How Accurately Can We Model Magma Reservoir Failure With Uncertainties in Host Rock Rheology?

Abstract

Forecasting the onset of a volcanic eruption from a closed system requires understanding its stress state and failure potential, which can be investigated through numerical modeling. However, the lack of constraints on model parameters, especially rheology, may substantially impair the accuracy of failure forecasts. Therefore, it is essential to know whether large variations and uncertainties in rock properties will preclude the ability of models to predict reservoir failure. A series of two‐dimensional, axisymmetric models are used to investigate sensitivities of brittle failure initiation to assumed rock properties. The numerical experiments indicate that the deformation and overpressure at failure onset simulated by elastic models will be much lower than the viscoelastic models, when the timescale of pressurization exceeds the viscoelastic relaxation time of the host rock. Poisson's ratio and internal friction angle have much less effect on failure forecasts than Young's modulus. Variations in Young's modulus significantly affect the prediction of surface deformation before failure onset when Young's modulus is < 40 GPa. Longer precursory volcano‐tectonic events may occur in weak host rock (E < 40 GPa) due to well‐developed Coulomb failure prior to dike propagation. Thus, combining surface deformation with seismicity may enhance the accuracy of eruption forecast in these situations. Compared to large and oblate magma systems, small and prolate systems create far less surface uplift prior to failure initiation, suggesting that more frequent measurements are necessary.

High Rates of Inflation During a Noneruptive Episode of Seismic Unrest at Semisopochnoi Volcano, Alaska in 2014–2015

“…Approximately half of all deformation events are intrusive (i.e., not immediately followed by an eruption (Biggs et al, ). Numerical models suggest that frequency of eruption is dependent on timescale of injection (Degruyter & Huber, ; Zhan & Gregg, ), particularly in smaller reservoirs (Gregg et al, ). However, it is unclear whether intrusive events are generally observed to have lower deformation rates than do episodes of intrusion that lead to eruption or if there is a threshold deformation rate for intrusion vs eruption.…”

Integrating Reservoir Dynamics, Crustal Stress, and Geophysical Observations of the Laguna del Maule Magmatic System by FEM Models and Data Assimilation

“…Besides, the structure of Young's modulus used in the models will also affect the failure forecasts. If we underestimate the Young's modulus, the real overpressure to create the same surface deformation will be higher than the model prediction (Zhan & Gregg, ). Our model predicts higher Vp and Vs than the regional velocity models above 5 km (Figure S1), which rules out the possibility of a significant underestimation of the Young's modulus.…”

“…Similar to Zhan and Gregg (2019), host-rock failure initiates as the overpressure of the magma reservoir is increased. The occurrence of Coulomb failure or tensile failure can be predicted by τ>C 0 cosϕ i þ σ n sinϕ i ;…”

Triggering of eruptions at Axial Seamount, Juan de Fuca Ridge

“…www.nature.com/scientificreports www.nature.com/scientificreports/ presented in the supplementary materials. For further discussion of the impact of elastic and viscoelastic properties on results of unrest models we refer the reader to Zhan et al 16 and Head et al 31 , respectively.…”

“…Low-pressure, high-temperature deformation experiments reveal that Young's modulus in particular is highly temperature dependent at brittle-ductile transition temperatures of 600-750 °C 12 . Furthermore, thermomechanical models of volcano deformation have shown that Young's modulus greatly affects predicted surface deformation and strain accumulation [13][14][15] , and a recent investigation showed that rheology strongly impacts failure potential 16 .…”