Note Outline: Geophysical Surveying Using DC Resistivity

Introduction

• Active and Passive Geophysical Methods
• Advantages and Disadvantages of Each Method
• Electrical Methods Overview

Resistivity Basics

• Current Flow and Ohm's Law
• The Fundamental Electrical Property is Resistivity, NOT Resistance
• Resistivities for Common Earth Materials
• Current Density and Electric Field
• A First Estimate of Resistivity
• Current Flow From Two Closely Spaced Electrodes
• A Practical Way of Measuring Resistivity

Resistivity Surveys and Geology

• Sources of Noise
• Depth of Current Penetration Versus Current Electrode Spacing
• Current Flow in Layered Media
• Variation in Apparent Resistivity: Layered Versus Homogeneous Media
• Current Flow in Layered Media Versus Electrode Spacing
• A Second Example of Current Flow in Layered Media

Resistivity Equipment and Field Procedures

• Equipment
• Survey Types Overview: Soundings and Profiles
• Soundings: Wenner and Schlumberger
• Electrode Spacings and Apparent Resistivity Plots
• Advantages and Disadvantages of Each Survey Type
• Profiles

Interpretation of Resistivity Measurements

• Apparent Resistivity Curves for Soundings Over One-Layered Media
• Apparent Resistivity Curves for One-Layered Media: Part 2
• Apparent Resistivity Curves in Two-Layered Media
• Two-Layered Media: Another Example