305-pp2 - UNIVERSITY OF SOUTH ALABAMA Last Time Geophysics...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
1 GY 305: Geophysics GY 305: Geophysics Lecture 2: Lecture 2: Wave Theory Wave Theory - Part 2: Part 2: Refraction and Reflection Refraction and Reflection UNIVERSITY OF SOUTH ALABAMA Geophysics Introductions, class policy etc. Introduction to geophysics Start of Wave theory (properties of rocks) Last Time Last Time Geophysical analysis is done when… 1) you can’t get direct access to the rocks 2) you want to “model” a large area quickly 3) you know what you are looking for … but every geophysical technique only “estimates” geology (lots of interpretation) Geophysics There are 2 scales of geophysical analysis: 1) “small-scale” (single well; shallow penetration seismic etc.) Geophysics Geophysics 2) “large-scale” (basin wide surveys) Proposed well So what kind of geophysics is So what kind of geophysics is there? Geophysics Geophysics Seismology - Study of natural [from earthquakes] and man-induced seismic waves Gravity - Study of variations in earth's gravitational field Electrical Methods - Use of electrical conductivity / resistance of earth Electromagnetics - Study of induced electromagnetic fields Magnetics - Analysis of variations in earth's magnetic field Radioactivity - Study of natural and induced response to radioactivity ht p:/ www.laynewater.com/images/borehole_geophysics1.jpg Geophysics Geophysics Seismology - Study of natural [from earthquakes] and man-induced seismic waves Gravity - Study of variations in earth's gravitational field Electrical Methods - Use of electrical conductivity / resistance of earth Electromagnetics - Study of induced electromagnetic fields Magnetics - Analysis of variations in earth's magnetic field Radioactivity - Study of natural and induced response to radioactivity Passive methods Measuring spatial variations of static or natural fields of force static or natural fields of force Active methods Measurement of wave field characteristics (i.e. travel times of elastic waves, and amplitude and phase of electromagnetic and phase of electromagnetic waves)
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
2 Wave Theory This is complex stuff to model, so we need to make a few assumptions: 1) the media must be considered heterogeneous, but we can consider this heterogenosity to be the result of stacked horizontal layers of different homogeneous materials. Homogeneous Shale Homogeneous Sandstone Homogenesous Limestone Overall, heterogeneous Wave Theory This is complex stuff to model, so we need to make a few assumptions: 2) Seismic disturbances (natural or induced) travel by elastic displacements of the media. Lowrie, W., 2007. Fundamentals of Geophysics 2nd edition, Cambridge University Press, Cambridge, 381p Wave Theory Surface waves spread out over the surface and are analogous to ripples on the surface of a pool of water. There are 2 categories of surface wave (collectively called L-waves ): Rayleigh waves (LR) vibrate in a vertical orientation but in combination with forward propagation, forces the particles that comprise the media to move in a retrograde ellipse.
Background image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 8

305-pp2 - UNIVERSITY OF SOUTH ALABAMA Last Time Geophysics...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online