What controls Coulomb stress changes on thrust and normal faults? Insights from three-dimensional finite-element models including pore fluid pressure changes and postseismic viscoelastic relaxation
Final Report Abstract
Intra-continental faults pose a substantial seismic hazard to populated areas but their potential to cause major earthquakes has received less attention than the earthquake hazard at plate boundaries. Prominent examples of devastating intra-continental earthquakes include the 2008 Wenchuan (China) earthquake and the 2009 L'Aquila and 2016 Norcia-Amatrice (Italy) events. In addition to the immediate damage, a large earthquake on a source fault causes stress changes on adjacent faults (= receiver faults), which may ultimately trigger or delay subsequent earthquakes. The alteration of a receiver fault's stress state can be expressed in terms of Coulomb stress changes, which are caused by the coseismic displacement and transient postseismic processes including poroelastic effects and viscoelastic relaxation. In the project, we investigated the earthquakeinduced deformation and the stress transfer between dip-slip faults by 2D and 3D finite-element modelling. To isolate the effects of pore fluid flow and viscoelastic relaxation from each other, we performed experiments with and without pore fluid flow and viscoelastic relaxation, respectively, and varied the permeability and viscosity of the crustal layers. Our model results show that coseismic (= static) Coulomb stress changes are immediately altered by poroelastic effects and viscoelastic relaxation during the first month after the earthquake. Poroelastic effects dominate the crustal deformation and stress changes in the first months after the earthquake, while the signal from viscoelastic relaxation may be recognizable between six months to decades after the earthquake, depending on the viscosity of the crust. Poroelastic effects may nevertheless still occur if the permeability of the upper crust is sufficiently low. As a result, Coulomb stress changes caused by poroelastic effects, viscoelastic relaxation and interseismic stress accumulation may overlap for decades. With respect to spatial scales, our results show that pore fluid pressure changes affect the velocity field mostly within 10-20 km around the fault, whereas the signal from viscoelastic relaxation is recognizable up to several tens of kilometres away from the fault. Our findings reveal that poroelastic effects and viscoelastic relaxation overlap earlier and over longer time periods than previously thought, which should be considered when interpreting aftershock distributions, Coulomb stress changes and surface displacements. Both poroelastic and viscoelastic effects have a strong impact on the magnitudes and patterns of Coulomb stress changes and should therefore be considered together when analysing Coulomb stress transfer between faults. Our findings further imply that the widely applied approach of using static stress changes to evaluate the stress transfer between faults generally leads to invalid results because transient processes significantly alter the coseismic stress changes.
Publications
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2D finite-element modelling of the interaction between poroelastic effects and viscoelastic relaxation during the seismic cycle. DGGV Annual Meeting GeoKarlsruhe (online talk).
Peikert, J.; A. Hampel & M. Bagge
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2D finite-element modelling of the interaction between poroelastic effects and viscoelastic relaxation during the seismic cycle. EGU General Assembly (online presentation).
Peikert, J.; A. Hampel & M. Bagge
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Relative importance of poroelastic effects and viscoelastic relaxation for postseismic velocity fields after normal and thrust earthquakes: insights from 2D finite-element modelling. DGGV Annual Meeting, GeoMin Köln (talk).
Peikert, J.; A. Hampel & M. Bagge
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Relative importance of poroelastic effects and viscoelastic relaxation for postseismic velocity fields after normal and thrust earthquakes: Insights from 2D finite-element modelling. Tectonophysics, 838, 229477.
Peikert, Jill; Hampel, Andrea & Bagge, Meike
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Relative Importance of Poroelastic Effects and Viscoelastic Relaxation for Postseismic Velocity Fields and Coulomb Stress Changes on Normal and Thrust faults: Insights from Finite-Element Modeling. AGU Fall Meeting, Chicago, poster.
Peikert, J.; A. Hampel & M. Bagge
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Relative Importance of Poroelastic Effects and Viscoelastic Relaxation for Co- and Postseismic Coulomb Stress Changes on Normal and Thrust faults: Insights from 3D Finite-Element Modeling. EGU General Assembly, Vienna, poster.
Peikert, J.; A. Hampel & M. Bagge
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Three-dimensional finite-element modeling of Coulomb stress changes on normal and thrust faults caused by pore fluid pressure changes and postseismic viscoelastic relaxation. Geosphere, 20(1), 105-128.
Peikert, Jill; Hampel, Andrea & Bagge, Meike
