Dynamic deformation of Seguam Island, Aleutian Islands, Alaska, 1993-2000: Implications for magmatic and hydrothermal processes

The most recent volcanic eruption on Seguam Island was detected in December 1992 and lasted until July or August of 1993. A series of radar interferograms, generated from imagery collected by the European Space Agency's ERS‐1 and ERS‐2 satellites, are used here to map the spatial and temporal evolution of the deformation field from June of 1993 to September of 2000. This evolution consists of a coeruptive period of uplift surrounding the eruption; two posteruptive subsidence signals, centered within each of the two calderas on the island, each of which lasted for 4 years after the end of the eruption; and then uplift beneath the caldera on the eastern side of the island and the surrounding region from mid 1999 through the end of the time series in September 2000. The locations and magnitudes of the sources of the deformation are inferred from the interferometric synthetic aperture radar displacement data using an elastic half‐space Earth model with multiple Mogi point sources and a Levenburg‐Marquardt nonlinear inversion technique. This inference reveals that the sources of subsidence are located within the upper 2 km of the Earth's crust, while the sources of uplift are located below 2.5 km. The locations of dilatational sources are consistent with a model of the volcanic system where ascending magma accumulates below a density or structural boundary near 2.5–3 km depth. The subsidence signals are most likely associated with cooling of shallow magmatic bodies emplaced during the 1992–1993 eruption. However, the possibility that they indicate a combination of magma cooling and depressurization of a hydrothermal system cannot be ruled out using the geodetic data alone. Implications for the long‐term evolution of the volcanic edifice are discussed.