Thermoelectrical self‐potential anomalies and their relationship to the solid angle subtended by the source region

Geophysics ◽  
1984 ◽  
Vol 49 (2) ◽  
pp. 165-170 ◽  
Author(s):  
David V. Fitterman
Keyword(s):  
Weighting Function ◽  
Solid Angle ◽  
Source Region ◽  
Geothermal Field ◽  
Observation Point ◽  
Constant Intensity ◽  
Self Potential ◽  
Sp Anomaly

The calculation of self‐potential (SP) anomalies produced by thermoelectric sources is shown to be equivalent to calculating the weighted solid angle subtended at the observation point by the source region and its images where the weighting function is the source intensity. This interpretation provides an easy way of visualizing the effect of different source geometries, and describes the nonuniqueness associated with SP sources. For example, changes in a model which keep the product of source intensity and area constant do not appreciably change the produced anomaly. Similarly, deepening a source requires an increase of source intensity or size to produce the same anomaly. When conductivity contrasts become small or nonexistent, the number of image sources becomes finite or zero, respectively, further simplifying the calculation. As an example, the SP anomaly of a dipping rectangular source of constant intensity is computed using the method. This model is applied to SP data from the East Mesa geothermal field.

Modeling of self‐potential anomalies near vertical dikes

Geophysics ◽  
1983 ◽  
Vol 48 (2) ◽  
pp. 171-180 ◽  
Author(s):  
David V. Fitterman
Keyword(s):  
Field Data ◽  
Source Region ◽  
The Self ◽  
Model Parameters ◽  
Dc Resistivity ◽  
Constant Intensity ◽  
Source Regions ◽  
Source Mechanisms ◽  
Self Potential ◽  
Sp Anomaly

The self‐potential (SP) Green’s function for an outcropping vertical dike is derived from solutions for the dc resistivity problem for the same geometry. The Green’s functions are numerically integrated over rectangular source regions on the contacts between the dike and the surrounding material to obtain the SP anomaly. The analysis is valid for thermoelectrical source mechanisms. Two types of anomalies can be produced by this geometry. When the two source planes are polarized in opposite directions, a monopolar anomaly is produced. This corresponds to the thermoelectrical properties of the dike being in contrast with the surrounding material. When the thermoelectric coefficients change monotonically across the dike, a dipolar anomaly is produced. In either case positive and negative anomalies are possible, and the greatest variation in potential will occur in the most resistive regions. Examples of the effect of changing different model parameters are given for sources that have constant intensity throughout the rectangular source regions. For these patch models the depth to the top of the source region is approximately equal to the distance between the minimum (or maximum) of the anomaly outside of the dike and the edge of the dike. Field data collected over a hot intrusive fissure are presented which have been modeled by the technique described.

Inversion of self‐potential data from the Cerro Prieto geothermal field, Mexico

Geophysics ◽  
1982 ◽  
Vol 47 (6) ◽  
pp. 938-945 ◽  
Author(s):  
David V. Fitterman ◽  
Robert F. Corwin
Keyword(s):  
Source Region ◽  
Geothermal Field ◽  
Reservoir Rock ◽  
Coupling Coefficients ◽  
Vertical Extent ◽  
Potential Source ◽  
Cerro Prieto ◽  
Vertical Contact ◽  
Self Potential ◽  
Production Zone

Self‐potential (SP) data from the Cerro Prieto geothermal field in Baja California, Mexico have been inverted using a model consisting of a vertical contact separating regions of different electrical properties. A temperature source is assumed to coincide with the vertical contact between materials with different thermoelectric coupling coefficients. A derivative‐free Levenberg‐Marquardt algorithm is used to estimate values for the depth, vertical extent, length, and intensity of the source region. The depth to the top of the source is estimated to be about 1.3 ± 0.2 km, which agrees quite well with the depth to the top of the production zone determined from drilling. The vertical extent and length of the source region are estimated to be 11 ± 3 km and 9.9 ± 0.4 km, respectively. There appears to be geologic evidence for the presence of a fault or fault zone within the geothermal field that roughly coincides in location with the self‐potential source region. The conductivity on the east side of the production zone is estimated to be 80 percent of the value to the west, which is in general agreement with field resistivity measurements. Thermoelectric coupling coefficients measured in the laboratory on samples of reservoir rock are not large enough to explain the −340 ± 40 mV source intensity predicted by the model, possibly because the laboratory measurements were made at temperatures about 300°C lower than the reservoir value. These results do not rule out the possibility of a streaming potential source mechanism.

