Inferring eruption dynamics from seismometer-derived ground tilt measurements: a case study of two end-member volcanic systems

Abstract

Modern broadband seismometers are inertial sensors, and are sensitive to ground tilt as a conse­ quence of this design. We use broadband seismometers positioned on Mt. Erebus on Ross Island, Antarctica, and Augustine Volcano in the Lower Cook Inlet, Alaska, to recover tilt measurements during individual volcanic explosions to investigate the magmatic system configuration of each volcano. At Mt. Erebus, thought to be an end-member open conduit volcanic system, we find no evidence of tilting associated with the Strombolian explosions produced by the volcano. Because tilt preceding Strombolian explosions has been observed at other volcanoes, we interpret the lack of tilt at Erebus as evidence that its conduit system lacks any viscous plugging or mechanical re­ strictions that are necessary to generate explosion-related tilt. At Augustine Volcano we are able to measure tilt changes associated with each of the thirteen events during the explosive phase of its 2006 eruption. We use the tilt changes to invert for a dual deformation source model of a depressur­ izing open conduit above a depressurizing prolate spheroid. This deflation source geometry is in agreement with an existing magmatic system model developed with petrologic, seismic, and GPS data, offering further support to the existing model.