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    Applied geophysics Introduction

    Techniques and targetsIntroduction to geophysical methods:

    Reference:Sharma p1-10Reynolds p1-27

    Applied geophysics Introduction

    What do we mean by applied geophysics?

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    Applied geophysics Introduction

    Remote sensingConstraining the Earths sub-surface with observations at the surface

    Geophysical techniques measure physical phenomena: Gravity Magnetism Elastic waves Electricity Electromagnetic waves

    Which are sensitive to sub-surface physical properties: Density Magnetic susceptibility Seismic wave velocity and density Resistivity Conductance/inductance/permitivity

    Oh, and its relatively cheap

    Applied geophysics Introduction

    Active and passive

    ActiveTransmit a signal into the subsurface and record what comes back

    Seismic arrival explosions Electrical current Electromagnetic waves

    PassiveMeasure naturally occurring phenomena

    Gravity field Magnetic field Seismic arrivals - earthquakes

    think scale

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    Applied geophysics Introduction

    Our scalemeters to kilometers

    The techniques well talk about are used in the fields of

    Environmental geophysics

    Engineering geophysics

    Exploration geophysics

    Applied geophysics Introduction

    Planning a survey

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    Applied geophysics Introduction

    Target identification

    Applied geophysics Introduction

    MagneticsExamples

    Main use: locating steel drums and pipes

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    Applied geophysics Introduction

    ExamplesSeismic reflection

    Applied geophysics Introduction

    Seismic reflectionExamples

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    Applied geophysics Introduction

    Ground penetrating radarExamples

    Applied geophysics Introduction

    Ground penetrating radarExamples

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    Applied geophysics Introduction

    Techniques and targets

    mmPPsResistivityMagneto-telluric

    PPPsPPPmPermitivity, conductivityEM Ground penetrating radar

    mmsssmPmmConductance, inductanceEM - VLF

    mPPPPPPPPsConductance, inductanceElectromagnetic (EM)

    mmmmmsmPmmResistivity, capacitanceInduced polarization

    mmmPmPPotential differencesSpontaneous potential

    mPsPPPPPmmResistivityResistivity

    mssmPPElastic moduli, densitySeismic reflection

    ssPmPPElastic moduli, densitySeismic refraction

    PPmsPPPSusceptibilityMagnetic

    sssssPPDensityGravity

    Dependent physical property

    Geophysical Method

    Hyd

    roca

    rbon

    exp

    lora

    tion

    (coa

    l, oi

    l, ga

    s)

    Reg

    iona

    l geo

    logi

    c st

    udy

    (>10

    0s k

    m2)

    Expl

    orat

    ion/

    deve

    lopm

    ent

    of

    min

    eral

    dep

    osits

    Engi

    neer

    ing

    site

    in

    vest

    igat

    ions

    Hyd

    roge

    olog

    ical

    inve

    stig

    atio

    ns

    Det

    ectio

    n of

    sub

    surf

    ace

    cavi

    ties

    Map

    ping

    leac

    hate

    and

    cont

    amin

    atio

    n pl

    umes

    Loca

    tion

    of b

    urie

    d m

    etal

    lic

    obje

    cts

    Arch

    aeog

    eoph

    ysic

    s

    Fore

    nsic

    geo

    phys

    ics

    P primary method; s secondary; m maybe sometimes

    Applied geophysics Introduction

    Profiling vs. mappingWhat is the nature of the target?

    2D or 3D?

    Preliminary site evaluation necessary?

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    Applied geophysics Introduction

    Station spacing

    Must ensure that spacing is sufficient to sample anticipated signal

    Applied geophysics Introduction

    Limitations

    Methods require contrast in physical properties

    Nonuniqueness

    Direct modeling: calculate the result of a specific structure

    Inverse modeling: determine the causative structure from observations usually ambiguous

    e.g. small shallow body vs. large deep body

    Resolution is determined by the wavelength of the signal

    sesimic: km, radar: cm

    Noise prevents recovery of low amplitude signal

    e.g. wind, traffic, water pumps, power lines

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    Applied geophysics Introduction

    Multiple methodsto improve uniqueness and cross-check interpretations

    Applied geophysics Introduction

    Introductions

    Instructors:

    Richard AllenRm 106 Weeks Hall; Tel: 262-7513; [email protected]

    Dante FrattaRm 2258 Engineering Hall; Tel: 265-5644; [email protected]

    Teaching Assistant:

    Mei XueRm 111 Weeks Hall; 262 9784; [email protected]

    Office hours: by appointment

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    Applied geophysics Introduction

    Sources

    Course webpage: http://www.geology.wisc.edu/courses/g594/

    - lecture notes, homeworks etc

    Required text

    Environmental and Engineering Geophysics, 1st ed, Sharma, 1997

    Other reference texts

    An Introduction to Applied and Environmental Geophysics, Reynolds, 1997.

    Applied Geophysics, 2nd ed, Telford, Geldart, Sheriff, 1990

    Exploration geophysics of the shallow subsurface, Burger, 1992.

    Whole Earth Geophysics, Lillie, 1999.

    An introduction to geophysical exploration, Keary, Brooks and Hill, 2002

    Applied geophysics Introduction

    Grading

    50% - Homework: Bi-weekly problem sets

    10% - Quiz 1 October 7th

    15% - Quiz 2 November 23rd

    25% - Final December 17th 12:25pm

    Announcements of any changes will be made at the lectures and on the webpage.

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    Applied geophysics Introduction

    Topic schedule

    Weeks 1-2: Gravity Methods

    Weeks 3-4: Magnetic Methods

    Weeks 5-6: Resistivity Methods

    Weeks 7-11: Seismic Reflection and Refraction Methods

    Weeks 11-13: Electromagnetic Methods

    Week 14: Ground Penetrating Radar Methods

    Week 15: Borehole Methods

    Applied geophysics Introduction

    Additional material

    Summaries and examples of other methods

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    Applied geophysics Introduction

    GravityExamples

    Applied geophysics Introduction

    Seismic refractionExamples

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    Applied geophysics Introduction

    Electrical resistivityExamples

    Applied geophysics Introduction

    Electrical resistivityExamples

    polluted sand

    clean sand

    polluted sand

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    Applied geophysics Introduction

    Electromagnetic surveyingExamples

    Applied geophysics Introduction

    Electromagnetic surveyingExamples

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