Investigation of interactions between fluids and earthquakes based on numerical modelling

Diplôme Thèse Investigation of interactions between fluids and earthquakes based on numerical modelling eng 2023 2023 author Marguin Valentin 931163 director Simpson Guy 653721 Services communs du département des sciences de la terre (DETCO) 146 10.13097/archive-ouverte/unige:174880 urn:nbn:ch:unige-1748800 Sc. 5794 The strength and sliding behaviour of faults in the upper crust are largely controlled by friction and effective stress, which is modulated by the fluid pressure. While many studies have investigated the role of friction on the earthquake cycle, relatively little effort has gone into understanding the effects linked to dynamic changes in fluid pressure. Our study aims to explore the complex interactions between long-term tectonic loading, fluid pressure, rapid fault slip and elastic stress transfer that occur during earthquakes on plane faults in two dimensions. Our models incorporate rate- and state-dependent friction and dramatic changes in the fault permeability during sliding. In some models, we have also incorporated shear heating and thermal pressurisation. Our most basic models consider slow fluid pressure generation during the interseismic period. Conversely, during an earthquakes, the permeability increase enables fluid overpressures to rapidly dissipate. This is commonly known as fault valve behaviour. In these modes, earthquakes are nucleated where fluid pressures are locally high. Ruptures are then propagated as slip pulses onto stronger parts of the fault. Our model produces a wide range of sliding velocities from rapid to slow earthquakes, which occur due to high pore pressures prior to rupture. The models also show evidence of aftershocks driven by fluid transfer along the fault plane after the main shock. Overall, we find that relatively modest fluid overpressures tend to reduce coseismic slip, stress drop, maximum sliding velocity, rupture velocity, and the earthquake recurrence time relative to ruptures in a dry crust. We show that fluids can exert an important influence on earthquakes in the crust, mostly due to modulation of the effective stress and variations in permeability and, to a lesser extent, to poroelastic coupling. For models exhibiting 'valve' behaviour, we observe complex ruptures and swarm activity associated with rising fluid pressure. In addition to 'valve' behaviour, faults are sometimes considered to actively pump fluids into or out of fault zones over the earthquake cycle. We have studied one aspect of this pumping through the incorporation of thermal pressurisation arising from shear heating. Our models show that thermal pressurisation has the effect of increasing the stress drop, coseismic slip and sliding velocity relative to pure valve models. Both pump and valve models can explain anomalously weak faults, though they are each associated with distinctly different fluid pressure and strength evolution over the seismic cycle and during rupture. Finally, in addition to studying slip dynamics we have also examined the fluid pressure fields in the Earth's crust following earthquakes. Much research has focused on post-seismic surface deformation that results from earthquake-induced fluid flow, commonly known as 'poroelastic rebound'. These studies have focused exclusively on fluid flow induced by coseismic volumetric changes in the crust. In our investigation we have studied surface deformation linked to breaching of a pressurised fault zone during rupture. Our study shows that regardless of the fault mechanism (i.e., reverse versus normal), fluid drainage induced by rupture tends to cause surface subsidence above the rupture zone after an earthquake. These observations allow us to interpret better the diversity of post-seismic deformation. Earthquake dynamics Dynamics and mechanics of faulting Fracture and flow Friction Numerical modelling Fluid pressure Permeability and porosity Dewey 550 Fonds national suisse 200021-184626 42 Département des sciences de la Terre 154 false 4ee08460-5480-40af-9d94-c64a96a7d0ff Thesis Public These_Marguin_Valentin-75.pdf 7592481 application/pdf OA OTHER Private 2025-01-01 947b2d543665a39ba80dc74c93cb630670277849eb1ba653595bf0d0b5cfeae6 668dfdc2-269b-4d36-8183-a9ee95753dd8 Imprimatur Public imprimatur.pdf 52571 application/pdf 5f10c454d1513bafe2c15a281c6149a150dfb46096fb08c787b3f3f40f55f12a 50d48cd5-09b3-4ab3-aa18-4f0266e24d3b Publication mode Private 2024-02-10 17-50.pdf 151957 application/pdf 12440cad6c4d0191c723bc3335adf7d452163e6248b0d8549673cfa938cf4cd0 01c21889-5350-4875-bf67-eab5e624db97 Agreement Private Contrat_diffusion_these_v2022_DocuS.pdf 1258940 application/pdf 9e400b11a45f1d356470efe1e82d69eea61daa2ccc02971891e05508b9eb0a76 noreply@unige.ch Adresse effacée openAccess Faculté des sciences / Section des sciences de la Terre et de l'Environnement / Département des sciences de la Terre

Title	Published in	Year	Views	Downloads

Influence of Fluids on Earthquakes Based on Numerical Modeling	Journal of geophysical research. Solid earth	2023	59	59
Investigation of interactions between fluids and earthquakes based on numerical modelling		2023	123	65

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