Mechanics of fault reactivation before, during, and after the 2015 eruption of Axial Seamount

Levy, S.; Bohnenstiehl, D. R.; Sprinkle, Parker; Boettcher, M. S.; Wilcock, William S. D.; Tolstoy, M.; Waldhauser, F.

doi:10.1130/g39978.1

Cited by 33 publications

(70 citation statements)

References 18 publications

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“…This is the case at Axial Seamount where an ~8‐km‐long by ~3‐km‐wide rectangular caldera overlies a shallow, 14‐km‐long magma chamber (MMR) characterized by rough roof topography (Figure ). Similarly, the fault mechanisms resolved by the new hypocentral location estimates are consistent with focal mechanisms (Levy et al, ) and analog experiments (Acocella, ), which find that during an eruption the caldera floor moves rapidly downward as a coherent piston between two outward dipping faults (Figures d and b). Then, continued subsidence of the caldera floor can lead to the formation of inward dipping faults that define the rim of the caldera (Figures e and b).…”

Section: Discussionsupporting

confidence: 85%

“…Additionally, beneath the northern half of the caldera, our revised locations reveal a new set of conjugate inward dipping faults extending from the seafloor to~2.25 km depth and dipping at 40°to 47° ( Figure 8e). These two inward dipping bands of seismicity were absent in previous location estimates (i.e., Levy et al, 2018) and are the result of using a 3-D velocity structure in our relocation algorithm. In along caldera sections, our seismicity distribution beneath the east and west walls of the caldera is spatially complex and differs from the mostly conic distribution observed by (see Figures S1b and S1c).…”

Section: Journal Of Geophysical Research: Solid Earthmentioning

confidence: 65%

“…Additionally, looking at all vertical sections (Figures 8b-8e) we observe that our relocated seismicity is mapped to slightly shallower depths. In across caldera sections, the outward dipping fault zones defined by the seismicity extend from near the seafloor to 3-3.25 km depth and they dip at 42°to 60° (Figure 8d), compared to a maximum Figure S1) and dips of 67°± 4°in Levy et al (2018). Additionally, beneath the northern half of the caldera, our revised locations reveal a new set of conjugate inward dipping faults extending from the seafloor to~2.25 km depth and dipping at 40°to 47° ( Figure 8e).…”

Section: Journal Of Geophysical Research: Solid Earthmentioning

confidence: 98%

“…Near the volcano summit, the extent of the lava flows reached nearly 3 km across the caldera and 10 km in length along the upper SRZ (Caress et al, ; Clague et al, ; Figure ); however, the thickest flows (up to 137 m) were found ~23 km south of the caldera along the SRZ. Most recently, on 24 April 2015, the OOI monitoring network captured a volcanic eruption (Caplan‐Auerbach et al, ; Levy et al, ; Nooner & Chadwick, ; Wilcock, Tolstoy, et al, ; Wilcock et al, ). Inflation before the eruption and deflation during it was accommodated by the reactivation of an outward dipping caldera ring fault, which likely provided a pathway for a dike that propagated both southward and northward beneath the east wall of the caldera (Wilcock, Tolstoy, et al, ).…”

Section: Introductionmentioning

confidence: 99%

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Structure, Seismicity, and Accretionary Processes at the Hot Spot‐Influenced Axial Seamount on the Juan de Fuca Ridge

et al. 2018

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Axial Seamount is the most volcanically active site of the northeast Pacific, and it has been monitored with a growing set of observations and sensors during the last two decades. Accurate imaging of the internal structure of volcanic systems is critical to better understand magma storage processes and to quantify mass and energy transport mechanisms in the crust. To improve the three‐dimensional velocity structure of Axial Seamount, we combined 469,891 new traveltime arrivals, from 12 downward extrapolated seismic profiles, with 3,962 existing ocean‐bottom‐seismometers traveltime arrivals, into a joint tomographic inversion. Our approach reveals two elongated magma reservoirs, with melt fraction up to 65%, representing an unusually large volume of melt (26–60 km3), which is likely the result of enhanced magma supply from the juxtaposition of the Cobb hot spot plume (0.26–0.53 m3/s) and the Axial spreading segment (0.79–1.06 m3/s). The tomographic model also resolves a subsided caldera floor that provides an effective trap for ponding lava flows, via a “trapdoor” mechanism. Our model also shows that Axial's extrusive section is thinnest beneath the elevated volcano, where anomalously thick (11 km) oceanic crust is present. We therefore suggest that focused and enhanced melt supply predominantly thickens the crust beneath Axial Seamount through diking accretion and gabbro crystallization. Lastly, we demonstrate that our three‐dimensional velocity model provides a more realistic starting point for relocating the local seismicity, better resolving a network of conjugate outward and inward dipping faults beneath the caldera walls.©2018. The Authors.

