MagmaCourse: Fluid pathways below the Eger Rift constrained by numerical and analog simulations.
Geophysics
Final Report Abstract
In this project we extended fluid-filled fracture propagation models to three dimensions (3D). We did so developing both analytical and numerical schemes that work in 3D. In our analytical method, we approximate the propagating 3D fracture as a penny-shaped crack that is influenced by both an internal pressure and stress gradients. In our numerical method, we model propagation of fractures simulated as a mesh of triangular dislocations, with the displacement of faces computed using the displacement discontinuity method. We devise a rapid technique to approximate stress intensity at the dislocations sitting on the edges and use this to calculate the advance of the fracture’s tip-line. This results in fractures that can bend or twist in a complex stress field. Our 3D models can be applied to arbitrary stresses, topographic and crack shapes, whilst retaining short computation times. We published the codes on GitHub. We cross-validate our analytical and numerical methods and apply them to various natural and man-made settings, to gain additional insights into the movements of hydraulic fractures such as magmatic dikes and fluid injections in rock. In particular, we calculate the ’volumetric tipping point’, which once exceeded allows a fluid-filled fracture to propagate in a ’self-sustaining’ manner. We discuss implications for CO2 or magma injections, such as in the Eger Rift, or for hydro-fracturing in industrial operations. We also developed models to constrain the stress field in volcanic areas such as rifts or calderas by first formulating the stress field as a superposition of different effects including tectonic stress and surface loading, and then calibrate the relative weight of these factors by requiring that modelled magma trajectories and vent locations match with observations. Finally, we address the mechanics of 3D propagating dykes and sills in volcanic regions. We first focus on rift settings through analogue experiments and show that magma trajectories, storage geometry and vent locations can be forecast by constraining the ratio between topographic to remote stresses. We focus then on Sierra Negra volcano in the Galápagos, where in 2018 a sill propagated with an extremely curved trajectory. Using our 3D analysis, we find that shallow sills are highly sensitive to topographic and buoyancy stress gradients, as well as the effects of the free surface. “Surprises” found during the research: • The volumes required before a fracture ascends in a self-sustained manner are of the same order of magnitude relative to industrial injection volumes. • Flat-lying magma bodies are highly sensitive to the overlying topography, stress gradients define the way these propagate. • Rifts deflect magmatism towards their flanks due to unloading stresses. The location of volcanism depends on the ratio of the unloading stress and extensional stresses opening the rift. Numerical models can successfully predict the location of the next eruption provided the stress state is known. https://www.gfz-potsdam.de/en/media-and-communication/news/ details/article/how-to-recognise-where-a-volcano-will-erupt/ https://www.deutschlandfunk.de/vulkanismus-am-vesuv-computermodell-soll-vorhersagen-an.676.de.html?dram:article_id=455292 https://www.sciencefocus.com/news/computer-model-may-help-to-more-accuratelypredict-volcano-eruptions/
Publications
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Slip on wavy frictional faults: Is the 3rd dimension a sticking point?. Journal of Structural Geology, 119(c(2019, 2)), 33-49.
Davis, T.; Healy, D. & Rivalta, E.
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Stress inversions to forecast magma pathways and eruptive vent location. Science Advances, 5(7).
Rivalta, E.; Corbi, F.; Passarelli, L.; Acocella, V.; Davis, T. & Di Vito, M. A.
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Critical Fluid Injection Volumes for Uncontrolled Fracture Ascent. Geophysical Research Letters, 47(14).
Davis, Timothy; Rivalta, Eleonora & Dahm, Torsten
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Extreme Curvature of Shallow Magma Pathways Controlled by Competing Stresses: Insights From the 2018 Sierra Negra Eruption. Geophysical Research Letters, 48(13).
Davis, Timothy; Bagnardi, Marco; Lundgren, Paul & Rivalta, Eleonora
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Stress Inversion in a Gelatin Box: Testing Eruptive Vent Location Forecasts With Analog Models. Geophysical Research Letters, 48(6).
Mantiloni, L.; Davis, T.; Gaete Rojas, A. B. & Rivalta, E.
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The 2014 Juan Fernández microplate earthquake doublet: Evidence for large thrust faulting driven by microplate rotation. Tectonophysics, 801(c(2021, 2)), 228720.
Cesca, Simone; Valenzuela Malebrán, Carla; López-Comino, José Ángel; Davis, Timothy; Tassara, Carlos; Oncken, Onno & Dahm, Torsten
