bluuebunny/crossref_metadata_2025_split huggingface dataset:
Shear-wave anisotropy from dipole shear logs in oceanic crustal environments
Authors: Iturrino G. J. , Goldberg D. , Glassman H. , Patterson D. , Sun Y.-F. , Guerin G. , Haggas S. 
Published: April 2008

Abstract

The deployment of a down-hole dipole shear sonic tool in Hole 395A and Hole 735B marked the first two opportunities to measure high-resolution shear-wave velocity and

V
S

anisotropy profiles in oceanic crustal rocks. In Hole 395A near the Kane Fracture Zone, dipole sonic logs were recorded from 100–600 mbsf, and allow azimuthal anisotropy to be determined as a function of depth in the crust. The magnitude of

V
S

anisotropy varies with depth, from less than 3.2% in low-porosity flows at the bottom of the hole, to approximately 15.5% in highly fractured pillow basalts and breccias. The orientation of the fast

V
S

direction also varies over depth, with a mean value between 75°N and 80°E, and aligns with the strike of steeply dipping structures observed by down-hole electrical and acoustic images. This fast

V
S

angle orientation is locally oblique to the plate-spreading direction and to the Mid-Atlantic Ridge axis. In Hole 735B, drilled near the Atlantis Fracture Zone, dipole sonic logs from 23 to 596 mbsf indicate that

V
S

anisotropy varies with depth, with averages of 5.3% in the foliated and deformed gabbros recovered at the bottom of the hole; 4.5% in undeformed olivine and oxide-rich gabbros around 300 mbsf; and 6.8% in highly deformed mylonitic zones at shallow depths. The fast

V
S

angle also varies with depth, giving a mean orientation of approximately S45°E for well-resolved estimates in the upper interval of the hole. This direction aligns with the strike of steeply dipping fractures observed by down-hole imaging, and is locally oblique to the Southwest Indian ridge axis. Although the effects of regional stresses and local deformation of these holes may introduce anisotropy in the dipole sonic data, we conclude that crustal morphology in the vicinity of the holes contributes significantly to the magnitude and orientation of

V
S

anisotropy.
Electrical properties of slow-spreading ridge gabbros from ODP Hole 1105A, SW Indian Ridge
Authors: Einaudi F. , Pezard P. A. , Ildefonse B. , Glover P. 
Published: April 2008

Abstract
Physical properties of gabbroic samples from Ocean Drilling Program Hole 1105A were measured in the laboratory, with a particular emphasis on the analysis of electrical properties. This data-set includes the major lithologies sampled in ODP Hole 1105A: gabbros, olivine gabbros, oxide-rich gabbros, and, for all rock types, different ranges of alteration were sampled: from fresh to highly altered. All these lithologies correspond to the seismic Layer 3 layer of the oceanic crust, and large-scale geophysical data interpretation requires a complete understanding of the physical properties of rocks in this section. Electrical conductivities measured on brine-saturated gabbros reveal strong excess conductivity for samples rich in oxide minerals and, to a lesser extent, for altered samples. However, the classical models do not explain the excess conductivity reported in the oxide-rich samples when saturated with brine. The electrical conduction via electronic processes in metallic minerals has been taken into account in our analysis of the electrical properties. The oxide minerals’ contribution has been independently estimated through measuring dry electrical resistivity. These measurements allowed quantification of the electronic conduction, which can reach 80% of the full conductivity for the most oxide-rich gabbros.
Non-invasive characterization of fractured crystalline rocks using a combined multicomponent transient electromagnetic, resistivity and seismic approach
Authors: Meju M. A. 
Published: April 2008

