The exploration and exploitation of the hydro-geothermal resources require a proper understanding of the crustal rocks mechanical behaviour and of how the transition from brittle to ductile deformation (BDT) occurs. These topics have been previously investigated mostly through rheological experiments and numerical models. In this study, we investigate how the crustal mechanical deformation correlates to depth variations of seismic attenuation. This parameter provides an alternative assessment of the BDT and ductile conditions within the crust. We rely on a numerical method, developed by Farina et al. (10.1016/j.geothermics.2019.05.005), in which the Burgers and Gassmann mechanical model are incorporated to derive shear wave attenuation (), which is then related to the rock’s rheology through a shear viscosity parameter. For this purpose, we considered a wide range of rock rheology (dry and wet) thermal conditions, and strain rates values. This allows us to establish thermo-mechanical conditions at which the BDT occurs and to cross correlate this transition to computed shear seismic wave attenuation values. We observe that variations with depth are more influenced by the input strain rate than rock‘s rheology and thermal conditions, so that a fixed amount of Qs reduction can be used as a metric to identify an average BDT depth for each strain rate used. Below this depth, we observe a significant reduction in Qs (up to 10-4 % of the surface value), which depends on a second-order to the rocks’ temperature and rheology. We further demonstrate how Qs variation as function of temperature can be quantitatively described via a third order polynomial function, determined by the rock’s rheology and, to a lesser extent, by the imposed strain rate conditions. Since the greatest Qs reduction is estimated for the greatest input strain rate (10-13 s-1) and temperatures, the proposed method can find more applicability in tectonically active/geothermal areas.
A numerical approch to link the mechanical deformation with seismic attenuation of the crustal rocks
Natale Castillo M. A.
;Tesauro M.Supervision
;
2022-01-01
Abstract
The exploration and exploitation of the hydro-geothermal resources require a proper understanding of the crustal rocks mechanical behaviour and of how the transition from brittle to ductile deformation (BDT) occurs. These topics have been previously investigated mostly through rheological experiments and numerical models. In this study, we investigate how the crustal mechanical deformation correlates to depth variations of seismic attenuation. This parameter provides an alternative assessment of the BDT and ductile conditions within the crust. We rely on a numerical method, developed by Farina et al. (10.1016/j.geothermics.2019.05.005), in which the Burgers and Gassmann mechanical model are incorporated to derive shear wave attenuation (), which is then related to the rock’s rheology through a shear viscosity parameter. For this purpose, we considered a wide range of rock rheology (dry and wet) thermal conditions, and strain rates values. This allows us to establish thermo-mechanical conditions at which the BDT occurs and to cross correlate this transition to computed shear seismic wave attenuation values. We observe that variations with depth are more influenced by the input strain rate than rock‘s rheology and thermal conditions, so that a fixed amount of Qs reduction can be used as a metric to identify an average BDT depth for each strain rate used. Below this depth, we observe a significant reduction in Qs (up to 10-4 % of the surface value), which depends on a second-order to the rocks’ temperature and rheology. We further demonstrate how Qs variation as function of temperature can be quantitatively described via a third order polynomial function, determined by the rock’s rheology and, to a lesser extent, by the imposed strain rate conditions. Since the greatest Qs reduction is estimated for the greatest input strain rate (10-13 s-1) and temperatures, the proposed method can find more applicability in tectonically active/geothermal areas.Pubblicazioni consigliate
I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
