Tilt prior to explosions and the effect of topography on ultra‐long‐period seismic records at Fuego volcano, Guatemala

Abstract

Ground tilt is measured from broadband seismic records prior to frequent explosions at Fuego volcano, Guatemala. We are able to resolve tilt beginning 20–30 minutes prior to explosions, followed by a rapid reversal in deformation coincident with explosion onsets. The tilt amplitude and polarity recorded on the horizontal channels vary from station to station such that the steep and unusual topography of the upper cone of Fuego appears to affect the ultra‐long‐period signals. We account for the effect of topography and attempt to constrain the tilt source depth and geometry through finite‐difference modeling. The results indicate a shallow spherical pressure source, and that topography must be considered when attempting to model tilt sources at volcanoes with steep topography. The tilt signals are interpreted as pressurization of the shallow conduit beneath a crystallized plug followed by elastic deflation concurrent with explosive pressure release.