Fault (geology)

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

Constraints on present‐day Basin and Range deformation from space geodesy

Abstract: We use new space geodetic data from very long baseline interferometry and satellite laser ranging combined with other geodetic and geologic data to study contemporary deformation in the Basin and Range province of the western United States. Northwest motion of the central Sierra Nevada block relative to stable North America, a measure of integrated Basin and Range deformation, is 12.1±1.2 mm/yr oriented N38°W±5° (one standard error), in agreement with previous geological estimates within uncertainties. This velocity reflects both east-west extension concentrated in the eastern Basin and Range and north-northwest directed right lateral shear concentrated in the western Basin and Range. Ely, Nevada is moving west at 4.9±1.3 mm/yr relative to stable North America, consistent with dip-slip motion on the north striking Wasatch fault and other north striking normal faults. Comparison with ground-based geodetic data suggests that most of this motion is accommodated within ∼50 km of the Wasatch fault zone. Paleoseismic data for the Wasatch fault zone and slip rates based on seismic energy release in the region both suggest much lower slip rates. The discrepancy may be explained by some combination of additional deformation away from the Wasatch fault itself, aseismic slip, or a seismic rate that is anomalously low with respect to longer time averages. Deformation in the western Basin and Range province is also largely confined to a relatively narrow boundary zone and in our study area is partitioned into the eastern California shear zone, accommodating 10.7±1.6 mm/yr of north-northwest directed right-lateral shear, and a small component (∼1 mm/yr) of west-southwest - east-northeast extension. A slip rate budget for major strike-slip faults in our study area based on a combination of local geodetic or late Quaternary geologic data and the regional space geodetic data suggests the following rates of right-lateral slip: Owens Valley fault zone, 3.9±1.1 mm/yr; Death Valley-Furnace Creek fault zone, 3.3±2.2 mm/yr; White Mountains fault zone in northern Owens Valley, 3.4±1.2 mm/yr; Fish Lake Valley fault zone, 6.2±2.3 mm/yr. In the last few million years the locus of right-lateral shear in the region has shifted west and become more north trending as slip on the northwest striking Death Valley-Furnace Creek fault zone has decreased and is increasingly accommodated on the north-northwest striking Owens Valley fault zone.

Quaternary normal and reverse faulting and the state of stress in the central Andes of south Peru

Abstract: Field studies in the Andes of southern Peru show that in the High Andes and Pacific Lowlands, Quaternary and Recent faults are normal. This extensional tectonics postdates compressional deformations of Pliocene-early Quaternary age. In the sub-Andes the observed deformations are compressional; they affect early Quaternary deposits. Some of the faults separate Quaternary deposits from the bedrock and thus are clearly of tectonic origin and not landslide effects. Striations on the fault planes indicate N–S trending extension in the High Andes and Pacific Lowlands. The total amount of crustal stretching is small, probably of the order of 1% during the last 1–2 m.y. In the sub-Andes, folds and faults affecting Neogene and early Quaternary deposits result from N–S shortening. Nevertheless, it is supposed that this N-S shortening is of early quaternary age. The present-day compression probably strikes E-W, judging from focal mechanisms in the sub-Andes of central Peru, southern Bolivia, and northwest Argentina. Data from structural analysis of faults and from earthquake focal mechanisms allow us to surmise the state of stress in the Andes of southern Peru. The High Andes and Pacific Lowlands, subjected to N-S trending extension, are bounded by two zones of E-W trending compression: the sub-Andes to the east, and the contact between the convergent Nazca and South America plates to the west. In our model the maximum horizontal compressive stress trajectory σ Hmax is roughly parallel with the E-W convergence between the two plates; σ Hmax corresponds to σ 1, in the sub-Andes and to σ 2 in the High Andes. The latter situation is caused by the elevated mass of the High Andes, where σ zz (the vertical stress) is inferred to be σ 1. Thus the third principal stress axis, being orthogonal to the other two axes, it is oriented N-S, allowing extension to occur in that direction. On the other hand, in the sub-Andes σ zz is σ 3, and horizontal E-W shortening occurs. The state of stress in the Andean continental crust above the 30° dipping slab appears to be different from that in the Andes of Central Peru situated above the flat subducting segment. In this region, compressional deformantion affect a wider part of the Cordillera.

