A review of electromagnetic investigations in the Kapuskasing uplift and surrounding regions: electrical properties of key rocks

1994 ◽  
Vol 31 (7) ◽  
pp. 1042-1051 ◽  
Author(s):  
Marianne Mareschal ◽  
Ron D. Kurtz ◽  
Richard C. Bailey
Keyword(s):  
Grain Boundaries ◽  
Upper Mantle ◽  
Field Measurements ◽  
Surface Expression ◽  
High Grade ◽  
Near Surface ◽  
Solid Films ◽  
Conductivity Structure ◽  
Mantle Conductivity ◽  
Detachment Zone

Electromagnetic investigations of the Kapuskasing uplift show that the gross electrical conductivity structure of the present crust is subhorizontal (contrary to the lithology as defined by seismic experiments), with increasing conductivity with depth, a feature common to most continental crusts. The current upper crust of the Chapleau block includes zones of reduced resistivity; the near-surface expression of the Ivanhoe Lake cataclastic zone (< 1 km in depth and 600 m in width), with resistivities of a few hundred ohm metres, is typical of fluid infilling weathered rocks. At least two other zones are less resistive (ρ < 12 kΩ∙m) than the typical upper-crustal Chapleau block (> 40 kΩ∙m), these include a subhorizontal layer at ~ 5 km and a subhorizontal to dipping layer at ~ 2 km. The deeper layer is interpreted as imaging deep fluids (porosities > 0.5%) postdating the uplift. The shallower feature, possibly related to the seismically detected detachment zone dipping at ~ 15° could be imaging conductors such as recent fluids or remnants of solid films precipitated at grain boundaries by more ancient fluids.Auger spectrometry of high-grade rocks exposed near the extrapolated surface expression of the shallower conductor reveals that fragments of graphite films (3–30 nm thick) are commonly found at grain boundaries, whereas traces of sulphur and chlorine are relatively rare. The electrical resistivity of these rocks was measured in laboratory and is lower than normally observed for similar high-grade rocks from other parts of the Canadian shield (5–25 kΩ∙m as opposed to 30–100 kΩ∙m).The Kapuskasing Uplift has opened a new area of research on upper-mantle conductivity structure from surface electromagnetic field measurements, an endeavour believed impossible until now.

scholarly journals Upper mantle conductivity structure of the back-arc region beneath northeastern China

2001 ◽  
Vol 28 (19) ◽  
pp. 3773-3776 ◽  
Author(s):  
Masahiro Ichiki ◽  
Makoto Uyeshima ◽  
Hisashi Utada ◽  
Zhao Guoze ◽  
Tang Ji ◽  
...  
Keyword(s):  
Upper Mantle ◽  
Northeastern China ◽  
Conductivity Structure ◽  
Mantle Conductivity ◽  
Back Arc

Magneto-telluric determination of upper mantle conductivity structure at Victoria, British Columbia

1968 ◽  
Vol 5 (5) ◽  
pp. 1209-1220 ◽  
Author(s):  
B. Caner ◽  
D. R. Auld
Keyword(s):  
Spectral Analysis ◽  
Upper Mantle ◽  
High Resistivity ◽  
Conducting Layer ◽  
Frequency Range ◽  
Tidal Effects ◽  
Conductivity Structure ◽  
Wide Range ◽  
Mantle Conductivity

Magneto-telluric data were obtained at Victoria over a very wide range of periods (2 s to 86 400 s). Only the data up to 15 000 s periods were used for interpretation of conductivity structure, since telluric data at longer periods were dominated by ocean-tidal effects; spectral analysis of one year's data was used to demonstrate the tidal effects. The telluric signals are strongly polarized in the whole frequency range, indicating an anisotropy in surface conductivity.The data indicate the existence of a finite conducting layer 10 ± 3 km thick and resistivity 100–125 ohm-meters, at a depth of 65 ± 5 km. A high resistivity zone (of the order of 4000–5000 ohm-meters) lies below this layer. There is no evidence for any further conducting zones down to a depth of at least 750 km.

scholarly journals Field Measurements of Surface and Near-Surface Turbulence in the Presence of Breaking Waves

2015 ◽  
Vol 45 (4) ◽  
pp. 943-965 ◽  
Author(s):  
Peter Sutherland ◽  
W. Kendall Melville
Keyword(s):  
Field Experiments ◽  
North Pacific Ocean ◽  
Large Fraction ◽  
Field Measurements ◽  
Breaking Waves ◽  
Sea Surface ◽  
Near Surface ◽  
Wave Energy Dissipation ◽  
Eddy Simulation ◽  
The North

