A THEORETICAL STUDY OF INDUCED ELECTRICAL POLARIZATION

Geophysics ◽  
1957 ◽  
Vol 22 (3) ◽  
pp. 688-706 ◽  
Author(s):  
Richard H. Frische ◽  
Haro von Buttlar
Keyword(s):  
Ground Water ◽  
Theoretical Study ◽  
Polarization Potential ◽  
Potential Difference ◽  
Electrode Configuration ◽  
Laboratory Model ◽  
Earth Model ◽  
Mathematical Solution ◽  
Electrical Polarization ◽  
Earth Models

A mathematical solution is obtained and numerically evaluated for determining the depth to a saturated aquifer when prospecting for ground water by induced electrical polarization. In a horizontally stratified earth model consisting of a nonpolarizable overburden and an underlying, infinitely deep polarizable layer, the induced‐polarization potential difference for a Wenner electrode configuration is nearly independent of the resistivity contrast. The computation agrees with results from a laboratory model tank and with a field curve. This justifies confidence in the validity of the results obtained from the model tank on earth models too complex for computation.

scholarly journals Viscous Effects in the Solid Earth Response to Modern Antarctic Ice Mass Flux: Implications for Geodetic Studies of WAIS Stability in a Warming World

2020 ◽  
Vol 33 (2) ◽  
pp. 443-459 ◽  
Author(s):  
E. Powell ◽  
N. Gomez ◽  
C. Hay ◽  
K. Latychev ◽  
J. X. Mitrovica
Keyword(s):  
Mass Flux ◽  
Crustal Deformation ◽  
Earth Model ◽  
Elastic Model ◽  
West Antarctica ◽  
Viscous Effects ◽  
Quarter Century ◽  
Viscosity Models ◽  
Earth Models ◽  
Warming World

AbstractThe West Antarctic Ice Sheet (WAIS) overlies a thin, variable-thickness lithosphere and a shallow upper-mantle region of laterally varying and, in some regions, very low (~1018 Pa s) viscosity. We explore the extent to which viscous effects may affect predictions of present-day geoid and crustal deformation rates resulting from Antarctic ice mass flux over the last quarter century and project these calculations into the next half century, using viscoelastic Earth models of varying complexity. Peak deformation rates at the end of a 25-yr simulation predicted with an elastic model underestimate analogous predictions that are based on a 3D viscoelastic Earth model (with minimum viscosity below West Antarctica of 1018 Pa s) by ~15 and ~3 mm yr−1 in the vertical and horizontal directions, respectively, at sites overlying low-viscosity mantle and close to high rates of ice mass flux. The discrepancy in uplift rate can be reduced by adopting 1D Earth models tuned to the regional average viscosity profile beneath West Antarctica. In the case of horizontal crustal rates, adopting 1D regional viscosity models is no more accurate in recovering predictions that are based on 3D viscosity models than calculations that assume a purely elastic Earth. The magnitude and relative contribution of viscous relaxation to crustal deformation rates will likely increase significantly in the next several decades, and the adoption of 3D viscoelastic Earth models in analyses of geodetic datasets [e.g., Global Navigation Satellite System (GNSS); Gravity Recovery and Climate Experiment (GRACE)] will be required to accurately estimate the magnitude of Antarctic modern ice mass flux in the progressively warming world.

Validity of Resolving the 785 km Discontinuity in the Lower Mantle with P′P′ Precursors?

2020 ◽  
Vol 91 (6) ◽  
pp. 3278-3285
Author(s):  
Baolong Zhang ◽  
Xiangfang Zeng ◽  
Jun Xie ◽  
Vernon F. Cormier
Keyword(s):  
Lower Mantle ◽  
Forward Modeling ◽  
Earth Model ◽  
Frequency Content ◽  
Waveform Data ◽  
Mantle Discontinuities ◽  
The Earth ◽  
Earth Models ◽  
Beamforming Technique ◽  
Ray Paths

