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The Eastern Caldera Medium-Power Junction Box (MJ03E) supports geophysical instruments in the Eastern side of the 3-km-across caldera at the summit of Axial Seamount, at a water depth of ~1,520 meters. The instruments are designed to measure local seismic events associated with migration of melt and volatiles within the volcano, as well as far-field seismic events. They also measure uplift and deflation of the seafloor associated with ingress of melt within the underlying magma chamber, and collapse of the seafloor during diking-eruptive events. This site was chosen because Axial has erupted in 1988, 2011, and again in 2015. During the 2015 event, over 8,000 earthquakes were measured with the cabled geophysical array, and data were streamed live back to shore in real-time. A 635 meter-long electro-optical cable from Primary Node PN03B provides the junction box with significant power (375 V) and bandwidth (1 Gbs) to operate the instruments and transmit data to shore.
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Geodetic Monitoring at Axial Seamount Since Its 2015 Eruption Reveals a Waning Magma Supply and Tightly Linked Rates of Deformation and Seismicity
Abstract Axial Seamount is a basaltic hot spot volcano with a summit caldera at a depth of ∼1,500 m below sea level, superimposed on the Juan de Fuca spreading ridge, giving it a robust and continuous magma supply. Axial erupted in 1998, 2011, and 2015, and is monitored by a cabled network of instruments including bottom pressure recorders and seismometers. Since its last eruption, Axial has re‐inflated to 85%–90% of its pre‐eruption level. During that time, we have identified eight discrete, short‐term deflation events of 1–4 cm over 1–3 weeks that occurred quasi‐periodically, about every 4–6 months between August 2016 and May 2019. During each short‐term deflation event, the rate of earthquakes dropped abruptly to low levels, and then did not return to higher levels until reinflation had resumed and returned near its previous high. The long‐term geodetic monitoring record suggests that the rate of magma supply has varied by an order of magnitude over decadal time scales. There was a surge in magma supply between 2011 and 2015, causing those two eruptions to be closely spaced in time and the supply rate has been waning since then. This waning supply has implications for eruption forecasting and the next eruption at Axial still appears to be 4–9 years away. We also show that the number of earthquakes per unit of uplift has increased exponentially with total uplift since the 2015 eruption, a pattern consistent with a mechanical model of cumulative rock damage leading to bulk failure during magma accumulation between eruptions.
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- PAR ID:
- 10363467
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Geochemistry, Geophysics, Geosystems
- Volume:
- 23
- Issue:
- 1
- ISSN:
- 1525-2027
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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