AbstractWave breaking removes energy from the surface wave field and injects it into the upper ocean, where it is dissipated by viscosity. This paper presents an investigation of turbulent kinetic energy (TKE) dissipation beneath breaking waves. Wind, wave, and turbulence data were collected in the North Pacific Ocean aboard R/P FLIP, during the ONR-sponsored High Resolution Air-Sea Interaction (HiRes) and Radiance in a Dynamic Ocean (RaDyO) experiments. A new method for measuring TKE dissipation at the sea surface was combined with subsurface measurements to allow estimation of TKE dissipation over the entire wave-affected surface layer. Near the surface, dissipation decayed with depth as z−1, and below approximately one significant wave height, it decayed more quickly, approaching z−2. High levels of TKE dissipation very near the sea surface were consistent with the large fraction of wave energy dissipation attributed to non-air-entraining microbreakers. Comparison of measured profiles with large-eddy simulation results in the literature suggests that dissipation is concentrated closer to the surface than previously expected, largely because the simulations did not resolve microbreaking. Total integrated dissipation in the water column agreed well with dissipation by breaking for young waves, (where cm is the mean wave frequency and is the atmospheric friction velocity), implying that breaking was the dominant source of turbulence in those conditions. The results of these extensive measurements of near-surface dissipation over three field experiments are discussed in the context of observations and ocean boundary layer modeling efforts by other groups.

Mirror fault formation and coseismic slip at surface conditions: an example of faulting in unconsolidated deposits in the Central Apennines (Italy)

2021 ◽  
Author(s):  
Matteo Demurtas ◽  
Oliver Plümper ◽  
Markus Ohl ◽  
Fabrizio Balsamo ◽  
Mattia Pizzati
Keyword(s):  
Grain Boundaries ◽  
Amorphous Material ◽  
Hanging Wall ◽  
Microstructural Analysis ◽  
Central Apennines ◽  
Near Surface ◽  
Fault Surface ◽  
Mechanics Of Faulting ◽  
Seismic Rupture ◽  
Late Pleistocene To Holocene

&lt;p&gt;Faulting in seismically active regions commonly involves the deformation of unconsolidated to poorly lithified sediments at shallow to near-surface depths. When compared to classic crustal strength profiles that predict a velocity-strengthening behaviour for the first few km of depth, the propagation of seismic rupture to the surface appears counterintuitive. Rock deformation experiments have shown an inverse relationship between normal stress and displacement needed to the onset of dynamic weakening during seismic slip, meaning that for a seismic rupture to be able to propagate towards the surface, displacements should be large enough to counter the progressive decrease of normal and confining stresses.&lt;/p&gt;&lt;p&gt;In this contribution, we document the occurrence of mirror-like faults that formed within 20-30 m-thick, unconsolidated colluvium fan deposits at the hanging wall of the active Vado di Corno Fault Zone (VCFZ) in the Central Apennines, Italy. The deposits lie in direct contact with the master normal-fault surface, are Late Pleistocene to Holocene in age, and consist of angular carbonate clasts with grain size ranging ~0.1-10 mm derived from the dismantling of the adjacent VCFZ footwall. Field observations of cross cutting relationships and marker layer displacements suggest a maximum formation depth of the faults of c. 20-30 m and slip accommodated along single faults on the order of few cm. Faults are organised in three sets: subvertical, N-S and NE-SW trending faults, and WNW-ESE striking faults, synthetic and antithetic to the VCFZ master fault surface (N195/55&amp;#176;). Faults are commonly lineated with a dip-slip to slightly oblique kinematic.&lt;/p&gt;&lt;p&gt;Detailed microstructural analysis of the mirror faults shows extreme strain localization on a 2-5 &amp;#181;m thick principal slip zone composed of calcite nanograins ranging 10s-100s nm in size with amorphous material and phyllosilicates occurring along grain boundaries and within intragranular porosity. Locally, aggregates of nanograins coalesce and transition to &amp;#181;m-sized polygonal, larger grains. Calcite nanograins are mostly equant, with straight grain boundaries, 120&amp;#176; dihedral angles, and negligible porosity. These microstructures strongly resemble high temperature recrystallization structures documented along seismic faults exhumed from &gt;5 km of depth, where stresses are significantly larger. In our case, field constraints show that deformation occurred in very confining stress conditions and with limited displacement.&lt;/p&gt;&lt;p&gt;Collectively, our observations provide new documentation on the conditions for the formation of mirror faults and new insights into the mechanics of faulting and strain accommodation in the shallowest part of the crust (&lt; 1 km).&lt;/p&gt;

