Fault (geology)

About: Fault (geology) is a research topic. Over the lifetime, 26732 publications have been published within this topic receiving 744535 citations.

Fluid Flow in Fault Zones: Analysis of the Interplay of Convective Circulation and Topographically Driven Groundwater Flow

Abstract: High-permeability faults, acting as preferential pathways for fluid migration, are important geological structures for fluid, energy, and solute transport. This paper examines the interaction of thermally driven convective circulation in a steeply dipping fault zone and groundwater flow through the surrounding country rock that is driven by a regional topographic gradient. We consider a geometry where a fault zone with a homogeneous, isotropic permeability is located beneath a narrow valley in a region with substantial topographic relief. System behavior is best characterized in terms of the large-scale permeabilities of the country rock and the fault zone. Using three-dimensional numerical simulations, we map in permeability space four fluid flow and heat transfer regimes within a fault zone: conductive, advective, steady convective, and unsteady convective. The patterns of fluid flow and/or heat transfer are substantially different in each of these regimes. Maximum discharge temperatures can also be plotted in permeability space; the maximum discharge temperature in the advective regime is in general lower than that in the steady convective regime. A higher basal heat flux expands the convective regime in permeability space, as does a greater fault depth. Higher topographic relief on the regional water table compresses the convective regime, with the advective regime suppressing convective circulation at lower country rock permeabilities. If convective cells with aspect ratios close to 1 cannot form, the steady convective regime is smaller in permeability space, and the boundary between steady and unsteady convection occurs at lower values of fault zone permeability. At low country rock permeabilities a water table gradient along the surface trace of the fault of approximately 0.3% suppresses convective cells; at higher country rock permeabilities, convection can be suppressed by smaller gradients on the water table.

Cenozoic evolution of the eastern Pamir: Implications for strain-accommodation mechanisms at the western end of the Himalayan-Tibetan orogen

Abstract: Detailed field mapping, geochronologic and thermochronologic analyses, and petrologic investigations conducted along the southern segment of the late Cenozoic Kongur Shan extensional system provide new information on the Cenozoic tectonic evolution of the eastern Pamir at the western end of the Himalayan-Tibetan orogen. Field relations and cooling-age patterns in the hanging wall and footwall of the active faults show a southward decrease in the magnitude of east-west extension along the southern Kongur Shan extensional system, from 20 km or less along the Muztaghata massif in the north, to l3 km along the Tashkorgan fault in the south. These results, in conjunction with previously published work on the northern segment of the Kongur Shan extensional system, show a general southward decrease in east-west extension along the entire length of the extensional system, consistent with models of extension primarily driven by oroclinal bending or radial thrusting of the Pamir. Petrologic data, 40 Ar/ 39 Ar cooling ages, and monazite Th-Pb ages from schists and gneisses in the footwall of the southern Kongur Shan normal fault along the Muztaghata massif record two tectonic events that immediately preceded late Miocene initiation of east-west extension: (1) high-grade schists and gneisses experienced upper amphibolite facies metamorphic conditions (9–10 kbar, 700–750 °C) dated as late Oligocene to middle Miocene by in situ ion-microprobe analyses of monazite inclusions in garnet; and (2) high-grade schists and gneisses were subsequently rapidly exhumed to shallow crustal levels in the late Miocene with 40 Ar/ 39 Ar biotite cooling ages of 7.5–9 Ma. Rapid exhumation was accommodated in part by the east-west–striking, south-dipping, Shenti normal fault. Field relations and regional geologic correlations indicate that this exhumation event was related to the formation of the Central Pamir gneiss domes, and the antiformal Muztaghata massif is the eastward continuation of the Sares dome of the Central Pamir. These observations suggest that the antiformal gneiss domes of the Central Pamir have not been offset across the Karakorum right-slip fault from the Qiangtang anticlinorium in Tibet. Instead, we propose that the development of the Central Pamir gneiss domes may have been related to Oligocene-Miocene northward underthrusting and thickening of crust beneath the Pamir.

Architecture and seismotectonics of a regional low‐angle normal fault zone in central Italy

Abstract: Information from surface geology, subsurface geology (boreholes, seismic reflection, and refraction profiles), and seismicity are used to depict the geometry and the possible seismogenic role of the Altotiberina Fault (AF), a low-angle normal fault in central Italy. The AF extends along the inner Umbria region, for a length of ∼70 km, with an average dip of ∼30° and an horizontal displacement up to 5 km. It emerges west of the inner border of the Tiber basin and deepens beneath the Umbria-Marche carbonate fold-and-thrust belt to a depth of 12–14 km. Close to the AF surface trace, low-angle synthetic east dipping normal faults extensively outcrop, whereas high-angle antithetic west dipping normal faults prevail farther east. Integrating geological and seismologic information, it can be stated that the AF behaves as an active extensional fault zone and represents the basal detachment of the west dipping seismogenic normal faults of the Umbria-Marche region. The AF belongs to a regional NE dipping low-angle normal fault system (Etrurian Fault System (EFS)), which extends for ∼350 km from northwestern Tuscany to southern Umbria. Early preliminary considerations suggest that the EFS may play an important role in controlling active extension and related seismicity in northern central Italy.

Theoretical Considerations of Sealing and Non-Sealing Faults

Abstract: Differentiating between sealing and non-sealing faults and their effects on the subsurface is a major problem in petroleum exploration, development, and production. The fault-seal problem has been investigated from a theoretical viewpoint in order to provide a basis for a better understanding of sealing and non-sealing faults. Some general theories of hydrocarbon entrapment are reviewed and related directly to hypothetical cases of faults as barriers to hydrocarbon migration and faults as paths for hydrocarbon migration. The phenomenon of fault entrapment reduces to a relation between (1) capillary pressure and (2) the displacement pressure of the reservoir rock and the boundary rock material along the fault. Capillary pressure is the differential pressure between the hyd ocarbons and the water at any level in the reservoir; displacement pressure is the pressure required to force hydrocarbons into the largest interconnected pores of a preferentially water-wet rock. Thus the sealing or non-sealing aspect of a fault can be characterized by pressure differentials and by rock capillary properties. Theoretical studies show that the fault seal in preferentially water-wet rock is related to the displacement pressure of the media in contact at the fault. Media of similar displacement pressure will result in a non-sealing fault to hydrocarbon migration. Media of different displacement pressure will result in a sealing fault, provided the capillary pressure is less than the boundary displacement pressure. The trapping capacity of a boundary, in terms of the thickness of hydrocarbon column, is related to the magnitude of the difference in displacement pressures of the reservoir and boundary rock. If the thickness of the hydrocarbon column exceeds the boundary trapping capacity, the excess hydrocarbons will be displaced into the boundary material. Dependent on the conditions, lateral m gration across faults or vertical migration along faults will occur when the boundary trapping capacity is exceeded. Application of the theoretical concepts to subsurface studies should prove useful in understanding and in evaluating subsurface fault seals.