Abstract P ′ P ′ precursors have been used to detect discontinuities in the lower mantle of the Earth, but some seismic phases propagating along asymmetric ray paths or scattered waves could be misinterpreted as reflections from mantle discontinuities. By forward modeling in standard 1D Earth models, we demonstrate that the frequency content, slowness, and decay with distance of precursors about 180 s before P′P′ arrival are consistent with those of the PKPPdiff phase (or PdiffPKP) at epicentral distances around 78° rather than a reflection from a lower mantle interface. Furthermore, a beamforming technique applied to waveform data recorded at the USArray demonstrates that PKPPdiff can be commonly observed from numerous earthquakes. Hence, a reference 1D Earth model without lower mantle discontinuities can explain many of the observed P′P′ precursors signals if they are interpreted as PKPPdiff, instead of P′785P′. However, this study does not exclude the possibility of 785 km interface beneath the Africa. If this interface indeed exists, P′P′ precursors at distances around 78° would better not be used for its detection to avoid interference from PKPPdiff. Indeed, it could be detected with P′P′ precursors at epicentral distances less than 76° or with other seismic phases such as backscattered PKP·PKP waves.

Improving teleseismic event locations using a three-dimensional Earth model

1996 ◽  
Vol 86 (3) ◽  
pp. 788-796 ◽  
Author(s):  
Gideon P. Smith ◽  
Göran Ekström
Keyword(s):  
Large Scale ◽  
Three Dimensional ◽  
The United States ◽  
Earth Model ◽  
Published Data ◽  
S Wave ◽  
Origin Time ◽  
Data Set ◽  
Station Corrections ◽  
Earth Models

Abstract A comparison is made between seismic event locations derived from standard spherically symmetric Earth models (JB, PREM, IASP91) and a recent Earth model (S&P12/WM13) that incorporates large-scale lateral heterogeneity of P- and S-wave velocities in the mantle. Events with known hypocentral coordinates are located in the different Earth models using standard methods. Two sets of events are considered: a data set of 26 explosions, including primarily nuclear weapons test explosions and peaceful nuclear explosions in the United States and former USSR; and a published data set of 82 well-located earthquakes with a more even global distribution. IASP91 and PREM are shown to offer similar errors in event location and origin time estimates with respect to the JB model. The three-dimensional (3D) model S&P12/WM13 offers improvement in event locations over all three one-dimensional (1D) models with, or without, station corrections. For the explosion events, the average mislocation distance is reduced by approximately 40%; for the earthquakes, the improvements are smaller. Corrections for crustal thickness beneath source and receiver are found to be of similar magnitude to the mantle corrections, but use of station corrections together with the three-dimensional mantle model provide the best locations.

Overlapping Interests: The Impact of Geographic Coordinate Assumptions on Limited-Area Atmospheric Model Simulations

2013 ◽  
Vol 141 (6) ◽  
pp. 2120-2127 ◽  
Author(s):  
Andrew J. Monaghan ◽  
Michael Barlage ◽  
Jennifer Boehnert ◽  
Cody L. Phillips ◽  
Olga V. Wilhelmi
Keyword(s):  
Land Use ◽  
High Resolution ◽  
Input Data ◽  
Atmospheric Model ◽  
Earth Model ◽  
Limited Area ◽  
Near Surface ◽  
Geographic Coordinate System ◽  
Earth Models ◽  
The Impact

Abstract There is growing use of limited-area models (LAMs) for high-resolution (<10 km) applications, for which consistent mapping of input terrestrial and meteorological datasets is critical for accurate simulations. The geographic coordinate systems of most input datasets are based on spheroid-shaped (i.e., elliptical) Earth models, while LAMs generally assume a perfectly sphere-shaped Earth. This distinction is often neglected during preprocessing, when input data are remapped to LAM domains, leading to geolocation discrepancies that can exceed 20 km at midlatitudes. A variety of terrestrial (topography and land use) input dataset configurations is employed to explore the impact of Earth model assumptions on a series of 1-km LAM simulations over Colorado. For the same terrestrial datasets, the ~20-km geolocation discrepancy between spheroidal-versus-spherical Earth models over the domain leads to simulated differences in near-surface and midtropospheric air temperature, humidity, and wind speed that are larger and more widespread than those due to using different topography and land use datasets altogether but not changing the Earth model. Simulated differences are caused by the shift of static fields with respect to boundary conditions, and altered Coriolis forcing and topographic gradients. The sensitivity of high-resolution LAM simulations to Earth model assumptions emphasizes the importance for users to ensure terrestrial and meteorological input data are consistently mapped during preprocessing (i.e., datasets share a common geographic coordinate system before remapping to the LAM domain). Concurrently, the modeling community should update preprocessing systems to make sure input data are correctly mapped for all global and limited-area simulation domains.