Calculations of self‐potential anomalies near vertical contacts

Geophysics ◽  
1979 ◽  
Vol 44 (2) ◽  
pp. 195-205 ◽  
Author(s):  
David V. Fitterman
Keyword(s):  
Physical Mechanism ◽  
Chemical Potential ◽  
Source Region ◽  
Streaming Potential ◽  
Source Mechanism ◽  
Constant Intensity ◽  
Potential Gradients ◽  
Vertical Contact ◽  
Chemical Potential Gradients ◽  
Self Potential

The self‐potential anomalies due to streaming potential effects in the vicinity of a vertical contact are analyzed. This approach is different from most previous studies in that the source is tied to a specific physical mechanism instead of arbitrarily selected charge distributions or current sources. The analysis is valid for any source mechanism that can be thought of in terms of crosscoupled flows, e.g., the thermoelectric effect or chemical potential gradients. The anomalies tend to be antisymmetric across the contact with the magnitude of the anomaly being larger on the more resistive side of the contact. An analytic expression for the case of a constant intensity, rectangular source is derived from the general solution. The anomalies for this simple case are computable with a handheld calculator and can be used to estimate the location, extent, and magnitude of the anomaly source region. With this information it is possible to determine the most probable crosscoupling source mechanism.

scholarly journals Implications of Self-Potential Distribution for Groundwater Flow System in a Nonvolcanic Mountain Slope

2012 ◽  
Vol 2012 ◽  
pp. 1-10 ◽  
Author(s):  
Tada-nori Goto ◽  
Kazuya Kondo ◽  
Rina Ito ◽  
Keisuke Esaki ◽  
Yasuo Oouchi ◽  
...  
Keyword(s):  
Groundwater Flow ◽  
General Trend ◽  
Flow System ◽  
Ground Surface ◽  
Mountain Slope ◽  
Infiltration Process ◽  
Groundwater Flow System ◽  
Self Potential ◽  
Sp Anomaly ◽  
Fft Analysis

Self-potential (SP) measurements were conducted at Mt. Tsukuba, Japan, which is a nonvolcanic mountain, to infer groundwater flow system in the mountain. Survey routes were set around the northern slope, and the reliability of observed SP anomaly was checked by using SP values along parallel survey routes; the error was almost within 10 mV. The FFT analysis of the spatial SP distribution allows us a separation of raw data into two components with shorter and longer wavelength. In the shorter (altitudinal) wavelength than ∼200 meters, several positive SP peaks of more than 100 mV in magnitude are present, which indicate shallow perched water discharges along the slope. In the regional SP pattern of longer wavelength, there are two major perturbations from the general trend reflecting the topographic effect. By comparing the SP and hydrological data, the perturbation around the foothill is interpreted to be caused by heterogeneous infiltration at the ground surface. The perturbation around the summit is also interpreted to be caused by heterogeneous infiltration process, based on a simplified numerical modeling of SP. As a result, the SP pattern is well explained by groundwater flow and infiltration processes. Thus, SP data is thought to be very useful for understanding of groundwater flow system on a mountain scale.

scholarly journals Monte-Carlo simulations of external dose contributions from the surrounding ground areas of residential homes in a typical Northern European suburban area after a radioactive fallout scenario

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Yvonne Hinrichsen ◽  
Robert Finck ◽  
Johan Martinsson ◽  
Christopher Rääf
Keyword(s):  
Monte Carlo ◽  
Radiation Dose ◽  
Negative Impact ◽  
Theoretical Calculations ◽  
Source Region ◽  
Monte Carlo Model ◽  
Observation Point ◽  
Suburban Area ◽  
Radiation Doses ◽  
Property A

Abstract The emissions of $$^{137}\hbox {Cs}$$ 137 Cs into the environment from the nuclear accidents in Chernobyl in 1986 and Fukushima in 2011 led to the need to decontaminate large areas to avert radiation doses to the population in the affected areas. To be able to perform cost-effective and sustainable remediation, knowledge is needed about how radiation doses can be minimized through optimized interventions such that the greatest possible reduction in radiation dose is obtained with the smallest possible negative impact on the area. Theoretical calculations have been performed to determine how radiation doses in single family houses in a typical Swedish residential suburb arise from a hypothetical $$^{137}\hbox {Cs}$$ 137 Cs deposition on the ground. The intention was to highlight how remediation of different parts of the surroundings affects the radiation dose to the residents in a particular property. A Monte Carlo model of the houses and the environment in a suburban area was set up to allow calculations of the dose contributions from different contaminated ground areas such as their own property, neighbouring properties, streets and surrounding recreational areas. Calculations were performed for eleven observation points inside different rooms of the house and one observation point in the garden outside the house, for four houses in the neighbourhood, and for two types of building construction material. The influence of the time spent in different rooms of the house and the contamination of areas surrounding the house was studied. The results show that in general the main dose contribution originates from their own property, but that a significant part (30–80%, depending on the observation point) can come from other areas, showing the importance of considering the surroundings in remediation actions. More detailed analysis of the results showed that the dose contribution from a source region is in general highly dependent on the position of windows in a brick house, whereas for a wooden house the distance to the source region is also of relevance.

