84 research outputs found
Simulating spatial and temporal evolution of multiple wing cracks around faults in crystalline basement rocks
Fault zones are structurally highly spatially heterogeneous and hence extremely complex. Observations of fluid flow through fault zones over several scales show that this structural complexity is reflected in the hydrogeological properties of faults. Information on faults at depth is scarce, hence, it is highly valuable to understand the controls on spatial and temporal fault zone development. In this paper we increase our understanding of fault damage zone development in crystalline rocks by dynamically simulating the growth of single and multiple splay fractures produced from failure on a pre-existing fault. We present a new simulation model, MOPEDZ (Modeling Of Permeability Evolution in the Damage Zone surrounding faults), that simulates fault evolution through solution of Navier's equation with a combined Mohr-Coulomb and tensile failure criteria. Simulations suggest that location, frequency, mode of failure and orientation of splay fractures are significantly affected both by the orientation of the fault with respect to the maximum principal compressive stress and the conditions of differential stress. Model predictions compare well with published field outcrop data, confirming that this model produces realistic damage zone geometries
Phase diagram of the anti-ferromagnetic xxz model in the presence of an external magnetic field
The anisotropic s=1/2 anti-ferromagnetic Heisenberg chain in the presence of
an external magnetic field is studied by using the standard quantum
renormalization group. We obtain the critical line of the transition from
partially magnetized (PM) phase to the saturated ferromagnetic (SFM) phase. The
crossover exponent between the PM phase and anti-ferromagnetic Ising (AFI)
phase is evaluated. Our results show that the anisotropy(\d) term is relevant
and causes crossover. These results indicate that the standard RG approach
yields fairly good values for the critical points and their exponents. The
magnetization curve, correlation functions and the ground state energy per site
are obtained and compared with the known exact results.Comment: A LaTex file(20 pages) and 9 PS figure
Observational and theoretical evidence for frictional-viscous flow at shallow crustal levels
Along the Hikurangi Subduction Margin, accretionary prism uplift has exposed the Hungaroa fault zone, an inactive thrust developed within the Middle to Late Eocene Wanstead Formation. Within the ~33 m-wide fault core, deformation of the smectitic, calcareous mudstone matrix produced a penetrative foliation that locally wraps around clasts. Deformation occurred at temperatures constrained by syntectonic calcite vein clumped isotope thermometry, which yielded a narrow range of Î47 values between 0.445 ± 0.024â° and 0.482 ± 0.013â°, corresponding to a mean calcite precipitation temperature of 82â12+13 °C. Optical and scanning electron microscopy analyses reveal that calcite underwent: dissolution along stylolites and clast, vein, and microlithon margins; precipitation in foliation-parallel and foliation-perpendicular extension veins; and precipitation in hybrid veins and strain fringes. Maximum differential stress estimates obtained from calcite twin densities (44.1 ± 13.9 to 96.6 ± 20.8 MPa) are consistent with those sustainable by a cohesionless fault at ~3 km depth with a friction coefficient in the range measured for two calcareous mudstones (ÎŒ = 0.38 to 0.50) and a micrite clast (ÎŒ = 0.61 and 0.64). Marlstone clasts within the foliated calcareous mudstone matrix contain mutually cross-cutting shear fractures and extension veins with crack-seal textures, providing evidence for temporal fluctuations in shear strength resulting from pore fluid overpressure transients. At strain rates imposed during laboratory experiments, frictional sliding involves granular flow processes. Yet, calcite microstructures indicate that diffusive mass transfer played an important role in accommodating deformation. We model the fault zone rheology assuming diffusion-controlled frictional-viscous flow, with deformation at strain rates γˆ10â9 sâ1 able to have taken place at very low shear stresses (Ï < 10 MPa) given sufficiently short diffusion distances (d < 0.1 mm), even in the absence of pore fluid overpressures. However, if grain-scale and fracture-scale processes change the diffusion distance, fault zones deforming via frictional-viscous flow can exhibit temporally variable strain rates. Thus, our results suggest that the shallow (up-dip) limit of the seismogenic zone is not a simple function of temperature in fault zones governed by a frictional-viscous flow rheology
High Precision Renormalization Group Study of the Roughening Transition
We confirm the Kosterlitz-Thouless scenario of the roughening transition for
three different Solid-On-Solid models: the Discrete Gaussian model, the
Absolute-Value-Solid-On-Solid model and the dual transform of the XY model with
standard (cosine) action. The method is based on a matching of the
renormalization group flow of the candidate models with the flow of a bona fide
KT model, the exactly solvable BCSOS model. The Monte Carlo simulations are
performed using efficient cluster algorithms. We obtain high precision
estimates for the critical couplings and other non-universal quantities. For
the XY model with cosine action our critical coupling estimate is
. For the roughening coupling of the Discrete Gaussian
and the Absolute-Value-Solid-On-Solid model we find and
, respectively.Comment: 46 pages, PostScript file (compressed and uuencoded), preprints
CERN-TH.7182/94, HU-RI-2/94, and MS-TPI-94-
Motor coordination problems in children and adolescents with ADHD rated by parents and teachers: effects of age and gender
Summary.
Objective. ADHD is frequently accompanied by motor coordination problems. However, the co-occurrence of poor motor performance has
received less attention in research than other coexisting problems in ADHD. The underlying mechanisms of this association
remain unclear. Therefore, we investigated the prevalence of motor coordination problems in a large sample of children with
ADHD, and the relationship between motor coordination problems and inattentive and hyperactive/impulsive symptoms. Furthermore,
we assessed whether the association between ADHD and motor coordination problems was comparable across ages and was similar
for both genders.
