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

Abstract

[1] 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-longperiod 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. Citation: Lyons, J. J., G. P. Waite, M. Ichihara, and J. M. Lees (2012), Tilt prior to explosions and the effect of topography on ultra-long-period seismic records at

Eruptions at Lone Star geyser, Yellowstone National Park, USA: 2. Constraints on subsurface dynamics

“…Because the signals were not observed on the vertical seismometer component, we infer that the ULP signals were generated by ground surface tilt (rotation) rather than horizontal displacements (translation). We extract the corresponding tilt vector from the acceleration signals recorded on the horizontal mass positions of the seismometer by dividing the instrument acceleration by the gravity acceleration g [ Genco and Ripepe , ; Sanderson et al ., ; Maeda and Takeo , ; Lyons et al ., ; Waite et al ., ]. All the observed ULP tilt signals are nearly identical with amplitudes of ~1 μrad in the E‐W direction and 0.3 µrad in the N‐S direction, and durations of ~4 min (Figure a).…”

The 2007 eruptions and caldera collapse of the Piton de la Fournaise volcano (La Réunion Island) from tilt analysis at a single very broadband seismic station

“…The transfer function of the STS‐1 sensor to the ground velocity below f c (1/360 Hz) is approximately proportional to the square of frequency. Thus, the tilt signal τ ( t ) can be determined from a time integral of the output voltage of the seismometer by the following equation [ Aoyama , ; Genco and Ripepe , ; Lyons et al ., ]: where t is the time, S is the seismometer sensitivity, g is the gravitational acceleration, p ( t ) is the output voltage of the seismometer, and w 0 is an angular frequency equivalent to 2π f c . Although the equation includes the contribution of ground acceleration, its effect is regarded as negligible below f c .…”

Viscous plugging can enhance and modulate explosivity of strombolian eruptions

“…These factors introduce additional complexity compared with the unplugged scenario (e.g., Andronico et al, 2008). This complexity might be manifest in the seismo-acoustic signatures of the explosions (e.g., Johnson and Lees, 2000;Lyons et al, 2012), and in the visual character of the explosions. We note, for instance, that recent high-speed videography studies have identified that gas escape during strombolian explosions is typically pulsatory Gaudin et al, 2014), suggesting greater complexity than simple bursting of an overpressured slug.…”