Inversion of the satellite observations of the tidally induced magnetic field in terms of 3-D upper-mantle electrical conductivity: Method and synthetic tests

2021 ◽  
Author(s):  
Libor Šachl ◽  
Jakub Velímský ◽  
Javier Fullea
Keyword(s):  
Magnetic Field ◽  
Electrical Conductivity ◽  
Upper Mantle ◽  
Spherical Harmonic ◽  
Model Space ◽  
Conductivity Method ◽  
Satellite Gravity ◽  
Compositional Model ◽  
Mantle Conductivity ◽  
The Impact

&lt;p&gt;&lt;span&gt;&lt;span&gt;We have developed and tested a new frequency-domain, spherical harmonic-finite element approach to the inverse problem of global electromagnetic (EM) induction. It is based on the quasi-Newton minimization of data misfit and regularization, and uses the adjoint approach for fast calculation of misfit gradients in the model space. Thus, it allows for an effective inversion of satellite-observed magnetic field induced by tidally driven flows in the Earth's oceans in terms of 3-D structure of the electrical conductivity in the upper mantle.&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt; Before proceeding to the inversion of Swarm-derived models of tidal magnetic signatures, we have performed a series of &lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;parametric studies&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;, using a 3-D conductivity model WINTERC-e as a testbed.&lt;/span&gt;&lt;/span&gt;&lt;/p&gt;&lt;p&gt;&lt;span&gt;The WINTERC-e model has been derived using state-of-the-art laboratory conductivity measurements of mantle minerals, and thermal and compositional model of the lithosphere and upper mantle WINTERC-grav. The latter model is based on the inversion of global surface waveforms, satellite gravity and gradiometry measurements, surface elevation, and heat flow data &lt;/span&gt;&lt;span&gt;&lt;span&gt;in a thermodynamically self-consistent framework. &lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;Therefore, the WINTERC-e model, independent of any EM data, represents an ideal target for synthetic tests of the 3-D EM inversion.&lt;/span&gt;&lt;/span&gt;&lt;span&gt; &lt;/span&gt;&lt;/p&gt;&lt;p&gt;&lt;span&gt;&lt;span&gt;We tested the impact of &lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;the &lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;satellite &lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;altitude&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;, &lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;the truncation degree of the &lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;spherical-harmonic &lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;expansion of the tidal signals, the random&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt; noise in data&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;,&lt;/span&gt;&lt;/span&gt;&lt;span&gt; &lt;/span&gt;&lt;span&gt;&lt;span&gt;and &lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;of the &lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;sub-&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;continental conductivity&lt;/span&gt;&lt;/span&gt;&lt;span&gt; &lt;/span&gt;&lt;span&gt;&lt;span&gt;on the &lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;ability to recover the sub-oceanic upper-mantle conductivity structure.&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt; We &lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;demonstrate &lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;that &lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;with &lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;suitable regularization &lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;we&lt;/span&gt;&lt;/span&gt;&lt;span&gt; &lt;/span&gt;&lt;span&gt;&lt;span&gt;can successfully reconstruct the 3D upper-mantle conductivity below world oceans.&lt;/span&gt;&lt;/span&gt;&lt;/p&gt;

Are There Better Disposal Methods?

2000 ◽  
Author(s):  
Hans Tammemagi
Keyword(s):  
Sustainable Development ◽  
Waste Disposal ◽  
Surface Expression ◽  
Abandoned Mines ◽  
Underground Mines ◽  
Open Pit ◽  
Near Surface ◽  
The Sustainable Development ◽  
Future Value ◽  
Deep Underground

Most of the solid waste generated by society ultimately winds up in near-surface landfills. Let us put our thinking caps firmly on, place our prejudices aside, and explore what other methods might be used to dispose of waste. We should seek, in particular, the approaches that best fulfill the three basic principles described in chapter 2. That is, we should strive to find disposal methods that are in accord with sustainable development. Existing and abandoned pits, quarries, and mines are attractive for waste disposal because a hole to contain the wastes has already been excavated. Such abandoned areas, when left unreclaimed, cannot be used for agriculture or other beneficial uses. Thus, they generally do not have significant market value and can often be obtained relatively cheaply. For these reasons, pits and quarries have been extensively used for landfills. Operating and abandoned mines, on which this section focuses, are somewhat similar to pits and quarries, though usually larger. Abandoned mines hold promise as disposal facilities because they are resource areas that have been depleted and thus have little future value. There are two basic types of mine: the open pit mine, which is effectively a large pit or hole in the ground; and the underground mine, where the mined-out openings are deep underground and there is no surface expression except for the shafts used to gain subsurface access. Because underground mines occupy minimal surface land, their use for waste disposal would be in accordance with the sustainable development principles that were advocated in chapter 2. Several European countries, with higher population densities and much smaller land mass than in North America, have long used abandoned underground mines to dispose of their rubbish. The major advantage of placing wastes deep in underground mines is that it is inherently safer than placing the wastes in a surface facility. The amount of groundwater and its flow rate decrease with depth; this fact, combined with the long transport paths back to the biosphere, minimizes the possibility that contaminants will be carried by groundwater to the surface, where they could damage the environment. The waste is contained deeper and more securely.

