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Applied Magnetics - Geosciences 439
Tectonics, Structure, and Exploration
Spring 2013
Professor: Steve Sheriff

Grading: Based on exams, problem sets, project reports, participation (on grading papers).
The syllabus and the ad for the course provide some direction on content
and your responsibilities.


 

Getech: processing and interpretation
Free data (US-geonet, Canada)
Blakely: Potential Theory (excerpts) Equipment Setup & Use;Handouts & Tips
USGS Potential Field Software (DOS, Oasis Montaj) How magnetometers work from GEM
Scientist's & Engineer's Digital Signal Processing Bibliography: Separation, Edge Detection, Depth

 

Spring Semester 2013:

1/30/2013: Introduction to the course, general concepts, basic Earth parameters; Montana geologic map.kmz (as .zip), aeromagnetic, combo - geology & magnetics). The shape of the Geomagnetic field (declination, inclination, magnetic elements, bar magnets).

2/1: Structure demo:(kmz: 1, 2; wmv); magnetic units (1, 2), bar magnets and the fluxgate demo. The geocentric axial dipole hypothesis, secular variation.

2/6: Magnetic potential, and the uniformly magnetized sphere (spherical coordinates, dv). The dipole equation - the fundamental equation of paleomagnetism.

2/8: More on the uniformly magnetized sphere and its flux pattern (Butler's derivation and a Geomagnetic Field applet). Inclination versus latitude(graph, map), early paleomagnetism excerpt: Collinson & Runcorn, 1960. Apparent polar wander paths and calculating them.

2/13: Problem set for next Wednesday. Stereonets, then spherical trig (see Butler's appendix) and solutions for the distance between two points on a sphere, epicenter determination, apparent pole positions, and the calculation of apparent pole positions; Pole to field mapping (D, I) <--> VGP. (web bonus: dot product).

2/15: Self assessment - these abstracts should make sense: translations and rotations (1, 2, 3). APW paths, transforms (1, 2), 2D tectonics, relative velocity vectors. More transform faults (Isacks_Oliver_Sykes), Euler poles, YouTube San Andreas.

2/20: Discuss problem set, vector review, poles and apparent polar wander, hot spot tracks (1,2), hotspot reference frame(2),

2/22: My VGP spreadsheet; True polar wander(1, 2) and paleomagnetic Euler poles (figure 1, 2).

2/27: Assignment for 3/6: an Euler pole problem (the spreadsheet, Solver demo, xls); local paleomagnetic examples (Doughty, Jolly, Brunt, Sheriff).

3/1: Continue local paleomagnetic examples (Doughty, Jolly, Brunt, Sheriff). Begin Curie temperature, magnetic minerals,

Assignment & self assessment for 3/13:

1. Find and read a structure/tectonics paper that uses paleomagnetism to measure local rotations, distributed deformation, or apparent polar wander paths. Prepare a 10 minute (+/-) presentation of this paper to share in class. Your presentation outline: authors, problem addressed, methods, results, your thoughts; put pertinent slides in powerpoint. You can find papers which reference others (e.g. Doughty & Sheriff, Jolly & Sheriff, Sheriff, Gunderson & Sheriff) by using cited reference search in the Mansfield Library’s Web of Knowledge/Web of Science multidisciplinary index. I'll listen for your understanding of paleomagnetism.

3/6: Blocking temperatures, thermal magnetic cleaning, and a quick look at vector end point diagrams (vector mixing, components).

3/8: Hysterisis, coercive force, magnetic domains, and AF cleaning.

3/13: My APW answers; your presentations of structure/tectonics papers that use paleomagnetism.

3/15: Midterm

3/20: Midterm return: do as take home for scores below 40 - due Friday 3/22. Magnetic exploration, anomalies with latitude. Buried dipole applet & NW Montana. Magnetic prospecting; Montana aeromagnetics (with geology, data, grid). Total field (scalar) anomalies, fluxgate, proton precession (2) and cesium vapor magnetometers - details from GEM Systems. Block models (pblock, pdike) relating magnetics and gravity.

3/22: Discuss midterm and more exploration; block models (pblock, pdike), simple models (from Berkeley) relating magnetics and gravity; Poisson's relation the Talwani algorithm, MAGCAD in DOSBOX (mount c c:\), and forward models. Software: pblock, pdike, (Cooper's Software, mine), experimental design.

