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Abstract

Seguam Island is a volcanic centre located within the central Aleutian arc, Alaska, comprising two remnant Quaternary calderas and several post-caldera cones. Pyre Peak, an active stratovolcano that rises above the rim of Seguam’s western caldera, is the primary site of modern volcanic activity and most recently erupted in 1993. There is no geodetic or seismic instrumentation on Seguam Island, so recognising phenomena associated with volcanic unrest is reliant on remote sensing methods such as Interferometric Synthetic Aperture Radar (InSAR). Newly processed InSAR data, acquired by Sentinel-1 between October 2016 and October 2022, reveals continuous subsidence near Pyre Peak, at a rate of ~1 cm/yr, and ~4 cm of uplift within the eastern caldera. We employ the Ensemble Kalman Filter (EnKF), adapted for analyses of volcanic deformation, to determine the best-fit parameters of the deforming magmatic system by sequentially assimilating and inverting the InSAR observations. This workflow is coupled with the Finite Element Method (FEM) to provide the necessary flexibility to explore the observed uplift and subsidence signals. We construct gravitationally loaded models with a full 3D geometry, including the topography of Seguam Island and surrounding ocean bathymetry. Initial results indicate that the deforming subvolcanic system beneath Seguam Island comprises two contrasting components (i.e., deep inflationary and shallow deflationary sources), although the interplay between them is unclear. We investigate the mechanical stability of the system by evaluating stress-based failure criteria throughout the crustal domain, and consider the implications for the future evolution of the magmatic system underlying Seguam Island.