New observations of displacement steps associated with volcano seismic long‐period events, constrained by step table experiments

Abstract

Long‐period (LP) volcano seismic events often precede volcanic eruptions and are viewed with considerable interest in hazard assessment. They are usually thought to be associated with resonating fluid‐filled conduits although alternative models involving material failure have recently been proposed. Through recent field experiments, we uncovered a step‐like displacement component associated with some LP events, outside the spectral range of the typically narrow‐band analysis for this kind of event. Bespoke laboratory experiments with step tables show that steps of the order of a few micrometers can be extracted from seismograms, where long‐period noise is estimated and removed with moving median filters. Using these constraints, we observe step‐like ground deformation in LP recordings near the summits of Turrialba and Etna Volcanoes. This represents a previously unobserved static component in the source time history of LP events, with implications for the underlying source process.

Relocation of long‐period (LP) seismic events reveals en echelon fractures in the upper edifice of Turrialba volcano, Costa Rica

“…The geometry of the tensile cracks found through MTI is superimposed onto the relocated structure, revealing en echelon fractures within Turrialba's edifice. In combination with results from previous studies [Eyre et al, 2015;Thun et al, 2015], we suggest that this structure could be a response to the deformation of the shallow part of the edifice [Bean et al, 2014], with a shearing band together with high fluid pressure inducing tensile fractures at The obtained relocation structure, when combined with the source mechanisms obtained through MTI, reveals a detailed geometrical relationship between LP sources, which can be interpreted with respect to a new, recently proposed brittle deformation-based LP source model. This study therefore highlights the need for further LP event studies to implement a more systematic relocation procedure, together with joint interpretation of the source mechanisms, to better infer the source processes of LP events within volcanoes.…”

“…Similar models have been proposed by, e.g., Jousset et al [2013] on Merapi volcano. However, Thun et al [2015] showed that the LP events used here contain a significant static displacement component. This observation is not consistent with a pure resonance mechanism.…”

Micrometre-scale deformation observations reveal fundamental controls on geological rifting

“…The sources inferred above would theoretically cause total static displacements smaller than 1 µm at the next closest station, DY1. Sub-micrometre steps are not detectable with our instruments and methods14. The fact that the events are not visible at the other stations also implies that the dynamic seismic signals, i.e.…”

“…As high-frequency waves are attenuated strongly when travelling through the ground, such high frequencies thus indicate a fracturing process close to the station. In a recent study14, we presented a new data processing approach that allows for the recovery of micrometre-scale displacement steps from instrument-corrected seismograms. It is based on long-period noise removal using median filters and its performance was confirmed by laboratory experiments.…”

“…( b ) Scalogram illustrating relative frequency content – the main frequency peak lies between 3 Hz and 8 Hz, with an additional peak above 25 Hz. ( c–e ) Vertical, North and East displacements, respectively; processed with the median filter method14. The resulting displacement step is about 17 μm upward and 123 μm in a northwest direction.…”