scholarly journals Aplikasi Konfigurasi Wenner dalam Menganalisis Jenis Material Bawah Permukaan

2016 ◽  
Vol 5 (1) ◽  
pp. 95
Author(s):  
Hakim Hakim ◽  
Rahma Hi. Manrulu
Keyword(s):  
Ground Water ◽  
Electric Current ◽  
Electromagnetic Fields ◽  
Path Length ◽  
The Other ◽  
Potential Difference ◽  
Electrode Spacing ◽  
Local Conditions ◽  
The Earth ◽  
Working Principle

We analyzed the subsurface with Wenner configuration application. This study aims to determine the structure of the subsurface with Wenner configuration application. Wenner configuration is one of the geo-electric method, where this method is used to determine the nature of the flow of electricity in the earth in a way to detect it in the earth's surface. This detection covers potential measurements, currents and electromagnetic fields that occur either by injection or flow naturally. The working principle of geo-electric method is done by injecting an electric current into the ground through a pair of electrodes and measuring the potential difference with the other pair of electrodes. When an electric current is injected into a medium and measured the potential difference (voltage), then the value of the resistance of the medium can be estimated. Method of this research is to create a path for three (3) parallel to the trajectory made to local conditions study, the path length of 100 m and the electrode spacing of 5-7 m. The interpretation of the data obtained their ground water, rock conglomerate, limestone and granite at a depth of 17.4 m. Telah dilakukan analisis bawah permukaan dengan aplikasi konfigurasi Wenner. Penelitian ini bertujuan untuk mengetahui struktur lapisan bawah permukaan dengan aplikasi konfigurasi Wenner. Konfigurasi Wenner merupakan salah satu metode geolistrik, dimana metode ini merupakan metode yang digunakan untuk  mengetahui  sifat  aliran  listrik  di  dalam  bumi dengan  cara  mendeteksinya  di  permukaan  bumi. Pendeteksian ini meliputi pengukuran potensial, arus dan medan elektromagnetik  yang terjadi baik itu oleh injeksi arus maupun secara alamiah. Prinsip  kerja  metode geolistrik dilakukan dengan cara menginjeksikan arus listrik ke permukaan tanah melalui sepasang elektroda dan mengukur beda potensial dengan sepasang elektroda yang lain. Bila arus listrik  diinjeksikan ke dalam suatu medium dan diukur beda potensialnya (tegangan), maka nilai hambatan dari medium tersebut dapat diperkirakan. Metode kerja peneltian ini adalah membuat lintasan sebanyak 3 (tiga) lintasan yang dibuat sejajar dengan memperhatikan kondisi daerah penelitian, dengan panjang lintasan 100 m dan jarak elektroda 5-7 m. Hasil interpretasi data diperoleh adanya air tanah, batuan konglomerat, batu gamping dan batu granit pada kedalaman 17,4 m.

scholarly journals GANSim-3D for conditional geomodelling: theory and field application

2021 ◽  
Author(s):  
Suihong Song ◽  
Tapan Mukerji ◽  
Jiagen Hou ◽  
Dongxiao Zhang ◽  
Xinrui Lyu
Keyword(s):  
Carbon Capture And Storage ◽  
Training Dataset ◽  
Generative Adversarial Networks ◽  
Earth Model ◽  
Global Features ◽  
Probability Map ◽  
Probability Maps ◽  
Earth Models ◽  
Conditioning Data ◽  
Facies Models

