of the Seismic Velocity at Mount St Helens, WA, USA

Mt. St. Helens is an explosively erupting volcano located in close vicinity to major metropolitan centres on the US West Coast. In recent history, Mt. St. Helens (MSH) erupted twice, in 2004 and 1980, causing more than 50 fatalities and over one billion USD of damage. Here, we present a seismic velocity change time series (dv/v) of an unprecedented length covering the years 1998-2023 recovered from seismic ambient noise. We discuss challenges arising from the very heterogeneous nature of the dataset recorded on a variety of seismic stations and discuss methods to address them. To reconcile measurements from different periods, we rely on an approach that simultaneously normalises our measurements and allows us to locate our dv/v estimates in space. Finally, we compare our obtained results to a multitude of auxiliary measurements, including GPS, earthquake, and meteorological data.  By employing models that link dv/v to these mechanisms, we attempt to unravel the contribution of each mechanism to our velocity change estimate. At volcanoes like MSH, our ultimate goal is to reliably isolate the volcanic contribution to dv/v, thereby aiding the identification of potential volcanic precursors.