Abstract

DC resistivity and seismic-refraction methods are well established in basement studies, and the multicomponent transient electromagnetic (TEM) method is also emerging as an effective tool for locating electrically conductive zones in crystalline rock underneath thick overburden. It can be expected that combining these three techniques will furnish a powerful non-invasive approach for characterizing fractured crystalline rocks. The aims of this paper are twofold, namely: (1) to establish the
in situ
geophysical signature of fracture-zones in weathered crystalline rock masses using the TEM profiling method, and (2) determine the resistivity and seismic-velocity relationship in the zones of fractured crystalline rock evinced by TEM profiling. Multicomponent TEM data from terrains with varying degrees of weathering are examined in this paper. The TEM response over a deeply weathered fracture zone in granite is found to be band-limited, with a consistent pattern of vertical voltage response (
V
z
) at early times enabling accurate location of the wet fracture zone which manifests as a steep conductive feature in 2D DC resistivity imaging. Depending on the thickness of the weathered mantle and the measurement bandwidth, the composite
V
z
signature consists of three parts: a high amplitude response with a single peak centred on the target fracture zone at very early times; a near invariant or slowly decreasing amplitude response across the fracture zone at some intermediate time; and a marked low-amplitude response at the centre of the fracture zone with higher amplitudes near the flanks (i.e. twin peaks) at later times. The across-strike voltage response (
V
x
) is diagnostic of conductive fracture zones and exhibits a marked sign reversal. The result of 2D inversion of resistivity, magnetotelluric and seismic-refraction recordings over an intensively fractured granodiorite suggests that resistivity (ρ) and compressional-wave velocity (
V
P
) can be related in the form log
10
ρ = m log
10
V
P
+
c
, where
m
and
c
are constants.
Non-linearity in multidirectional P-wave velocity: confining pressure behaviour based on real 3D laboratory measurements, and its mathematical approximation
Authors: Přikryl R. , Klíma Karel , Lokajíček T. , Pros Z. 
Published: April 2008

Abstract
Experimental laboratory measurements of P-wave velocity confirm the superposition of linearity over non-linearity by a progressive increase in confining pressure. The increase in confining pressure diminishes the influence of microcracks that are partly or totally closed. At a certain stress level, the trend of P-wave velocity with applied confining pressure approaches that of a solid without cracks, and a linear increase in elastic wave velocity occurs under high confinement.

Several studies have focused on the problem of mathematical approximation of this phenomenon (Carlson & Gangi 1985; Wepfer & Christensen 1991; Greenfield & Graham 1996; Meglis
et al.
1996). Although successful within a certain degree of error, they provide neither a multidirectional solution nor the comparison of results with rock fabric. In this study, an analytical relation was applied to describe the P-wave velocity-confining pressure behaviour of quasi-isotropic rocks (granites) and their anisotropic equivalents (orthogneisses). Two parameters of this relationship reflect the elastic properties of the rock matrix, and two others are related to the presence of microcracks, their density and genesis. The results of a mathematical approximation of the P-wave velocity-confining pressure behaviour show a favourable correlation to the measured data-sets. Comparison of individual fitted parameters with the rock fabric provides an improved understanding of the material’s mechanical behaviour.
The
14
C-polymethylmethacrylate (PMMA) impregnation method and image analysis as a tool for porosity characterization of rock-forming minerals
Authors: Oila E. , Sardini P. , Siitari-Kauppi M. , Hellmuth K.-H. 
Published: April 2008

Abstract

Accurate knowledge of porosity is essential for understanding the links between basic petrophysical parameters, such as diffusion coefficients, permeability and conductivity. Standard methods used to determine porosity quantify the bulk porosity and the distribution of pore sizes. Crystalline rocks are rarely monomineralic, and the porosity of polyphasic rocks is considered heterogeneous at the mineral grain scale. Calculation of bulk petrophysical parameters must take into account porosity and mineral-phase microstructures, as well as connectivity. The polymethylmethacrylate (PMMA) method uses radioactively (
14
C)-labelled methylmethacrylate (
14
C-MMA) liquid to impregnate the rock sample, which is then polymerized by irradiation, cut and autoradiographed. Porosity is quantified by digitizing the autoradiograph and subsequent densitometry. Staining of the same rock surface uses chemical agents that rapidly reveal the primary minerals of unaltered and altered crystalline rocks: mainly quartz, K-feldspar, plagioclase and dark minerals. The images of PMMA autoradiographs and stained rock surfaces are combined to quantify mineral-specific porosities.