Geomodelling of subsurface reservoirs is important for water resources, hydrocarbon exploitation, and Carbon Capture and Storage (CCS). Traditional geostatistics-based approaches cannot abstract complex geological patterns and are thus not able to simulate very realistic earth models. We present a Generative Adversarial Networks (GANs)-based 3D reservoir simulation framework, GANSim-3D, which can capture geological patterns and relationships between various conditioning data and earth models and is thus able to directly simulate multiple 3D realistic and conditional earth models of arbitrary sizes from given conditioning data. In GANSim-3D, the generator, designed to only include 3D convolutional layers, takes various 3D conditioning data and 3D random latent cubes (composed of random numbers) as inputs and produces a 3D earth model. Two types of losses, the original GANs loss and condition-based loss, are designed to train the generator progressively from shallow to deep layers to learn the geological patterns and relationships from coarse to fine resolutions. Conditioning data can include 3D sparse well facies data, 3D low-resolution probability maps, and global features like facies proportion, channel width, etc. Once trained on a training dataset where each training sample is a 3D cube of a small fixed size, the generator can be used for geomodelling of 3D reservoirs of large arbitrary sizes by directly extending the sizes of all inputs and the output of the generator proportionally. To illustrate how GANSim-3D is used for field geomodelling and also to verify GANSim-3D, a field karst cave reservoir in Tahe area of China is used as an example. The 3D well facies data and 3D probability map of caves obtained from geophysical interpretation are used as conditioning data. First, we create a training dataset consisting of facies models of 64×64×64 cells with a process-mimicking simulation method to integrate field geological patterns. The training well facies data and the training probability map data are produced from the training facies models. Then, the 3D generator is successfully trained and evaluated in two synthetic cases with various metrics. Next, we apply the pretrained generator for conditional geomodelling of two field cave reservoirs of Tahe area. The first reservoir is 800m×800m×64m and is divided into 64×64×64 cells, while the second is 4200m×3200m×96m and is divided into 336×256×96 cells. We fix the input well facies data and cave probability maps and randomly change the input latent cubes to allow the generator to produce multiple diverse cave reservoir realizations, which prove to be consistent with the geological patterns of real Tahe cave reservoir as well as the input conditioning data. The noise in the input probability map is suppressed by the generator. Once trained, the geomodelling process is quite fast: each realization with 336×256×96 cells takes 0.988 seconds using 1 GPU (V100). This study shows that GANSim-3D is robust for fast 3D conditional geomodelling of field reservoirs of arbitrary sizes.

Universal dispersion tables

1968 ◽  
Vol 58 (5) ◽  
pp. 1407-1499
Author(s):  
Don L. Anderson ◽  
David G. Harkrider
Keyword(s):  
Phase Velocity ◽  
Group Velocity ◽  
Love Waves ◽  
Arbitrary Distribution ◽  
Earth Model ◽  
Dispersion Theory ◽  
Dispersion Parameters ◽  
Partial Derivatives ◽  
Earth Models

Abstract The universal dispersion theory, presented in Part I, is extended to allow computation of group velocity and amplitude partial derivatives. Tables giving the effect of a change in any parameter on phase velocity, group velocity and amplitude are given for two earth models, one oceanic and one continental shield. Tables are given for the fundamental and first three higher Love modes. These tables make it possible to compute dispersion parameters for the first four Love modes for any realistic earth model or to invert observations to an earth model. Attenuation of Love waves for an arbitrary distribution of Q versus depth can also be computed by using techniques previously described.

scholarly journals Fast computation of a viscoelastic deformable Earth model for ice-sheet simulations

2007 ◽  
Vol 46 ◽  
pp. 97-105 ◽  
Author(s):  
Ed Bueler ◽  
Craig S. Lingle ◽  
Jed Brown
Keyword(s):  
Half Space ◽  
Elastic Plate ◽  
Integral Formula ◽  
Mathematical Formulation ◽  
Ice Sheet ◽  
Earth Model ◽  
Ice Flow ◽  
Earth Models ◽  
New Formulation ◽  
Made In

AbstractThe model used by Lingle and Clark (1985) to approximate the deformation of the Earth under a single ice stream is adapted to the purposes of continent-scale ice-sheet simulation. The model combines a layered elastic spherical Earth (Farrell, 1972) with a viscous half-space overlain by an elastic plate lithosphere (Cathles, 1975). For the half-space model we identify a new mathematical formulation, essentially a time-dependent partial differential equation, which generalizes and improves upon the standard elastic plate lithosphere with relaxing asthenosphere model widely used in ice-sheet simulation. The new formulation allows a significantly faster numerical strategy, a spectral collocation method based directly on the fast Fourier transform. We verify this method by comparing to an integral formula for a disk load. We also demonstrate that the magnitudes of numerical errors made in approximating coupled ice-flow/Earth-deformation systems are significantly smaller than pairwise differences between several Earth models. Our implementation of the Lingle and Clark (1985) model offers important features of spherical, layered, self-gravitating, viscoelastic Earth models without the computational expense.

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