scholarly journals Seismic anisotropy reveals crustal flow driven by mantle vertical loading in the Pacific NW

2020 ◽  
Vol 6 (28) ◽  
pp. eabb0476
Author(s):  
Jorge C. Castellanos ◽  
Jonathan Perry-Houts ◽  
Robert W. Clayton ◽  
YoungHee Kim ◽  
A. Christian Stanciu ◽  
...  
Keyword(s):  
Pacific Northwest ◽  
Upper Mantle ◽  
Seismic Anisotropy ◽  
Azimuthal Anisotropy ◽  
Mantle Flow ◽  
Near Surface ◽  
Vertical Loading ◽  
The Pacific ◽  
Anisotropy Model ◽  
Lithosphere Dynamics

Buoyancy anomalies within Earth’s mantle create large convective currents that are thought to control the evolution of the lithosphere. While tectonic plate motions provide evidence for this relation, the mechanism by which mantle processes influence near-surface tectonics remains elusive. Here, we present an azimuthal anisotropy model for the Pacific Northwest crust that strongly correlates with high-velocity structures in the underlying mantle but shows no association with the regional mantle flow field. We suggest that the crustal anisotropy is decoupled from horizontal basal tractions and, instead, created by upper mantle vertical loading, which generates pressure gradients that drive channelized flow in the mid-lower crust. We then demonstrate the interplay between mantle heterogeneities and lithosphere dynamics by predicting the viscous crustal flow that is driven by local buoyancy sources within the upper mantle. Our findings reveal how mantle vertical load distribution can actively control crustal deformation on a scale of several hundred kilometers.

scholarly journals The Role of Horizontal Divergence in Submesoscale Frontogenesis

2019 ◽  
Vol 49 (6) ◽  
pp. 1593-1618 ◽  
Author(s):  
Roy Barkan ◽  
M. Jeroen Molemaker ◽  
Kaushik Srinivasan ◽  
James C. McWilliams ◽  
Eric A. D’Asaro
Keyword(s):  
Numerical Simulations ◽  
Analytical Solutions ◽  
Field Measurements ◽  
Careful Analysis ◽  
Rossby Number ◽  
Asymptotic Model ◽  
Near Surface ◽  
Boundary Layer Turbulence ◽  
Oceanic Surface ◽  
Gradient Fields

AbstractOceanic surface submesoscale currents are characterized by anisotropic fronts and filaments with widths from 100 m to a few kilometers; an O(1) Rossby number; and large magnitudes of lateral buoyancy and velocity gradients, cyclonic vorticity, and convergence. We derive an asymptotic model of submeoscale frontogenesis—the rate of sharpening of submesoscale gradients—and show that in contrast with “classical” deformation frontogenesis, the near-surface convergent motions, which are associated with the ageostrophic secondary circulation, determine the gradient sharpening rates. Analytical solutions for the inviscid Lagrangian evolution of the gradient fields in the proposed asymptotic regime are provided, and emphasize the importance of ageostrophic motions in governing frontal evolution. These analytical solutions are further used to derive a scaling relation for the vertical buoyancy fluxes that accompany the gradient sharpening process. Realistic numerical simulations and drifter observations in the northern Gulf of Mexico during winter confirm the applicability of the asymptotic model to strong frontogenesis. Careful analysis of the numerical simulations and field measurements demonstrates that a subtle balance between boundary layer turbulence, pressure, and Coriolis effects (e.g., turbulent thermal wind; Gula et al. 2014) leads to the generation of the surface convergent motions that drive frontogenesis in this region. Because the asymptotic model makes no assumptions about the physical mechanisms that initiate the convergent frontogenetic motions, it is generic for submesoscale frontogenesis of O(1) Rossby number flows.

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