GEOL 414 Applied Geophysics Fall Semester 2006 Principles of various geophysical methods and their application to geologic problems. Prerequisites: Geology 101, Mathematics 213, Physics 204 or credits.

Applied Geophysics Textbook:Burger, Sheehan, and Jones, Introduction to Applied Geophysics, 2006, W.W. Norton & Co. Inc., ISBN Course Goals:To give students an understanding of the physical principles of geophysical methods so that they will appreciate the strengths and limitations of the methods. After certain fundamentals have been mastered, the students study the procedures used in data acquisition and use the department's equipment to conduct geophysical surveys. The final phase of each section of the course gives students training in interpretation of geophysical data.

Geol 414 Topic Sequence Section 1 Introduction to Geophysics -Methods, Units, Applications, Geophysical Societies, Geophysical literature Section 2 Gravity fundamentals Gravity surveying Gravity data reduction and analysis Section 3Magnetic fundamentals Magnetic surveying Magnetic data reduction and analysis Section 4Combined gravity and magnetic survey field project Section 5Electrical Methods and Surveying Section 6Seismology fundamentals Section 7Refraction seismology Section 8Reflection seismology Section 9Thermal methods

American Geological Institute Index Geology Disciplines Geology Economic Geology Geochemistry Geophysics Paleontology Hydrology Soil Science Engineering Geology Oceanography Planetology

American Geological Institute Index Sub-disciplines in Geophysics General Geophysics Experimental Geophysics Exploration Geophysics Geodesy Geomagnetism & paleomagnetism Gravity Heat Flow Seismology Marine Geophysics

American Geological Institute Index Sub-disciplines in Geophysics Extraterrestrial Geophysics* Soil Physics* Mathematical Geology* Mineral Physics* Stable Isotopes*

American Geophysical Union Sections Atmospheric Sciences Biogeosciences Geodesy Geomagnetism and Paleomagnetism Hydrology Ocean Sciences Planetary Sciences Seismology Space Physics and Aeronomy Tectonophysics Volcanology, Geochemistry, and Petrology

Topics in some Geophysics Textbooks: Applied Geophysics Telford, Geldart, Sheriff Gravity Methods Magnetic Methods Seismic Methods Electrical Properties of Rocks and Minerals Natural Electrical Sources Electromagnetic Methods Resistivity Method Induced Polarization Radioactivity Method Geophysical Well Logging

Applied and Environmental Geophysics Reynolds Potential Field Methods Applied Seismology Electrical Methods Electromagnetic Methods

Gravity Units - gals 1 gal = 1 cm s -2 Absolute gravity Relative gravity Range to mgals Property of Earth – density distribution F = Gmm r -2 g = Gm r -2

Heat Flow Units – mW m -2 Q = ΛΚ Q = Q 0 + Ab A = A 0 e -z/b Range 10 3 to 0 Mean ~ 84 mW m -2 Laplace’s equation Poisson’s equation The diffusion equation

Magnetics Units – nanoTeslas nT 7 measurable components –Declination –Inclination –F (total field) –X (north) –Y (east) –Z (vertical) –H (horizontal) Coulomb’s Law Field Strength Magnetic Intensity

Magnetics Units – nanoTeslas nT Main field 60,000 to 30,000 nT –Core dynamo External field 10’s nT –Diurnal, seasonal, ionization of atmosphere solar wind currents, storms Anomalous field 1000’s nT –Magnetic susceptibility of crust

Seismology Measured units – time & distance Interpreted units – velocity Application interpretation – rock type, structure Refraction Reflection Earthquakes The Wave Equation

Resistivity Units – ohm m V = iR R = rA/L Various arrays with characteristic electrode spacing

Bouguer Gravity of the Lake St. Martin Impact Structure

Residual Gravity of the Lake St. Martin Impact Structure

Surprise Valley, California

Digital elevation model

Surprise Valley, California Bouguer Gravity contours Red lines are seismic lines Black lines are gravity profiles seen in next two slides

Surprise Valley, California

Bouguer gravity profiles

Surprise Valley, California Vertical derivative of the Bouguer gravity profiles

The Geoid

Gravity at UND The predicted gravity is given in units of 'milligals': 1 gal = 1 cm sec -2 1 kilogal = 1000 gal 1 milligal = 1/1000 gal Latitude: Longitude: MSL Height: Predicted gravity: /- 2 milligals