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Section: Discussionsupporting

confidence: 85%

Section: Journal Of Geophysical Research: Solid Earthmentioning

confidence: 65%

Section: Journal Of Geophysical Research: Solid Earthmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

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Structure, Seismicity, and Accretionary Processes at the Hot Spot‐Influenced Axial Seamount on the Juan de Fuca Ridge

et al. 2018

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“…As observed in previous studies that relocated earthquakes with 1-D velocity models (Levy et al, 2018;Wilcock et al, 2016) and a 3-D V P model (Arnulf et al, 2018), the distribution of earthquakes under Axial Seamount defines, in map view, a figure eight pattern with high earthquake densities around the caldera and across its center ( Figure S16), this pattern is truncated to the north by low earthquake densities in the northern caldera ( Figure S16). However, our catalog differs in some significant ways.…”

Section: Earthquakes Distributionsupporting

confidence: 76%

A Joint Inversion for Three‐dimensional P and S Wave Velocity Structure and Earthquake Locations Beneath Axial Seamount

et al. 2019

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Axial Seamount is a prominent volcano located at the intersection of the Juan de Fuca Ridge and the Cobb‐Eickelberg hot spot in the northeast Pacific Ocean that has erupted in 1998, 2011, and 2015. The 2015 eruption was recorded by a seven‐station seismic network in the southern part of the summit caldera that forms part of the Ocean Observatories Initiative Cabled Array. We utilize a data set of ~3,900 well‐recorded earthquakes from January 2015 to February 2017 and a three‐dimensional P wave velocity model obtained previously from active source data to conduct a joint inversion for three‐dimensional P and S wave velocities and hypocentral parameters. The resulting velocity models are used to relocate >76,000 earthquakes with ≥10 arrival times. The velocity models reveal a low‐velocity anomaly in the center of the southern caldera at depths less than ~2 km, which corresponds to the top of the magma chamber and is interpreted as a region that is intensely fractured by the cyclical deformation of the caldera. High velocities around the caldera rim are likely due to consolidated undeformed lava flows. Low VP/VS in the southern caldera is consistent with the presence of hydrothermal vapor. Low S wave velocities and high VP/VS in the northern caldera may indicate a region dominated by thin cracks caused by dike injection. The relocated earthquakes delineate outward‐dipping ring faults more clearly than previous studies and image a subvertical inward‐dipping fault within the network that connects to the east caldera wall and eruptive fissures.

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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

Chadwick

Wilcock

Nooner

et al. 2021

Preprint

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Axial Seamount is a basaltic hot spot volcano with a summit caldera at a depth of ˜1500 m below sea level, superimposed on the Juan de Fuca spreading ridge, giving it a robust and continuous magma supply. Axial erupted in 1998Axial erupted in , 2011Axial erupted in , and 2015 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 2011-2015, 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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Mechanics of fault reactivation before, during, and after the 2015 eruption of Axial Seamount

Cited by 33 publications

References 18 publications

Structure, Seismicity, and Accretionary Processes at the Hot Spot‐Influenced Axial Seamount on the Juan de Fuca Ridge

Structure, Seismicity, and Accretionary Processes at the Hot Spot‐Influenced Axial Seamount on the Juan de Fuca Ridge

A Joint Inversion for Three‐dimensional P and S Wave Velocity Structure and Earthquake Locations Beneath Axial Seamount

Geodetic Monitoring at Axial Seamount Since its 2015 Eruption Reveals a Waning Magma Supply and Tightly Linked Rates of Deformation and Seismicity

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