The methodology has been applied here to a granite core from Palmottu (central Finland) representing coarse-grained granite adjacent to a potential water-conducting fracture. Imaging of the porosity relative to mineralogy is presented and complemented by mineral specific porosities.
Interactions between glaciers and permafrost: an introduction
Authors: Harris Charles , Murton Julian B. 
Published: April 2008

Abstract
A consideration of the interactions between glaciers and permafrost is essential to many environmental studies of cold regions. This paper reviews how concepts, field data and experimental studies from glaciology and geocryology can provide a basis for improved understanding of some of the key glacier-permafrost interactions at scales ranging from continental ice sheets to small proglacial streams. Glacitectonic processes are strongly influenced by water pressures beneath subglacial and proglacial permafrost, and by the amount of unfrozen water within the permafrost. Burial of glacier ice and growth of intrasedimental ice also occur within sub- and proglacial permafrost, and together they produce a complex assemblage of ground ice in glaciated frozen lowlands. In mountain regions, rock glaciers are associated with the presence of ground ice, and represent a landform that stradles the semantic fence separating glacial features from permafrost features. In proglacial and ice-marginal environments, geomorphological activity reflects the combined effects of glacially- and periglacially-conditioned processes operating synchronously in adjacent areas, or in succession; such activity includes the transport of sediment in glacierized catchments and the calving of glacial ice in ice-marginal lakes. Interaction between permafrost and glacial phenomena depends largely on their proximity: where permafrost occurs close to glaciers, the thermal regime of the active layer is influenced in part by the surface covering of adjacent glacial ice through its effect on albedo and ground heat flux. Glacier-permafrost interactions are particularly important in recently deglaciated terrain, where permafrost may be aggrading. This ‘paraglacial’ zone often shows rapid geomorphological change. Thus, glacier-permafrost interactions are complex and occur over a wide range of temporal and spatial scales.
The interaction of a surging glacier with a seasonally frozen foreland: Hagafellsjökull-Eystri, Iceland
Authors: Bennett Matthew R. , Huddart David , Waller Richard I. 
Published: April 2008

Abstract
This paper describes aspects of the landform-sediment assemblage produced by a recent surge of Hagafellsjökull-Eystri. This surge occurred during the winter and early spring of 1998/1999 and consequently advanced into a partially frozen foreland. Two aspects of this landform-sediment assemblage are considered. First the evidence for a frozen subglacial sediment layer beneath a lateral piedmont lobe formed during the surge is reviewed. This sediment layer consists of blocks of glacier ice set within a matrix of frozen sediment and was injected into basal crevasses to form a network of crevasse-squeeze ridges prior to freezing. The sediment layer appears to provide evidence of subfreezing deformation at the termination of the surge. Secondly the paper examines the detailed tectonic facies within a push-moraine formed along the eastern latero-frontal margin of the glacier during the surge. Architecturally this push moraine consists of a multi-layered slab of glaciofluvial sediments with a monocline structure that has been displaced laterally by the advancing ice margin. The sediment slabs within this monocline are characterized by both brittle and ductile styles of deformation. The authors argue that the observed variation in deformation style may be explained by spatial variation in the extent to which the glacial foreland was frozen or unfrozen at the time of displacement. Areas of frozen foreland would have behaved in a brittle fashion, while unfrozen areas deformed in a more ductile manor. Both these aspects of the landform-sediment assemblage examined in this paper appear to be the product of the seasonal timing of the surge. Not only do they add to our understanding of surge-type landsystems, but they also illustrate the potential of winter advances around the margins of some temperate glaciers to explore the coupling between glaciers and frozen proglacial sediments.
Glacier-permafrost hydrological interconnectivity: Stagnation Glacier, Bylot Island, Canada
Authors: Moorman Brian J. 
Published: April 2008