An active, deep marine strike-slip basin along the north anatolian fault in turkey

Abstract: The Tekirdag depression within the Marmara Sea in the Mediterranean region is an active, rhomb-shaped strike-slip basin along the North Anatolian fault with a basin floor at a water depth of −1150 m. New multichannel seismic reflection data and on-land geological studies indicate that the basin is forming along a releasing bend of the strike-slip fault and is filled with syntransform sediments of Pliocene-Quaternary age. The basin is bounded on one side by the North Anatolian fault and on the other side by a subparallel normal fault, which forms the steep submarine slope. In cross section the basin is strongly asymmetric with the thickness of the syntransform strata increasing from a few tens of meters on the submarine slope to over 2.5 km adjacent to the North Anatolian fault. Seismic sections also show that the slope-forming normal fault connects at depth to the North Anatolian fault, implying that the basin is completely detached from its substratum. The whole structure can be envisaged as a huge, rather flat, negative flower structure. The releasing bend of the North Anatolian fault, responsible for the formation of the basin, is flanked by a constraining bend. Along the constraining bend, the syntransform strata are being underthrust, implying a recent change in the direction of the regional displacement vector. This thrusting is responsible for the uplift of the submarine slope to a height of 924 m, possibly by a mechanism of elastic rebound. Regional geology suggests that most of the syntransform strata are lacustrine with only the topmost few hundred meters consisting of deep marine clays. The anomalous present depth of the Tekirdag depression is due to reduced Quaternary sedimentation coupled with high rates of displacement along the North Anatolian fault, which amounts to 20 mm/yr in the Marmara Sea region.

Fault Zone Architecture and Fluid Flow: Insights from Field Data and Numerical Modeling

Abstract: Fault zones in the upper crust are typically composed of complex fracture networks and discrete zones of comminuted and geochemically altered fault rocks. Determining the patterns and rates of fluid flow in these distinct structural discontinuities is a three-dimensional problem. A series of numerical simulations of fluid flow in a set of three-dimensional discrete fracture network models aids in identifying the primary controlling parameters of fault-related fluid flow, and their interactions, throughout episodic deformation. Four idealized, but geologically realistic, fault zone architectural models are based on fracture data collected along exposures of the Stillwater Fault Zone in Dixie Valley, Nevada and geometric data from a series of normal fault zones in east Greenland. The models are also constrained by an Andersonian model for mechanically compatible fracture networks associated with normal faulting. Fluid flow in individual fault zone components, such as a fault core and damage zone, and full outcrop scale model domains are simulated using a finite element routine. Permeability contrasts between components and permeability anisotropy within components are identified as the major controlling factors in fault-related fluid flow. Additionally, the structural and hydraulic variations in these components are also major controls of flow at the scale of the full model domains. The four models can also be viewed as a set of snapshots in the mechanical evolution of a single fault zone. Changes in the hydraulic parameters within the models mimic the evolution of the permeability structure of each model through a single deformation cycle. The model results demonstrate that small changes in the architecture and hydraulic parameters of individual fault zone components can have very large impacts, up to five orders of magnitude, on the permeability structure of the full model domains. Closure of fracture apertures in each fault zone magnifies the magnitude and orientation of permeability anisotropy in ways that are closely linked to the implicitly modeled deformation. Changes in fault zone architecture can cause major changes in permeability structure that, in turn, significantly impact the magnitude and patterns of fluid flux and solute transport both within and near the fault zone. Inferences derived from the model results are discussed in the context of the mechanical strength of an evolving fault zone, fault zone sealing mechanisms which control the conduit-barrier systematics of a fault zone as a flow system, and how these processes are related to fluid flow in natural fault zones.