Geol 454
Environmental and Exploration Geophysics I
Introduction tom.h.wilson
tom.wilson@mail.wvu.edu
Phone: 293-6431
Department of Geology and Geography
West Virginia University
Morgantown, WV
Tom Wilson, Department of Geology and Geography

General information - handouts
Hunting for Abandoned Wells
• Syllabus (see handout)
• Example paper summary
Hunting for caves
Tom Wilson, Department of Geology and Geography

General information
Hunting for Abandoned Wells
• Syllabus (see handout)
• Textbook (current status ?)
• Class web page
• Grading (32% (pbs),28% (labs), 10%
(paper summaries), 10% (mid term),
20% (final))
• Papers and paper summaries (see handout and link)
Hunting for caves
Tom Wilson, Department of Geology and Geography

Tom Wilson, Department of Geology and Geography

Objectives
1. Obtain conceptual knowledge of the basic theory of gravitational, magnetic, electric, and electromagnetic fields.
2. Develop an understanding of how geophysical observations can be integrated into your discipline or study.
3. Provide analytical experience necessary to oversee applications of these methods in your specialty area.
Tom Wilson, Department of Geology and Geography

Definitions
Applied Geophysics
•Making and interpreting measurements of physical properties of the earth to determine sub-surface conditions, usually with an economic objective, e.g. discovery of fuel or mineral deposits.
Environmental Geophysics
•The applications of geophysical methods to the investigation of nearsurface physico-chemical phenomena which are likely to have
(significant) implications for the management of the local environment
Sheriff, R. E., Encyclopedic Dictionary of Exploration Geophysics, SEG. &
Reynolds (1997)
Tom Wilson, Department of Geology and Geography

• Terrain Conductivity
• Resistivity
• Gravity
• Magnetics
These methods represent only a few of the various geophysical methods used to peer beneath the surface in a
Tom Wilson, Department of Geology and Geography manner.

Terrain Conductivity
Inducing current flow – action at a distance
Tom Wilson, Department of Geology and Geography

Terrain Conductivity Instrumentation
Active Source
EM31
EM34
Two Commonly used Terrain Conductivity Meters -
You’ll hear a lot about these in the first 3-4 weeks of the class
Tom Wilson, Department of Geology and Geography

Multifrequency terrain conductivity meter-
Same idea
Tom Wilson, Department of Geology and Geography

Applications
Contaminant Plumes
Tom Wilson, Department of Geology and Geography
Metal Detection

Abandoned mine lands and mine spoil
Tom Wilson, Department of Geology and Geography

Tom Wilson, Department of Geology and Geography

Tom Wilson, Department of Geology and Geography

Other kinds of instrumentation
Gem2 – Aeroquest/GeoPhex http://www.terraplus.ca/products/electromagnetics/gem2.htm
Tom Wilson, Department of Geology and Geography

Active source
Resistivity
Case Histories
TerraPlus http://www.terraplus.ca/case-histories/index.html
Tom Wilson, Department of Geology and Geography

Resistivity applications
Map is contoured in units of 0.5 percent change, which is a measure of the drop in apparent resistivity from the baseline data set to the data collected after 69 gallons of solution was released. The largest observed percent change in the data was 0.2%, concentrated near the northeast margin of the tank, and beneath the center of the tank.
Underground Storage Tanks
Leak detection (TerraPlus)
WESTEC Case Study
Tom Wilson, Department of Geology and Geography

Tom Wilson, Department of Geology and Geography

Resistivity measurements made below the liner system
Landfill Leak Detection http://www.terraplus.com/papers/henderson.htm
A typical response to an introduced leak is shown on in the figure. This calibration demonstrated that the sensitivity of the particular system was approximately 20 gallons in total introduced leachate, and the location ability of the software was within 10 to 20 feet. This 20-gallon detection level is equivalent to a 4-foot-square zone of saturated soil, assuming a 1-foot thickness.
Tom Wilson, Department of Geology and Geography

Gravitational fields
Passive source
LaCoste Romberg Gravimeter
Tom Wilson, Department of Geology and Geography
Worden Gravimeter

From Hooke’s Law F
 kx we get g
 kx m s x
 m s g k
Colorado School of Mines web sites -
Mass and spring
Pendulum measurement x spring extension m s spring mass k Young’s modulus g acceleration due to gravity
Tom Wilson, Department of Geology and Geography

Newton’s Universal Law of Gravitation
F
12

G m
1 m
2 r
2
12
F
12
Force of gravity
G Gravitational Constant r
12 m
2 m
1
Newton.org
Tom Wilson, Department of Geology and Geography

We are interested in g object
: some subsurface feature like karst systems, bedrock configuration and groundwater accumulations g
E

F
12 m s

G m
E
R
2
E m s spring mass m
E mass of the earth
R
E radius of the earth g
E represents the acceleration of gravity at a particular point on the earth’s surface. The variation of g across the earth’s surface provides information about the distribution of density contrasts in the subsurface since m =

V (density x volume).
Tom Wilson, Department of Geology and Geography

Comparison of bedrock depth map to the residual gravity map
Form Stewart
Tom Wilson, Department of Geology and Geography
Residual gravity map

Magnetic Methods
Passive source
Magnetic Elements for your location http://www.ngdc.noaa.gov/geomagmodels/IGRFWMM.jsp
Today’s Space Weather http://www.swpc.noaa.gov/
Tom Wilson, Department of Geology and Geography

Proton Precession Magnetometers
Tom Boyd’s Introduction to Geophysical Exploration Course http://www.earthsci.unimelb.edu.au/ES304/index.html
Tom Wilson, Department of Geology and Geography

See http://www.earthsci.unimelb.edu.au/ES304/MODULES/MAG/DESIGN/MagForwardJava.html
Tom Wilson, Department of Geology and Geography

Field Operation
Tom Wilson, Department of Geology and Geography
Coal mine refuse area

Magnetic monopoles
F m 12

1
 p
1 p
2 r
2
12
F m12
Magnetic Force

Magnetic Permeability p
1 and p
2 pole strengths p
2 r
12 p
1
Coulomb’s Law
Tom Wilson, Department of Geology and Geography

Magnetic Monopoles do not exist. The fundamental magnetic element is a dipole or combination of one positive and one negative magnetic monopole.
Tom Wilson, Department of Geology and Geography

Looking for abandoned wells
Critical to EOR, EGR, CO2 Sequestration, fracking and frack water storage and disposal
Tom Wilson, Department of Geology and Geography
From Martinek

7000 gamma anomaly
No excavation planned since the anomaly is located adjacent to a water main
From Martinek
Tom Wilson, Department of Geology and Geography

Start reading chapter 8
Visit class page at http://www.geo.wvu.edu/~wilson/geol454.htm
For general background on electromagnetic methods read pages 499 through 514 .
Most of our work will concentrate on concepts associated with “non-contacting ground conductivity measurements” pages 514 – 518 .
Tom Wilson, Department of Geology and Geography

Also look over McNeill’s technical note on EM
Conductivity/Low induction number
Both readings are linked on lecture 1 – see class web page at http://www.geo.wvu.edu/~wilson/geol454.htm
We will begin discussing basic terrain conductivity theory on Thursday
Tom Wilson, Department of Geology and Geography

Any questions?
If you are taking the writing section, please remain for a few minutes so we can have a brief discussion and answer any basic questions you may have.
Tom Wilson, Department of Geology and Geography

Writing Section – please remain after class
Read through the handout with brief question/answer session.
Writers should start working on their first paper this week.
Tom Wilson, Department of Geology and Geography