Abstract
The complex thermal structure in areas where polythermal glaciers and continuous permafrost are present increases the potential for direct linkages between subsurface water conduits within glaciers and permafrost. In this study, hydrologic features of a glacier and the surrounding ice-cored moraines were examined and the potential for englacial water to flow out of the glacier and into the moraine was investigated. Ground-penetrating radar investigations, dye trace tests and direct observations of hydrological features (e.g., moulins, springs and caves) on and around Stagnation Glacier on Bylot Island, Arctic Canada, were undertaken. Data reveal that englacial conduits extend from the glacier into the adjacent ice-cored moraine. Glacial meltwater may have experienced variable flow conditions over the last 10 years and the conduit closures have occurred over a much longer time period. The study illustrates the interconnectivity of the glacial and permafrost hydrological systems.
Cryological processes implied in Arctic proglacial stream sediment dynamics using principal components analysis and regression
Authors: Irvine-Fynn T. D. L. , Moorman B. J. , Sjogren D. B. , Walter F. S. A. , Willis I. C. , Hodson A. J. , Williams J. L. M. , Mumford P. N. 
Published: April 2008

Abstract
In high latitudes, recent research has demonstrated that both thermo-erosion and temperature dependence influence sediment release into fluvial systems. An analysis of proglacial suspended sediment concentration (SSC) dynamics is presented for three glacierized basins: cold-based Austre Brøggerbreen (Svalbard), polythermal Midre Lovénbreen (Svalbard) and polythermal Glacier B28 (Bylot Island). The temporal variation in processes dominating SSC patterns is assessed using stepwise multivariate regression following the subdivision of the time series. Partitioning of the time series is achieved through principal components and change point analyses. The regression models use discharge and surrogate predictor variables to model SSC, while improvements are made by using air temperature and radiation terms as independent variables. Comparisons are drawn between two sets of models with contrasting subseasonal division. By interpretation of the regression model characteristics, temporal changes in physical processes are implied over the course of the time periods. Numerical analyses suggest there is a trend for changes between fluvial, glacial and periglacial factors forcing responses in SSC. Therefore, it is conjectured that glaciofluvial sediment transfer at high latitudes is influenced by periglacial processes and conditions. This has implications for the predictions of fluvial sediment loads in a changing environment, and the use of sedimentary records for environmental reconstruction.
Late Holocene solifluction history reconstructed using tephrochronology
Authors: Kirkbride Martin P. , Dugmore Andrew J. 
Published: April 2008

Abstract

Phases of activity of four solifluction lobes at an altitude of 750–800 m are dated by tephrochronology at Snaefell, central eastern Iceland (64°48′ N 15°33′ E). The sample includes sorted lobes with tread gradients of 3–11° and unsorted (turf-banked terraces) in slope-foot locations. Trenches through lobe fronts reveal detailed internal structures picked out by multiple tephra layers. The tephras V1717, V1477, Ö1362, V870, Hekla-3 (2900 years
bp
and Hekla-4 (3800 years
bp
) provide isochronous surfaces of known age whose deformation and disturbance indicate mass movement and/or cryoturbation of the soil cover. Undisturbed soil including the Hekla-3 tephra indicates an absence of solifluction prior to 2900 years
bp
. Several centuries after Hekla-3, gravel-rich horizons mark wide-spread frost heave and solifluction of hillslopes. Later stabilization of these lobes allowed the accumulation of aprons of aeolian sediment below lee-side risers. These aprons contain
in situ
mediaeval tephras, dating the inception of solifluction to a considerable time prior to Norse settlement. The likely period of this first phase of solifluction is the Later Bog Period of the Subatlantic,
c.
2500-1000 years
bp
. The aprons are currently being overridden and deformed by solifluction lobes reactivated in the Little Ice Age.
Segmentation and interaction of normal faults within the Colfiorito fault system (central Italy)
Authors: Mirabella F. , Boccali V. , Barchi M. R. 
Published: April 2008

