Physically Consistent Modeling of Dike‐Induced Deformation and Seismicity: Application to the 2014 Bárðarbunga Dike, Iceland

Abstract

Dike intrusions are often associated with surface deformation and propagating swarms of earthquakes. These are understood to be manifestations of the same underlying physical process, although rarely modeled as such. We construct a physics‐based model of the 2014 Bárðarbunga dike, by far the best observed large dike ( >0.5 km 3) to date. We constrain the background stress state by the total dike deformation, the time‐dependent dike pressure from continuous GPS and the extent of the seismic swarm, and the spatial dependence of frictional properties via the space‐time evolution of seismicity. We find that the geodetic and earthquake data can be reconciled with a self‐consistent set of parameters. The complex spatial and temporal evolution of the Bárðarbunga seismicity can be explained by dike‐induced elastic stress changes on preexisting faults, constrained by observed focal mechanisms. In particular, the model captures the segmentation of seismicity, where only the newest dike segment is seismically active. Our results indicate that many features of the seismicity result from the interplay between time‐dependent magma pressure within the dike and stress memory effects. The spatial variability in seismicity requires heterogeneity in frictional properties and/or local initial stresses. Modeling suggests that the dike pressure drops during rapid advances and increases during pauses, which primarily causes the segmentation of the seismicity. Joint analysis of multiple data types could potentially lead to improved, physics‐based eruption forecasts.

Intense Seismicity During the 2014–2015 Bárðarbunga‐Holuhraun Rifting Event, Iceland, Reveals the Nature of Dike‐Induced Earthquakes and Caldera Collapse Mechanisms

“…Each dike segment went seismically “quiet” once a segment was intruded beyond it. Magma pressure reaches its maximum in a given segment after it has stalled and inflated for an extended period, corresponding to the maximum stress being induced on preexisting faults in its vicinity (Heimisson & Segall, ). When the dike next advances, the pressure and induced stress drops, and seismicity ceases.…”

Aseismic Deformation During the 2014 Mw 5.2 Karonga Earthquake, Malawi, From Satellite Interferometry and Earthquake Source Mechanisms

“…Throughout dike emplacement and surface breach, the seismicity remained at 5‐ to 7‐km depth (Ágústsdóttir et al., 2016), corresponding to around the base of the modeled dike. Meanwhile, the dike opening (maximum at <3‐km depth) occurred aseismically (e.g., Heimisson & Segall, 2020; Woods et al., 2019), indicating the role of shallow, weak crust in accommodating aseismic deformation. In the absence of magmatism, the shallow weakened zones are probably similar to the brittle and fractured limestone units in the upper crust of the L'Aquila fault, where foreshocks and aftershocks to the 2009 M w 6.0 mainshock outlined multiple secondary synthetic and antithetic faults (Chiaraluce et al., 2011).…”

Unexpected large eruptions from buoyant magma bodies within viscoelastic crust

“…Such moderate to large effusive basaltic eruptions and the preceding long-term magma accumulation, modulated by tectonics and mantle plume activity, provide a challenge for commonly used mechanical volcano models. This is clearly illustrated by the 2014-2015 activity in the Bárðarbunga volcanic system, when gradual caldera collapse occurred over a period of 6 months in response to drainage of magma from below the caldera, initially along a lateral dike 5,8 that fed a major effusive eruption 45 km away at Holuhraun (Supplementary Note 1). Several lines of evidence (ground deformation, petrology and seismic activity) 4,5 suggest that the magma came from a single magma body located at a depth of 10 ± 3 km beneath the surface of the ice-filled caldera, below the brittle-ductile transition 4,7,9 .…”