3/27: Experimental design, sampling theorem (2) and a start on Fourier analysis and frequency filtering; (demo.ppt). Some good definitions & explanations: Fourier series and transforms; pretty good web 'book' on geophysical signal analysis.

3/29: Fourier series & Fourier transform (Fourier series applet - applied to high frequency filtering; Fourier transform applet) white noise (1/f^o), instrument precision, designing filters in the frequency domain - high pass, low pass, bandpass, notch, and threshold. 2D FFT applet; magnetics of a randomly magnetized layer (filter shape, with depth, radial averages {you could compare pblock}.

4/3 - 4/5: Spring Break

4/10: Again: 2D power/amplitude spectra, white noise (1/f^0), signal/noise, and signal stacking.xlsx. Equivalent layers, upward continuation. Think about the shape of these things.

4/12: More upward continuation (ppt, Jacobsen.pdf, Phillips_1996) Urquhart's frequency filtering of potential fields. Gridding & contouring (figure: 4 methods) with Surfer; the USGS extensions to Oasis Montaj.

4/17: Your turn: Separation filtering - with upward continuation (stone ring photo, data).

4/19: Reduction to pole (RTP with latitude, Blakely excerpt); pseudogravity (Blakely excerpt; Chicxulub 2010 (ref)). Public data (Geonet; MT_Geol.kmz; NW_Montana (dat, grd, kmz); Beaverhead (mag, grav);

Assignment: data, Oasis Montaj, and the USGS extensions for continuation - due 4/26.
  • Choose one of the Montana data sets (NW_MT, NC_MT, SW_MT) and use Surfer to experiment, grid, and visualize the data appropriately. Alternatively, choose an area in the US or Canada in which you are more interested. If you do this you'll need to change longitude, latitude pairs to UTM coordinate pairs; I use Corpscon.
  • Experiment with gridding, upward continuation, reduction to pole (RTP), and pseudogravity (PSG) using the USGS/Oasis Montaj package.
  • Learn to separate deeper sources from shallow sources using equivalent layers and subtracting upward continuations.
  • Put together a good, explanatory graphic presentation and email it to me.
  • Think about all this as you do it and make sure you understand what you are doing.

4/24: Montana mag, blanking files (LL, UTM)). Separation filtering: statistical methods; filter figures: random layer components, with depth, with thickness. PS-mag 2D_sequence,

4/26: Power Spectrum-mag - Calculate the depths! Spector & Grant: (1, 2). Matched filtering (step-by-step, MYAP example.ppt

5/1: Decorrugation (define); matched filtering in Oasis/USGS: demo data from Yellowstone - remember to use safe mode (F8 on boot). Compare matched filter separation to that by upward continuation.

5/3: Making matched filter choices.  Next, edge detection: first vertical and second vertical derivatives, HGM, analytic signal (low latitudes). Fabric analysis: compare 2VD, HGM, AS, TiltD; and disk w/ Montaj. Edge detection on models (ppt), using post maps for curvature maxima.

Read this for self assessment: Phillips, 1998 - it should be making sense

Edge detection: use horizontal gradient, analytic signal, and tilt derivative analysis on the TMI from a set of simulated kimberlite pipes. Separate signal and noise as best you can, comparing matched filtering with differencing upward continuations. Turn in a 2-3 page analysis (not counting color figures) of the methods with respect to these data and your thoughts on the results (due 5/8 - Wednesday). Compare methods and present informative results. Include a figure comparing (overlay) the maxima of the horizontal gradient and analytic signal on the zero contour of the tilt derivative.

5/8: Great example from Grauch. Depth estimates: slope half-slope (example). Euler deconvolution; the faulted dome (.grd) and Euler solutions on the faulted dome.ppt and some figures: 1, 2, 3. The magnetic modeling of the faulted dome comes from using models from Surfer and PFmag3D (program) from R. Blakely in the USGS DOS  software collection.

5/10: Depth estimate finale: Euler: Stevi.wmv, then Werner deconvolution: Stevi example. Depth estimates from the analytic signal and horizontal gradient. Curvature/special function depth analysis from Phillips et al., 2007 on curvature. Inverse examples: Philipsburg Batholith (Pburg.ppt, wmv, wmv2, Darby.wmv).

Tuesday May 14 - Final Exam; 3:20 - 5:20 your individual choice: Take home or in-class.

 

The Spring 2012 course

The Spring 2011 course

The Spring 2010 course

The Spring 2009 course

The Spring 2008 course.

 

 

 

 

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