Fault (geology)

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

Implications of deformation following the 2002 Denali, Alaska, earthquake for postseismic relaxation processes and lithospheric rheology

Abstract: [1] During the first 2 years following the 2002 Mw = 7.9 Denali, Alaska, strike-slip earthquake, a large array of Global Positioning System (GPS) receivers recorded rapid postseismic surface motions extending at least 300 km from the rupture and at rates of more than 100 mm/yr in the near field. Here we use three-dimensional (3-D) viscoelastic finite element models to infer the mechanisms responsible for these postseismic observations. We consider afterslip both from an inversion of GPS displacements and from stress-driven forward models, poroelastic rebound, and viscoelastic flow in the lower crust and upper mantle. Several conclusions can be drawn: (1) No single mechanism can explain the postseismic observations. (2) Significant postseismic flow below a depth of 60 km is required to explain observed far-field motions, best explained by a weak upper mantle with a depth-dependent effective viscosity that ranges from >1019 Pa s at the Moho (50 km depth) to 3–4 × 1018 Pa s at 100 km depth. (3) Shallow afterslip within the upper crust occurs adjacent to and beneath the regions of largest coseismic slip. (4) There is a contribution from deformation in the middle and lower crust from either lower crustal flow or stress-driven slip. Afterslip is preferred over broad viscoelastic flow owing to the existence of seismic velocity discontinuities across the fault at depth, though our modeling does not favor either mechanism. If the process is viscoelastic relaxation, the viscosity is a factor of 3 greater than the inferred mantle viscosity. (5) Poroelastic rebound probably contributed to the observed postseismic deformation in the immediate vicinity of the Denali/Totschunda junction. These conclusions lead us to infer an Alaskan mechanical lithosphere that is about 60 km thick, overlying a weak asthenosphere, and a Denali fault that cuts through the entire lithosphere with shear accommodated by faulting in the top ∼20 km and time-dependent aseismic shear below.

Tectonics of the Najd Transcurrent Fault System, Saudi Arabia

Abstract: The Najd Belt is a major transcurrent (strike-slip) fault system of Proterozoic age in the Arabian Shield. The belt is a braided complex of parallel and curved, en echelon faults. Complex arrays of secondary structures including strike-slip, oblique-slip, thrust and normal faults, together with folds and dyke swarms are associated with some major faults, particularly near their terminations. The secondary structures indicate that compressional and extensional/dilational conditions existed synchronously in different parts of the fault zone. The outcrop traces of faults and syn tectonic dykes are used to interpret the configuration of principal compressive stresses during formation of parts of the secondary fracture systems. Second order deformation was a series of separate events in a complex episodic faulting history. Comparison with model studies indicates that master faults extended in length in stages and periodically developed arrays of secondary structures. Propagation of the major faults took place along splay trajectories which inter-connected to form a sub-parallel sheeted and braided zone. Interpretation of the aeromagnetic maps indicates that the Najd Belt is broader at depth than the outcropping fault complex, and that more continuous structures underlie arrays of faults at surface. The fault pattern is mechanically explicable in terms of simple shear between rigid blocks beneath the exposed structures.

The kinematics of a transition from subduction to strike‐slip: An example from the central New Zealand plate boundary

Abstract: [1] We develop a kinematic model for the transition from subduction beneath the North Island, New Zealand, to strike-slip in the South Island, constrained by GPS velocities and active fault slip data To interpret these data, we use an approach that inverts the kinematic data for poles of rotation of tectonic blocks and the degree of interseismic coupling on faults in the region Convergence related to the Hikurangi subduction margin becomes very low offshore of the northern South Island, indicating that in this region the majority of the relative plate motion has been transferred onto faults within the upper plate, as suggested by previous studies This result has implications for understanding the likely extent of subduction interface earthquake rupture in central New Zealand Easterly trending strike slip faults (such as the Boo Boo fault) are the key features that facilitate the transfer of strike-slip motion from the northern South Island faults further north into the southern North Island and onto the Hikurangi subduction thrust Our results also indicate that the transition from rapid forearc rotation adjacent to the Hikurangi subduction margin to a strike-slip dominated plate boundary (with negligible vertical-axis rotation) in the South Island occurs via a crustal-scale hinge or kink in the upper plate, compatible with paleomagnetic and structural geological data Despite the ongoing tectonic evolution of the central New Zealand region, our study highlights a remarkable consistency between data sets spanning decades (GPS), thousands of years (active faulting data), and millions of years (paleomagnetic data and bedrock structure)