Revised Magmatic Source Models for the 2015 Eruption at Axial Seamount Including Estimates of Fault‐Induced Deformation

Abstract

Axial Seamount is an active submarine volcano located at the intersection of the Cobb hot spot and the Juan de Fuca Ridge (45°57′N, 130°01′W). Bottom pressure recorders captured co‐eruption subsidence of 2.4–3.2 m in 1998, 2011, and 2015, and campaign‐style pressure surveys every 1–2 years have provided a long‐term time series of inter‐eruption re‐inflation. The 2015 eruption occurred shortly after the Ocean Observatories Initiative (OOI) Cabled Array came online providing real‐time seismic and deformation observations for the first time. Nooner and Chadwick (2016, https://doi.org/10.1126/science.aah4666) used the available vertical deformation data to model the 2015 eruption deformation source as a steeply dipping prolate‐spheroid, approximating a high‐melt zone or conduit beneath the eastern caldera wall. More recently, Levy et al. (2018, https://doi.org/10.1130/G39978.1) used OOI seismic data to estimate dip‐slip motion along a pair of outward‐dipping caldera ring faults. This fault motion complicates the deformation field by contributing up to several centimeters of vertical seafloor motion. In this study, fault‐induced surface deformation was calculated from the slip estimates of Levy et al. (2018, https://doi.org/10.1130/G39978.1) then removed from vertical deformation data prior to model inversions. Removing fault motion resulted in an improved model fit with a new best‐fitting deformation source located 2.11 km S64°W of the source of Nooner and Chadwick (2016, https://doi.org/10.1126/science.aah4666) with similar geometry. This result shows that ring fault motion can have a significant impact on surface deformation, and future modeling efforts need to consider the contribution of fault motion when estimating the location and geometry of subsurface magma movement at Axial Seamount.

Triggering of eruptions at Axial Seamount, Juan de Fuca Ridge

“…6). This hypothesis is supported by a recent investigation which distinguished contributions from faulting and reservoir expansion to total surface deformation at Axial Seamount and found that fault slip was an important contribution to total deformation for the 2015 eruption cycle 54 .…”

Stacked Magma Lenses Beneath Mid‐Ocean Ridges: Insights From New Seismic Observations and Synthesis With Prior Geophysical and Geologic Findings

“…Carbotte et al. (2020) interpret the series of vertically stacked magma lenses detected beneath Axial Seamount as similar mush compaction features based on numerical modeling, observations of lens spacing, and colocation with the deep conduit where active porous flow is inferred from long‐term geodetic measurements of volcano inflation (Hefner et al., 2020; Nooner & Chadwick, 2016). Given these findings, our favored interpretation for the similar stacked magma lenses detected beneath the JdF Ridge and elsewhere beneath MORs, which locate in the most melt rich portion of the axial crust, in locations where other observations support active melt replenishment, as melt segregations due to compaction of a mush undergoing porous flow (Figure 8).…”

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

“…(2020), “+” symbol is approximate center of sills, X's are centroids of best‐fit deformation models of Nooner and Chadwick (2016) at right and Hefner et al. (2020) at left, black squares are OOI seismometer locations, light‐ and dark‐gray areas are lava flows erupted in 2011 and 2015, respectively. Similar maps for the other short‐term deflation events are provided in Supporting Information .…”

“…This enables continuous long‐term monitoring with real‐time data from a diverse set of instrumentation. For example, the cabled observatory was in place during the April 2015 eruption, providing an extraordinary inter‐disciplinary data set that has been used to interpret that event in rich detail (Baillard et al., 2019; Caplan‐Auerbach et al., 2017; Clague et al., 2017, 2018; Hefner et al., 2020; Le Saout et al., 2020; Levy et al., 2018; Nooner & Chadwick, 2016; Waldhauser et al., 2020; Wilcock et al., 2016; Xu et al., 2018). Other data sets that provide valuable information on the crustal structure and magma storage system beneath Axial Seamount were collected by a seismic tomography study (West et al., 2001) and two multi‐channel seismic reflection surveys, one 2‐D survey performed in 2002 (Arnulf et al., 2014, 2018) and a 3‐D survey in 2019 (Arnulf et al., 2019, 2020), which have revealed the location and geometry of a large shallow magma reservoir 1.5–2.5 km below the caldera, and a series of deeper stacked sills from 2.5 to 4.5 km depth below the southern caldera (Carbotte et al., 2020).…”