Method. We investigated 486 children with ADHD and 269 normal controls. Motor coordination problems were rated by parents (Developmental
Coordination Disorder Questionnaire) and teachers (Groningen Motor Observation Scale).
Results. Parents and teachers reported motor coordination problems in about one third of children with ADHD. Problems of fine and
gross motor skills, coordination skills and motor control were all related to inattentive rather than hyperactive/impulsive
symptoms. Relative to controls, motor coordination problems in ADHD were still present in teenagers according to parents;
the prevalence diminished somewhat according to teachers. Boys and girls with ADHD were comparably affected, but motor performance
in controls was better in girls than in boys.
Conclusions. Motor coordination problems were reported in one third of children with ADHD and affected both boys and girls. These problems
were also apparent in adolescents with ADHD. Clinicians treating children with ADHD should pay attention to co-occurring motor
coordination problems because of the high prevalence and the negative impact of motor coordination problems on daily life
Large-scale analyses of common and rare variants identify 12 new loci associated with atrial fibrillation
Atrial fibrillation affects more than 33 million people worldwide and increases the risk of stroke, heart failure, and death. Fourteen genetic loci have been associated with atrial fibrillation in European and Asian ancestry groups. To further define the genetic basis of atrial fibrillation, we performed large-scale, trans-ancestry meta-analyses of common and rare variant association studies. The genome-wide association studies (GWAS) included 17,931 individuals with atrial fibrillation and 115,142 referents; the exome-wide association studies (ExWAS) and rare variant association studies (RVAS) involved 22,346 cases and 132,086 referents. We identified 12 new genetic loci that exceeded genome-wide significance, implicating genes involved in cardiac electrical and structural remodeling. Our results nearly double the number of known genetic loci for atrial fibrillation, provide insights into the molecular basis of atrial fibrillation, and may facilitate the identification of new potential targets for drug discovery
Multi-ethnic genome-wide association study for atrial fibrillation
Atrial fibrillation (AF) affects more than 33 million individuals worldwide and has a complex heritability. We conducted the largest meta-analysis of genome-wide association studies (GWAS) for AF to date, consisting of more than half a million individuals, including 65,446 with AF. In total, we identified 97 loci significantly associated with AF, including 67 that were novel in a combined-ancestry analysis, and 3 that were novel in a European-specific analysis. We sought to identify AF-associated genes at the GWAS loci by performing RNA-sequencing and expression quantitative trait locus analyses in 101 left atrial samples, the most relevant tissue for AF. We also performed transcriptome-wide analyses that identified 57 AF-associated genes, 42 of which overlap with GWAS loci. The identified loci implicate genes enriched within cardiac developmental, electrophysiological, contractile and structural pathways. These results extend our understanding of the biological pathways underlying AF and may facilitate the development of therapeutics for AF
Bedrock geology of DFDP-2B, central Alpine Fault, New Zealand
<p>During the second phase of the Alpine Fault, Deep Fault Drilling Project (DFDP) in the Whataroa River, South Westland, New Zealand, bedrock was encountered in the DFDP-2B borehole from 238.5â893.2â
m Measured Depth (MD). Continuous sampling and meso- to microscale characterisation of whole rock cuttings established that, in sequence, the borehole sampled amphibolite facies, Torlesse Composite Terrane-derived schists, protomylonites and mylonites, terminating 200â400â
m above an Alpine Fault Principal Slip Zone (PSZ) with a maximum dip of 62°. The most diagnostic structural features of increasing PSZ proximity were the occurrence of shear bands and reduction in mean quartz grain sizes. A change in composition to greater mica:quartzâ+âfeldspar, most markedly below c. 700â
m MD, is inferred to result from either heterogeneous sampling or a change in lithology related to alteration. Major oxide variations suggest the fault-proximal Alpine Fault alteration zone, as previously defined in DFDP-1 core, was not sampled.</p
Petrophysical, Geochemical, and Hydrological Evidence for Extensive Fracture-Mediated Fluid and Heat Transport in the Alpine Fault's Hanging-Wall Damage Zone
International audienceFault rock assemblages reflect interaction between deformation, stress, temperature, fluid, and chemical regimes on distinct spatial and temporal scales at various positions in the crust. Here we interpret measurements made in the hangingâwall of the Alpine Fault during the second stage of the Deep Fault Drilling Project (DFDPâ2). We present observational evidence for extensive fracturing and high hangingâwall hydraulic conductivity (âŒ10â9 to 10â7 m/s, corresponding to permeability of âŒ10â16 to 10â14 m2) extending several hundred meters from the fault's principal slip zone. Mud losses, gas chemistry anomalies, and petrophysical data indicate that a subset of fractures intersected by the borehole are capable of transmitting fluid volumes of several cubic meters on time scales of hours. DFDPâ2 observations and other data suggest that this hydrogeologically active portion of the fault zone in the hangingâwall is several kilometers wide in the uppermost crust. This finding is consistent with numerical models of earthquake rupture and offâfault damage. We conclude that the mechanically and hydrogeologically active part of the Alpine Fault is a more dynamic and extensive feature than commonly described in models based on exhumed faults. We propose that the hydrogeologically active damage zone of the Alpine Fault and other large active faults in areas of high topographic relief can be subdivided into an inner zone in which damage is controlled principally by earthquake rupture processes and an outer zone in which damage reflects coseismic shaking, strain accumulation and release on interseismic timescales, and inherited fracturing related to exhumation
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