Topic
Fault (geology)
About: Fault (geology) is a research topic. Over the lifetime, 26732 publications have been published within this topic receiving 744535 citations.
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TL;DR: In this article, a sequence of earthquakes occurred in close proximity to a well, which was being hydraulically fractured in southcentral Oklahoma, and was identified by cross correlating template waveforms from manually identified earthquakes.
Abstract: In January 2011, a sequence of earthquakes occurred in close proximity to a well, which was being hydraulically fractured in south‐central Oklahoma. The hydraulic fracturing of the Picket Unit B Well 4–18 occurred from 16 January 2011 18:43 through 22 January 16:54 UTC. This vertical well penetrated into the mature Eola‐Robberson oil field. Earthquakes were identified by cross correlating template waveforms from manually identified earthquakes and cross correlating these templates through the entire operation period of the Earthscope USArray Transportable Array (TA) station X34A. This produced a series of 116 earthquakes, which occurred from 17 January 2011 19:06 through 23 January 3:13 UTC with no other similar earthquakes identified at other times prior to or post‐hydraulic fracturing. The identified earthquakes range in local magnitude ( M L) from 0.6 to 2.9, with 16 earthquakes M L 2 or greater and a b ‐value of 0.98. There is a strong temporal correlation between hydraulic fracturing and earthquakes. This correlation is strengthened because hydraulic fracturing operations ceased for ∼2 days due to bad weather, and earthquakes can be observed to cease during this period and resume after hydraulic fracturing had resumed. Earthquakes were relocated using cross‐correlated phase arrivals and bootstrap iterations of hypoDD. Locations were well constrained for 86 earthquakes. These earthquake locations clearly delineate a fault which strikes ∼166°, subparallel to the mapped minor fault sets in the area, and dips steeply to the west. The earthquakes appear to have occurred at shallow depths from ∼2 to 3 km and within ∼2.5 km horizontally of the well. The first earthquake occurred ∼24 hrs after hydraulic fracturing began at the well. This delay is consistent with the diffusion of pore pressure in the subsurface over a distance of ∼2 km.
Online Material: Results from bootstrap hypoDD relocations using cross‐correlation phase arrivals.
239 citations
TL;DR: In this paper, the authors used 2D finite-difference ground-motion simulations to investigate the effect of the basin-edge structure in amplifying ground response in the 1994 Northridge earthquake.
Abstract: The 1994 Northridge earthquake produced ground motions in the northwest portion of the Los Angeles basin that were significantly larger than rock-site motions observed at locations just north of the basin. The Santa Monica area was hit particularly hard, with numerous structures being damaged or destroyed by the strong ground shaking. In this region, the basin-edge geology is controlled by the active strand of the east-west-striking Santa Monica fault, and virtually all of the structural damage occurred at or south of the fault location. We have used 2D finite-difference ground-motion simulations to investigate the effect of the basin-edge structure in amplifying ground response. Constraints on the basin-edge structure come from geologic cross sections, geophysical data, and seismological observations. Our simulations indicate that the shallow basin-edge structure (1 km deep) formed by the active strand of the Santa Monica fault creates a large amplification in motions immediately south of the fault scarp, in very good agreement with mainshock damage patterns, recorded ground motions, and locations of elevated site response. This large amplification results from constructive interference of direct waves with the basin-edge-generated surface waves and is quite similar to the basin-edge effect associated with the 1995 Kobe earthquake. In addition, we find that focusing effects created by the deeper basin structure (3 to 4 km deep) cannot explain the large motions observed immediately south of the fault scarp. This strongly suggests that the deep-basin focusing models proposed by Gao et al. (1996) and Alex and Olsen (1998) are not likely explanations of the observed pattern of ground-motion amplification in the Santa Monica area.
239 citations
TL;DR: In this article, the microstructure and petrophysical properties of fault rocks from siliciclastic hydrocarbon reservoirs of the North Sea are closely related to the effective stress, temperature and sediment composition at the time of deformation, as well as their post-deformation stress and temperature history.
Abstract: Abstract The microstructure and petrophysical properties of fault rocks from siliciclastic hydrocarbon reservoirs of the North Sea are closely related to the effective stress, temperature and sediment composition at the time of deformation, as well as their post-deformation stress and temperature history. Low permeability fault rocks may develop due to a combination of processes including: the deformation induced mixing of heterogeneously distributed fine-grained material (principally clays) with framework grains, pressure solution, cataclasis, clay smear, and cementation. Fault rocks can be classified into various types (disaggregation zones, phyllosilicate-framework fault rocks, cataclasites, clay smears, and cemented faults/fractures) based upon their clay and cement content as well as the amount of cataclasis experienced. In the absence of extensive cementation, the distribution of fault rock types along a fault plane can often be predicted from a detailed knowledge of the reservoir sedimentology. The permeability of fault rocks can vary by over six orders of magnitude, depending on the extent to which the porosity reduction processes have operated. Utilizing the strong link between the petrophysical properties of fault rocks and their geohistory allows the risks associated with fault seal evaluation to be reduced.
239 citations
TL;DR: In this paper, the authors show that the presence of serpentinite can reduce the integrated strength of the oceanic lithosphere by up to 30% and that if serpentinization is isolated to fault zones, strain localization should be enhanced, providing an explanation for variations in the style of normal faulting along slow-spreading ridge segments.
239 citations
TL;DR: The tensile source model generalizes the shear source model by assuming that the slip vector can be arbitrarily oriented with respect to the fault and is not constrained to lie within the fault plane.
Abstract: The tensile source model generalizes the shear source model by assuming that the slip vector can be arbitrarily oriented with respect to the fault and is not constrained to lie within the fault plane The proposed inversion for the parameters of tensile sources is based on the evaluation of the isotropic (ISO), compensated linear vector dipole (CLVD), and double-couple (DC) components in seismic moment tensors The most significant parameters inverted are the λ/μ ratio at the fault (denoted as the κ parameter) and the inclination α of the slip vector from the fault The κ parameter is significant for discriminating noisy moment tensors of shear earthquakes from those of tensile earthquakes The inclination α can be accurately determined from the DC component in the moment tensor because the DC component rapidly decreases with increasing α For example, the inclination of 20° causes DC being ∼50–60% only The inversion is applied to earthquakes which occurred in January 1997 in West Bohemia, Czech Republic It is shown that some of these earthquakes display tensile faulting The κ parameter is ∼01 The inclination of the slip from the fault attains values of up to 20° This inclination is a result of tensile traction and reduced shear traction along the fault and high-fluid pressure in the region
239 citations