RESISTIVITY, SELF‐POTENTIAL, AND INDUCED‐POLARIZATION SURVEYS OF A VAPOR‐DOMINATED GEOTHERMAL SYSTEM

Geophysics ◽  
1973 ◽  
Vol 38 (6) ◽  
pp. 1130-1144 ◽  
Author(s):  
A. A. R. Zohdy ◽  
L. A. Anderson ◽  
L. J. P. Muffler
Keyword(s):  
Geothermal Field ◽  
Induced Polarization ◽  
Hot Water ◽  
Thermal Waters ◽  
Geothermal System ◽  
Electrical Soundings ◽  
Lateral Extent ◽  
High Concentrations ◽  
Lake Deposits ◽  
Self Potential

The Mud Volcano area in Yellowstone National Park provides an example of a vapor‐dominated geothermal system. A test well drilled to a depth of about 347 ft penetrated the vapor‐dominated reservoir at a depth of less than 300 ft. Subsequently, 16 vertical electrical soundings (VES) of the Schlumberger type were made along a 3.7‐mile traverse to evaluate the electrical resistivity distribution within this geothermal field. Interpretation of the VES curves by computer modeling indicates that the vapor‐dominated layer has a resistivity of about 75–130 ohm‐m and that its lateral extent is about 1 mile. It is characteristically overlain by a low‐resistivity layer of about 2–6.5 ohm‐m, and it is laterally confined by a layer of about 30 ohm‐m. This 30‐ohm‐m layer, which probably represents hot water circulating in low‐porosity rocks, also underlies most of the survey at an average depth of about 1000 ft. Horizontal resistivity profiles, measured with two electrode spacings of an AMN array, qualitatively corroborate the sounding interpretation. The profiling data delineate the southeast boundary of the geothermal field as a distinct transition from low to high apparent resistivities. The northwest boundary is less distinctly defined because of the presence of thick lake deposits of low resistivities. A broad positive self‐potential anomaly is observed over the geothermal field, and it is interpretable in terms of the circulation of the thermal waters. Induced‐polarization anomalies were obtained at the northwest boundary and near the southeast boundary of the vapor‐dominated field. These anomalies probably are caused by relatively high concentrations of pyrite.

On the Polarization and Rapid Fade-out of Moving Type IV Solar Bursts

1970 ◽  
Vol 1 (8) ◽  
pp. 372-374 ◽  
Author(s):  
G. A. Dulk
Keyword(s):  
Synchrotron Radiation ◽  
Circular Polarization ◽  
Source Region ◽  
Relativistic Electrons ◽  
Constant Intensity ◽  
Precise Position ◽  
Polarization Measurements ◽  
Type Iv ◽  
Solar Bursts

Since the advent of the 80 MHz radioheliograph, precise position and polarization measurements have become available on several moving type IV bursts. Two of the more puzzling characteristics of these bursts are : (1) they exhibit strong circular polarization in parts or all of the source region ; (2) after moving outward to as much as 3 R⊙ with relatively constant intensity, they rapidly fade away. In this paper we discuss the polarization and intensity of synchrotron radiation from mildly relativistic electrons and suggest betatron deceleration as a mechanism to explain the rapid fade-out of the moving type IV sources. The results are applied to two examples of moving type IV bursts.

An analytical method to interpret self‐potential anomalies caused by 2-D inclined sheets

Geophysics ◽  
1998 ◽  
Vol 63 (5) ◽  
pp. 1551-1555 ◽  
Author(s):  
N. Sundararajan ◽  
P. Srinivasa Rao ◽  
V. Sunitha
Keyword(s):  
Surrounding Medium ◽  
Mathematical Expression ◽  
Constant Term ◽  
Hilbert Transforms ◽  
The Hilbert Transform ◽  
Point Of Intersection ◽  
Self Potential ◽  
Derivatives Of ◽  
Sp Anomaly ◽  
Inclined Sheet

The first‐order horizontal and vertical derivatives of the self‐potential (SP) anomalies caused by a 2-D inclined sheet of infinite horizontal extent are analysed to obtain the depth h, the half width a, the inclination α and the constant term containing the resistivity ρ and the current density I of the surrounding medium. The vertical derivative of the SP anomaly is obtained from the horizontal derivative via the Hilbert transform, which is also redefined to yield a modified version, a 270° phase shift of the original function. The point of intersection of these two Hilbert transforms corresponds to the origin. The amplitudes constitute a similar case. The practicability of the method is tested on a theoretical example as well as on field data from the Surda area of Rakha mines, Singhbhum belt, Bihar, India. The results agree well with those of other methods in use. Since the procedure is based on a simple mathematical expression involving the real roots of the derivatives, it can easily be automated.

Sign in / Sign up

Export Citation Format

Share Document