Seismo-acoustic characterisation of the 2018 Ambae (Manaro Voui) eruption, Vanuatu

Abstract

A new episode of unrest and phreatic/phreatomagmatic/magmatic eruptions occurred at Ambae volcano, Vanuatu, in 2017–2018. We installed a multi-station seismo-acoustic network consisting of seven 3-component broadband seismic stations and four 3-element (26–62 m maximum inter-element separation) infrasound arrays during the last phase of the 2018 eruption episode, capturing at least six reported major explosions towards the end of the eruption episode. The observed volcanic seismic signals are generally in the passband 0.5–10 Hz during the eruptive activity, but the corresponding acoustic signals have relatively low frequencies (< 1 Hz). Apparent very-long-period (< 0.2 Hz) seismic signals are also observed during the eruptive episode, but we show that they are generated as ground-coupled airwaves and propagate with atmospheric acoustic velocity. We observe strongly coherent infrasound waves at all acoustic arrays during the eruptions. Using waveform similarity of the acoustic signals, we detect previously unreported volcanic explosions at the summit vent region based on constant-celerity reverse-time-migration (RTM) analysis. The detected acoustic bursts are temporally related to shallow seismic volcanic tremor (frequency content of 5–10 Hz), which we characterise using a simplified amplitude ratio method at a seismic station pair with different distances from the vent. The amplitude ratio increased at the onset of large explosions and then decreased, which is interpreted as the seismic source ascent and descent. The ratio change is potentially useful to recognise volcanic unrest using only two seismic stations quickly. This study reiterates the value of joint seismo-acoustic data for improving interpretation of volcanic activity and reducing ambiguity in geophysical monitoring.

Experimental Multiblast Craters and Ejecta—Seismo‐Acoustics, Jet Characteristics, Craters, and Ejecta Deposits and Implications for Volcanic Explosions

“…In these previous experiments explosive charges were detonated separately, and the effects of each single detonation on the surface morphology and ejected material were studied before detonating the next charge. Although that approach is relevant to many volcanic settings, observation shows that during explosive eruptions many explosions can occur closely spaced in time (Matoza et al., 2014; Park et al., 2021) or simultaneously, superposing their tephra jets, to create one single cumulative eruption column (Dürig, Gudmundsson, & Dellino, 2015). Our study tests whether the results of previous experiments with separate blasts can be extended to those with blasts in rapid succession and with lateral and vertical migration.…”

Experimental multiblast craters and ejecta - seismo-acoustics, jet characteristics, craters, and ejecta deposits and implications for volcanic explosions

“…In these previous experiments explosive charges were detonated separately, and the effects of each single detonation on the surface morphology and ejected material were studied before detonating the next charge. While the approach is relevant to many volcanic settings, observation shows that during explosive eruptions many explosions can occur closely spaced in time (Matoza et al, 2014;Park et al, 2021) or simultaneously, superposing their tephra jets, to create one single cumulative eruption column . Our study tests whether the results of previous experiments with separate blasts can be extended to those with blasts in rapid succession and with lateral and vertical migration.…”

Long-duration seismicity and their relation to Copahue volcano unrest

“…Once the tremor is detected, several methods, such as the amplitude distribution, can be used for location (Ichihara and Matsumoto 2017), whereas analyzing the associated wavefield provides insights into their source mechanism. However, applying these methods requires several stations deployed around the volcano, which may be difficult in remote areas (Jiménez Morales et al 2017;Naismith et al 2019;Park et al 2021) and expensive in low-income countries (Ayele et al 2007;Goitom et al 2015;Barrière et al 2019).…”