Fault (geology)

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

Collateral damage: Evolution with displacement of fracture distribution and secondary fault strands in fault damage zones

Abstract: resulting in an apparently more gradual decay with distance, and (3) a change in apparent decay and fault zone thickness becomes evident in faults that have displaced more than ∼150 m. This last observation is consistent with a stochastic model where strand formation is related to the number of fractures within the damage zone, which in turn is a function of displacement. These three observations together suggest that the apparent break in scaling between small and large faults is due to the nucleation of secondary faults and not a change in process.

Earthquake slip weakening and asperities explained by thermal pressurization

Abstract: An earthquake occurs when a fault weakens during the early portion of its slip at a faster rate than the release of tectonic stress driving the fault motion. This slip weakening occurs over a critical distance, D(c). Understanding the controls on D(c) in nature is severely limited, however, because the physical mechanism of weakening is unconstrained. Conventional friction experiments, typically conducted at slow slip rates and small displacements, have obtained D(c) values that are orders of magnitude lower than values estimated from modelling seismological data for natural earthquakes. Here we present data on fluid transport properties of slip zone rocks and on the slip zone width in the centre of the Median Tectonic Line fault zone, Japan. We show that the discrepancy between laboratory and seismological results can be resolved if thermal pressurization of the pore fluid is the slip-weakening mechanism. Our analysis indicates that a planar fault segment with an impermeable and narrow slip zone will become very unstable during slip and is likely to be the site of a seismic asperity.

The structural evolution of the northern Viking Graben and its bearing upon extensional modes of basin formation

Abstract: Recent advances in the understanding of rift basin formation, coupled with the increasing public availability of seismic and well data across the northern Viking Graben (60–61°N), have enabled a detailed analysis of its development. Two rifting episodes can be recognized: ?Late Permian–early Triassic and Bathonian–Ryazanian. Major regional unconformities, thought to be primarily tectonic rather than eustatic in origin, separate and subdivide the rifting episodes. The earlier episode involved extension about a N–S axis; ensuing (Triassic–Mid-Jurassic) thermal subsidence was accommodated on steep faults. During the later episode a new NE–SW fault trend was superimposed on pre-existing patterns. Major block rotation, marking active rifting, ceased at the end of the Ryazanian. During the second post-rift episode there was a progressive migration of active faulting towards the basin margins and, as a result, a widening-with-time of the area undergoing subsidence. Asymmetric subsidence of the central part of the basin was hinged at the western margin of the Horda Platform, and accommodated to the NW on major faults within the Tampen Spur, β factors, for the second rifting episode were calculated both by relating subsidence to extension, and by measuring observed extension. Values calculated by both methods increase consistently towards the basin axis for both rifting and thermal subsidence phases, but are greater for the latter phase. Subsidence patterns are similar for both rifting and thermal subsidence episodes, so that there is vertical stacking of relatively thick sequences in the axis of the northern Viking Graben. These factors preclude the application of models involving uniform and non-uniform stretching and also preclude oblique extension; depth-dependent stretching is preferred.

Dike‐induced faulting and graben subsidence in volcanic rift zones

Abstract: Field observations and geodetic data indicate that dike intrusion in volcanic rift zones typically generates normal faulting and graben subsidence at the Earth's surface. Elastic models indicate that two-dimensional (infinite strike length) dikes do not lower the ground surface above the dike and that normal faults do not lower the surface significantly, more than one down-dip fault length from the fault trace. Dikes of finite length produce subsidence above the dike, but not by an appreciable amount, for appropriate dike lengths. Therefore the observed graben subsidence can be achieved only if fault slip extends virtually to the dike plane at depth. Dike intrusion increases the horizontal compression adjacent to the dike and decreases the compression beyond the dike perimeter. Therefore fault slip extending to the dike plane is most likely to occur above or in front of the laterally propagating dike. Two data sets documenting the change in surface elevation accompanying dike intrusion in the Krafla rift zone, Iceland, were inverted to determine the dike and fault geometry at depth. Ten kilometers south of the Krafla caldera, subsidence of a graben 1.5 km wide was produced by fault slip to 1.5–2 km depth, essentially to the dike top. Forty kilometers north of the caldera, subsidence of a graben 6 km wide was produced by fault slip to 4–5 km depth, well within the zone of compression adjacent to the dike. In order to determine if fault slip in front of the dike could have produced the observed subsidence north of the caldera, a three-dimensional boundary element model that computes fault slip during lateral dike propagation was developed. Results indicate that fault slip in front of the dike is capable of producing most of the subsidence observed. Additional subsidence could result from reasonable mechanical anisotropy of the rift zone. The lack of deep fault slip south of the caldera is attributed to a less favorable initial stress state. This is consistent with differences in the tectonic history of the two regions over the past several centuries.