Seismic detection of increased degassing before Kīlauea's 2008 summit explosion

Abstract

The 2008 explosion that started a new eruption at the summit of Kı %lauea Volcano, Hawaìi, was not preceded by a dramatic increase in earthquakes nor inflation, but was associated with increases in SO 2 emissions and seismic tremor. Here we perform shear wave splitting analysis on local earthquakes spanning the onset of the eruption. Shear wave splitting measures seismic anisotropy and is traditionally used to infer changes in crustal stress over time. We show that shear wave splitting may also vary due to changes in volcanic degassing. The orientation of fast shear waves at Kı %lauea is usually controlled by structure, but in 2008 showed changes with increased SO 2 emissions preceding the start of the summit eruption. This interpretation for changing anisotropy is supported by corresponding decreases in V p /V s ratio. Our result demonstrates a novel method for detecting changes in gas flux using seismic observations and provides a new tool for monitoring under-instrumented volcanoes.

A review of retrospective stress-forecasts of earthquakes and eruptions

“…2 plots the durations of the observed variations of SWS time-delays above swarms of small earthquakes before and after three volcanic eruptions (listed in Table 2) where stress-accumulation and stress-relaxation in SWS time-delays have been observed retrospectively. Other observations of changes in SWS before and after volcanic eruptions have been reported (Miller and Savage, 2001;Gerst and Savage, 2004;Keats et al, 2011;Johnson and Poland, 2013;amongst others). Unfortunately, these other observations do not have the consistent source-to-recorder-geometry (within the shear-wave window at the free surface) required for analysis of the stress-accumulation and stress-relaxation as in Figs.…”

Seismic anisotropy and its precursory change before eruptions at Piton de la Fournaise volcano, La Réunion

“…The evolution of ϕ over time suggests either that the crack populations rotate in response to a rapid reorientation of the stress direction when the dike/magma chamber is inflated or that there is a rapid variation in overpressure [ Johnson and Poland , ; Zatsepin and Crampin , ].…”

Three‐dimensional seismic velocity structure of Mauna Loa and Kilauea volcanoes in Hawaii from local seismic tomography

“…This observation is more consistent with the presence of gas instead of partial melt. Johnson and Poland [2013] proposed that increased degassing can explain a decrease in V p ∕V s ratios and variations in shear wave splitting before Kilauea's 2008 summit explosion. Hansen et al [2004] resolved V p , V p ∕V s , and attenuation models in the ERZ of Kilauea by inverting seismic data recorded by temporary and HVO stations.…”