HR: 0800h
AN: H11B-0479    [Abstracts]
TI: Linking fault permeability, fluid flow, and earthquake triggering in a hydrothermally active tectonic setting: Numerical Simulations of the hydrodynamics in the Tjörnes Fracture Zone, Iceland.
AU: * Lupi, M
EM: matteo.lupi@pet.hw.ac.uk
AF: Institute of Petroleum Engineering, Heriot Watt University, Edinburgh, EH14 4AS, United Kingdom
AU: * Lupi, M
EM: matteo.lupi@pet.hw.ac.uk
AF: ECOSSE, University of Edinburgh & Heriot Watt University, Edinburgh, EH14 4AS, United Kingdom
AU: Geiger, S
EM: sebastian.geiger@hw.ac.uk
AF: Institute of Petroleum Engineering, Heriot Watt University, Edinburgh, EH14 4AS, United Kingdom
AU: Geiger, S
EM: sebastian.geiger@hw.ac.uk
AF: ECOSSE, University of Edinburgh & Heriot Watt University, Edinburgh, EH14 4AS, United Kingdom
AU: Graham, C
EM: colin.graham@ed.ac.uk
AF: ECOSSE, University of Edinburgh & Heriot Watt University, Edinburgh, EH14 4AS, United Kingdom
AU: Graham, C
EM: colin.graham@ed.ac.uk
AF: School of Geosciences, University of Edinburgh, Edinburgh, EH9 3JW, United Kingdom
AU: Claesson, L
EM: lillemor.claesson@geo.su.se
AF: Department of Geology and Geochemistry, Stockholm University, Stockholm, 106 91, Sweden
AU: Claesson, L
EM: lillemor.claesson@geo.su.se
AF: Icelandic Geosurvey, Grensasvegi 9, Reykjavik, 108, Iceland
AU: Richter, B
EM: bjarni.richter@isor.is
AF: Icelandic Geosurvey, Grensasvegi 9, Reykjavik, 108, Iceland
AB: A good insight into the transient fluid flow evolution within a hydrothermal system is of primary importance for the understanding of several geologic processes, for example the hydrodynamic triggering of earthquakes or the formation of mineral deposits. The strong permeability contrast between different crustal layers as well as the high geothermal gradient of these areas are elements that strongly affect the flow behaviour. In addition, the sudden and transient occurrence of joints, faults and magmatic intrusions are likely to change the hydrothermal flow paths in very short time. The Tjörnes Fracture Zone (TFZ) north of Iceland, is such a hydrothermal area where a high geothermal gradient, magmatic bodies, faults, and the strong contrast between sediments and fractured lava layers govern the large-scale fluid flow. The TFZ offsets the Kolbeinsey Ridge and the Northern Rift Zone. It is characterized by km-scale faults that link sub-seafloor sediments and lava layers with deeper crystalline rocks. These structures focus fluid flow and allow for the mixing between cold seawater and deep hydrothermal fluids. A strong seismic activity is present in the TFZ: earthquakes up to magnitude 7 have been recorded over the past years. Hydrogeochemical changes before, during and after a magnitude 5.8 earthquake suggest that the evolving stress state before the earthquake leads to (remote) permeability variations, which alter the fluid flow paths. This is in agreement with recent numerical fluid flow simulations which demonstrate that fluid flow in magmatic- hydrothermal systems is often convective and very sensitive to small variations in permeability. In order to understand the transient fluid flow behaviour in this complex geological environment, we have conducted numerical simulations of heat and mass transport in two geologically realistic cross-sectional models of the TFZ. The geologic models are discretised using finite element and finite volume methods. They hence have a very high resolution that allows us to investigate the influence of high-aspect ratio structures like faults and thin sedimentary layers on the large-scale fluid flow behaviour in detail. Our numerical simulations account for transient variations of permeability due to mineral precipitation and the abrupt breaking of the rocks caused by hydrofracturing. We also consider different and discontinuous amounts of magmatic fluid production from crystallising intrusions. This allows us to understand how large-scale fluid flow responds to transient permeability variations and how those can trigger earthquakes in magmatic-hydrothermal systems like the Tjörnes Fracture Zone.
DE: 1829 Groundwater hydrology
DE: 5104 Fracture and flow
DE: 8010 Fractures and faults
DE: 8020 Mechanics, theory, and modeling
DE: 8045 Role of fluids
SC: Hydrology [H]
MN: 2007 Fall Meeting