2nd Year: Geophysical Methods in Geology

Trinity Term 2006

  • Week 2 :

    • Tues. 10-11 Lecture 1 : Gravity [ABW]
    Gravitational acceleration and potential. Units. Gravity and potential of an ellipsoid of revolution. Gravity, potential and mass distributions in the Earth. Rock densities. The geoid.
    Frid. 10-11 Lecture 2 : Gravity [ABW]
    Absolute and relative gravity instruments. Definition of gravity anomaly. Free-air and Bouguer reductions. Gravity anomalies over granites, sedimentary basins and basic igneous intrusions. Regional background fields.
    Frid. 11-1 Practical 1 : [ABW]
    Interpretation of Bouguer gravity anomalies over the Pennines

  • Week 3:

    • Tues. 10-11 Lecture 3 : Magnetics [ABW]
    Magnetic force and potential. International Geomagnetic Reference Field. Instruments, data corrections, survey design.

    The Mendips Field Trip will take place during Wednesday to Sunday, May 10-14th. Group 1 will leave Wednesday and return Friday. Group 2 will leave Friday and return Sunday. Undertake gravity, magnetic and seismic measurements in the Mendip Hills [ABW, CM, PJ, MW, MR].


  • Week 4:

    • Tues. 10-11 Lecture 4 : Magnetics [ABW]
    Time variations, external and internal sources. Origin of the Earth's field, Induced and remanent magnetism, susceptibility. Magnetic anomalies over dykes.
    Frid. 10-11 Lecture 1 : Seismic refraction [MW]
    Instruments and survey design. Travel-time distance graphs. Interpretation of layer thickness and velocities. Dipping layers, hidden layers, time term method.
    Frid. 11-1 Practical 2 : [ABW]
    Interpretation of magnetic anomalies over the Cleveland dyke
    Measured total magnetic field over the Cleveland dyke

    Measured (smoothed) magnetic anomalies over Beacon Hill, Mendips

  • Week 5:

    • Tues. 10-11 Lecture 2 : Seismic reflection [MW]
    Instruments and survey design. Shot gathers and Common Depth Point (CDP) stacks. Velocity analysis. Normal Moveout. Multiples.
    Frid. 10-11 Lecture 1 : Electrical and electromagnetic methods [MW]
    The resistivity of rocks. Electrode arrays and apparent resistivity. Resistivity data interpretation. Pseudo-sections. Self potential (SP).
    Frid. 11-1 Practical 3 : [MW].
    Reflection seismic data processing

  • Week 6:

    • Frid. 10-11 Lecture 2 : Electrical and electromagnetic methods [MW]
    Induced polarisation (IP). Time and frequency domain IP methods. Basic principles of electromagnetic prospecting. Tilt-angle, phase and VLF methods.
    Frid. 11-1: Mendips geophysical data processing and reduction [ABW, MW]

  • Week 7:

    • Mendips geophysical data processing and reduction [ABW, MW]
    Project report - Guidelines

    Topography of the Beacon Hill region with summary geology overlay
    Aerial photo of the Beacon Hill region

    Group 2 - Waggon & Horses

    Gravity - All data - Group 1 + Group 2
    Bouguer anomaly profile to the north and south of the Waggon & Horses
    Trial model for grav2dc

    Magnetics - Raw Data May 12-13
    Magnetics - Raw Data May 14
    Magnetics Merged position + Profile data - May 11-12 Profiles 1-5
    Magnetics Merged position + Profile data - May 13-14 Profiles 3-10
    Magnetics xyz data (for contouring)
    Preliminary contour map + outcrop of Andesite (from Hancock)
    Magnetic anomaly profile between the Waggon & Horses and Fosse Way from the 2002 survey
    Trial model for mag2dc

    Seismic and Electrical data

    Reading :

    "An introduction to geophysical exploration" by P. Kearey and M. Brooks. Blackwell Science. 254pp.
    Highly recommended. Chapters 2-7 are particularly relevant to the course. Includes problem sets.

    "An introduction to seismic interpretation" by R. McQuillin, M. Bacon and Barclay : Graham & Trotman.
    A good supplmentary text for seismic reflection.

    "Looking into the Earth: An introduction to Geological Geophysics" by A. E. Mussett and M. A. Khan. Cambridge University Press. 470pp.
    Recommended. Probably the best introduction to "geological geophysics" around at the moment. Chapters 2-3, 6-7, 8, 11 are particularly relevant to the course. Includes problem sets.

    "Fundamentals of Geophysics" by. W. Lowrie. Cambridge University Press, 1997.
    A good supplementary text for magnetics.

    Lacoste-Romberg land gravimeter
    Gravity base Stations in the UK
    SmartSeis seismic reflection and refraction
    IGRF Geomagnetic Field Model (1945-2005)
    BGS hourly means of total magnetic field in the UK
    GARMIN 12XL GPS Receiver

    Oxford Marine Geophysics (Gravity, Magnetics, Seismic) Group
    Oxford Paleomagnetics Group

    Society of Exploration Geophysicists (SEG)
    SEG Gravity and Magnetics Committee - includes useful glossary of potential field terms
    Example of a Gravity and Magnetics consultancy - includes a "primer on gravity and magnetics

    Department of Earth Sciences Home Page

    Tony Watts - Last modified : April 25th, 2006