Abstract
Fault segments belonging to a fault population can link and interact, eventually forming a single larger fault, and thus affecting the estimation of the maximum expected earthquake. We present throw distribution data along the Quaternary normal faults of the Colfiorito fault system (central Italy), which consists of four main fault segments and where a seismic sequence occurred in 1997–1998. Throw values along the two central overlapping, en-échelon segments (8.5–9.5 km long) were measured on a good stratigraphic marker, by constructing a set of closely spaced geological cross-sections, perpendicular to the fault strike. As these faults are commonly retained active and border Quaternary basins, we compare morphological and geological throws in order to verify the faults neotectonic activity. Geological and morphological throw distributions show good correlation, testifying that recent faulting affected the topographic surface and suggesting that the observed offset completely accumulated during the Quaternary. The throw distribution along the fault segments is asymmetric and reaches maximum values (500–550 m) within the zone of fault overlap, suggesting mechanical interaction between the studied faults. Maximum length-throw correlation suggests that the studied faults grew according to a linear scaling relationship.
Textural controls on the brittle deformation of dolomite: variations in peak strength
Authors: Austin N. J. , Kennedy L. A. 
Published: April 2008

Abstract

Textural controls on the peak strength of dolomite are investigated through 23 triaxial deformation experiments, performed at confining pressures of 25, 50, and 100 MPa on texturally diverse dolomites. The mechanical data from these experiments are fit to an empirical failure criterion to elucidate the most significant parameters in dictating the peak strength of dolomite. Neither grain size nor porosity is required to quantitatively predict the peak strength of dolomite. Instead, only the effective Young’s modulus, and the empirically predicted uniaxial compressive strength, along with experimentally controlled confining pressure, are required in order to explain the peak strength to and
R
2
better than 0.89. A Hall-Petch relationship does not apply to this data set as a consequence of the variability in intragranular and grain boundary textures, which appear to overshadow the role of grain size. It is, therefore, essential that grain boundary textures and intragranular flaws be examined prior to making predictions regarding the relative peak strengths of chemically and mineralogically similar dolomites.
Textural controls on the brittle deformation of dolomite: the transition from brittle faulting to cataclastic flow
Authors: Austin N. J. , Kennedy L. A. , Logan J. M. , Rodway R. 
Published: April 2008

Abstract

To investigate the role of texture on the brittle deformation of dolomite, 23 triaxial deformation experiments were performed at confining pressures of 25, 50, and 100 MPa, dry, at room temperature, on dolomite from three texturally distinct sample suites. The variations in the mechanical response of these mineralogically and chemically similar dolomites, and the ensuing microstructures, indicate that grain boundary textures promote or inhibit the ability of grains to shear and rotate with respect to one another, whereas the presence of intragranular flaws, such as cleavage, that act as weaknesses, promote intragranular deformation. In samples with porosities greater than
c.
7%, inelastic pore collapse controls the transition from brittle faulting to extensive intragranular deformation and cataclastic flow. This porosity is much higher than has been observed at the onset of pore collapse in calcite, as a consequence of the inability of dolomite to deform by crystal plastic processes at room temperature. Combined, these textural features may dictate the transition from brittle faulting to cataclastic flow in brittle rocks in the upper crust.
Stress-strain rate history of a midcrustal shear zone and the onset of brittle deformation inferred from quartz recrystallized grain size
Authors: Gueydan F. , Mehl C. , Parra T. 
Published: April 2008

Abstract

The quantification of quartz shear stress and strain rate within a midcrustal shear zone provides a mechanical frame to describe the evolution from penetrative ductile deformation to localized deformation and the onset of brittle deformation. The quantification is based on the relationships between the quartz recrystallized grain size, the quartz shear stress (piezometric relation) and the strain rate (dislocation creep flow law). Increasing strain is accompanied by a general decrease of quartz recrystallized grain size and a decrease in grain size scattering. These are interpreted as a result of a complex loading history. The evolution from penetrative ductile deformation toward strain localization, marked by an increase of the strain rate by one order of magnitude, is inferred from grain size memory. Brittle deformation is triggered for quartz shear stress of the order of 70 MPa and strain rate close to 10
−12
s
−1
. This relative low value of the quartz shear stress necessary to trigger faulting implies a less important strength for the midcrust compared with strengths predicted by classical rheological envelopes.