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Abstract Surface deformation and seismicity provide critical information to understand the dynamics of volcanic unrest. During 2006–2007, >80 mm/yr uplift was observed by interferometric synthetic aperture radar (InSAR) at the central Atka volcanic center, Alaska, coinciding with an increasing seismicity rate. On November 25, 2006, a phreatic eruption occurred at the Korovin volcanic vent, 5‐km north of the central Atka, following the drainage of its crater lake a month prior to the eruption. The InSAR data are assimilated into three‐dimensional finite element models using the Ensemble Kalman Filter to investigate: (1) the pressure source creating the surface deformation; (2) the triggering of the volcano‐tectonic (VT) earthquakes in the Atka volcanic center; and (3) the triggering of the phreatic eruption at Korovin. The models show that the pressure source required to create the surface deformation is a NE‐tilted, oblate ellipsoid, which rotated from steep to gentle dipping from June to November 2006 before the eruption. The modeled dilatancy in a pre‐existing weak zone, coinciding with the Amlia‐Amukta fault, driven by the pressure source has a spatial and temporal correlation with the evolution of the VT earthquakes during the unrest. The fault dilatancy may have increased the connected porosity and permeability of the fault zone allowing fluid injection which triggered the observed seismicity. In addition, the dilatated fault may have increased the fluid capacity of the fault zone by ∼105 m3, causing the discharge of the crater lake at Korovin. Consequently, the phreatic eruption of the Korovin volcano may have been triggered.
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Fault–Dike–Magma Interactions Inferred from Transcrustal Conical Structures under Akutan Volcano
Volcano monitoring and eruption forecasting require accurate characterization of transcrustal magmatic structures to place volcanic unrest in context within the system where it occurs. Structural imaging using local seismicity is limited to seismogenic depths. Here, we exploit arrivals in teleseismic receiver functions that change polarity with backazimuth to image two surfaces beneath Akutan volcano in the Aleutian arc. The two surfaces delineate an upper to midcrustal inverted conical volume that deepens and thickens away from the volcanic center, with thicknesses of 3–13 km. The top of the volume is at depths of 2–3 km below sea level at distances of ∼5–15 km from the caldera center. The bottom is at depths of 7–15 km at the same distances, and the cone’s thickness increases outward from ∼5 to ∼10 km. The signal is best fit by a volume with anisotropy with fast symmetry planes that dip outward from the center and downward increases in shear velocity at both interfaces. The upper boundary coincides with the top of Akutan’s volcanotectonic (VT) seismogenic zone, with the VT seismicity exhibiting outward dipping planar features that match the anisotropic fast plane orientation within the volume. The bottom of the anisotropic volume is below the termination depth of the majority of the VT seismicity and is therefore likely associated with the brittle–ductile transition. Long-period (LP) events associated previously with magma movement are concentrated below the anisotropic VT volume. Because of the strong spatial association with VT seismicity, we interpret the volume as consisting of concentric outward dipping faults and dikes that align the seismogenic response to stress changes from magmatic processes. Our observations map this volume independent of the present-day seismicity distribution and thus provide a spatially more complete image of the magmatic system.
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- PAR ID:
- 10530657
- Publisher / Repository:
- Seismological Society of America
- Date Published:
- Journal Name:
- Seismological Research Letters
- ISSN:
- 0895-0695
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1785/0220240119
