Electrical Methods Flashcards
measure effects of electrical current flow in the Earth.
They include measurements of current flow, electrical potential, and electromagnetic fields.
Electrical Methods
Active method measuring electrical potential from subsurface current flow.
Detects pore fluids, clay presence, and quality.
DC Resistivity
Often used with DC Resistivity.
Measures transient variations in potential during current application or removal.
Detects clay concentrations and conductive minerals.
Induced Polarization (IP):
Passive method measuring naturally occurring electrical potentials.
Associated with sulfide ore weathering and groundwater flow.
Self Potential (SP)
Active method measuring time-varying magnetic fields from current flow.
Used in detecting conductive deposits, buried objects, and near-surface mapping.
Electromagnetic EM
Passive method using naturally occurring electrical currents from magnetic induction.
Determines electrical properties at great depths inside the Earth.
Magnetotelluric (MT)
Defines the relationship between current, voltage, and resistance.
Resistivity measures a material’s ability to transmit electric current, independent of geometry.
Ohm’s Law and Resistivity
Lists resistivity values for various Earth materials.
Controlled primarily by pore fluids and fractures filled with fluids.
Resistivities of Earth Materials
Requires current source, ammeter, voltmeter, electrodes, and cables.
Considerations for electrode types and avoiding noise in measurements.
Equipment for DC Resistivity Surveys
Describes resistivity soundings for depth variations and profiles for lateral variations.
Explains how each survey type detects geologically relevant structures.
(Soundings and Profiles)
Wenner survey and Schlumberger survey techniques.
Uses and interpretations for different electrode placements.
Resistivity Soundings
Explains log-log plots for resistivity data and their interpretation.
Importance of log-distance schemes for data acquisition.
Electrode Spacings and Apparent Resistivity Plots
Details resistivity surveys for identifying vertical structures.
Determining electrode spacings based on underlying structures.
Resistivity Profile
Defined empirical relationship between current and voltage.
Established Ohm’s Law for conductive materials.
Georg Ohm’s Contributions
T or F: resistivity as a geometrically-independent measure
T
is defined as the resistance in the wire, times the
cross-sectional area of the wire, divided by the length of the wire.
Resistivity
T or F: High values of resistivity imply
that the material making up the wire is very resistant to the flow of electricity.
T
Measured resistivities in Earth materials are primarily
controlled by the movement of
charged ions in pore fluids
Passive or Active: DC Resistivity
Active
Passive or Active: Induced Polarization
Active
Passive or Active: Self Potential
Passive
Passive or Active: Electromagnetic
Active
Active ot Passive: Magnetotelluric (MT)
Passive
Resistivity Soundings detect ______ in resistivity
depth variations
esistivity Profiles detect _____
lateral variations
Conducted using Wenner or Schlumberger survey types.
Vary electrode spacings to assess depth variations in resistivity
Resistivity Soundings
Detect lateral variations with fixed electrode spacings.
Used for identifying lateral changes like vertical faults
Resistivity Profiles
(a device for measuring electrical current)
Ammeter
Surveys
that are designed to determine resistivity variations with depth above some fixed surface location are referred to as
Resistivity Soundings
The most time effective in terms of field work is referred to as a
Schlumberger survey
the geometry of electrode placement is referred to as a
Wenner Survey
the two current electrodes (green) and the two potential
electrodes (red) are still placed in line with one another and centered on some location,
but the potential and current electrodes are not placed equidistant from one another.
Schlumberger Array
T or F: Traditional plots emphasizes important data at smaller electrode spacings (< 50 meters).
F
T or F: Log-log plots decreae visibility of smaller electrode spacing data, facilitating analysis.
F
______in log distance, providing well-sampled transition between resistivity extremes.
Evenly spaced
i. Resistivity soundings interpreted for horizontally stratified structures ii. profiles for vertical structures.
Both are true
Profiles identify can identify ______ indicating vertical contrasts in resistivity.
discontinuities
Perform soundings on both sides of the vertical structure to interpret depth variation and set profile spacing.
Soundings Analysis:
