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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.
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Capturing Seismic Signals From Karst Aquifer Injection Experiments and a Natural Recharge Event
Abstract Variations in subsurface flow processes through a karst aquifer that feeds Bear Spring in southeastern Minnesota were captured on a temporary seismic network during injection experiments and a natural recharge event. Each experiment involved injecting ∼13,000 L of water into an overflow spring, and the natural event was triggered by a large rainstorm of ∼70 min in duration. During the injection experiments, the largest amplitude signals in the ground velocity seismograms occurred as the water first fell onto the rock at the overflow spring and as the large slug of water reached a sump or water‐filled passage. During the natural rainstorm event, the overflow spring began flowing and total spring discharge (perennial emanation points and the overflow spring) increased from ∼100 to 300 L/s. Seismic signals during and following the rain event include broadband noise from raindrops impacting the ground, as well as large amplitude signals while water levels rose; the latter occurred over a 5‐s period, producing multiple pulses of ground motion up to ∼0.5 mm/s. Based on seismic array analysis, high frequency signals during the natural recharge event and one of the injection experiments are largely sourced from south of the array, where a sump exists and the conduit orientation changes, but additional modeling is required to further understand which of a set of possible mechanisms is mostly likely the cause of these seismic signals.
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- Award ID(s):
- 1850667
- PAR ID:
- 10409473
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Solid Earth
- Volume:
- 128
- Issue:
- 4
- ISSN:
- 2169-9313
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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