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

• Applicant: Professorin Dr. Andrea Hampel
• Subject Area: Palaeontology
• Term: from 2020 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 437915117

Earthquakes on 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. Recent 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 other earthquakes. The alteration of a receiver fault's stress state is typically expressed in terms of Coulomb stress changes, which are caused by the coseismic displacement and transient postseismic processes including poroelastic effects and viscoelastic relaxation. So far, many studies of Coulomb stress changes have focussed on individual earthquakes and faults in nature, for which the contributions of transient and non-transient processes often remain highly controversial. The main reason for this ambiguity is that the direct measurement of Coulomb stress changes is currently impossible and that Coulomb stress change analyses are therefore based solely on model calculations, which must use simplifying assumptions concerning fault geometry or the implementation of transient processes. For example, the widely used software Coulomb does not consider poroelastic or viscoelastic effects at all. In addition, there is a lack of conceptual models that provide information on theoretically expected stress change patterns and a base for comparison with stress changes induced by natural earthquakes.The goal of the proposed project is to advance our understanding how transient and non-transient mechanisms control co- and postseismic Coulomb stress changes on intra-continental thrust and normal faults. As a method, we will apply 3D finite-element modelling with the software ABAQUS. The model faults will be implemented as frictional contact interfaces, which accumulate slip according to the temporarily evolving stress and strain fields in the model. In different experiment, we will vary the dip and dip direction of the receiver faults as well as their positions with respect to the source fault. All models will include gravity, isostasy and a regional stress field owing to extension or shortening of the model. As causes of Coulomb stress changes, the earthquake magnitude, poroelastic effects, postseismic viscoelastic relaxation and interseismic stress accumulation will be considered. By implementing this range of processes, we will provide the first systematic evaluation of their relative importance for co- and postseismic Coulomb stress changes. Furthermore, we will provide a detailed analysis of the spatial and temporal scales of the different processes, which will enable a better differentiation between poroelastic effects and postseismic viscoelastic relaxation in natural Coulomb stress change patterns.

• DFG Programme: Research Grants