Post on 25-Dec-2015
transcript
Note: at this point, the wave hits an “edge” from it’s perspective.
This is where the “diffracted” term comes from
Instrument response?
Seismic wave velocities• Wave equation:
– Part 1: • Force = stress x area
– Part 2: • Force = mass x
acceleration
• Also need:– Hooke’s law:
• F = -k x
• Deep breath (lower stress)…..
Deriving wave equation1. Go over some tools
2. Relate stress and displacement
3. Simplify as much as possible
4. Substitute into F=ma equation
5. Apply some vector identities
6. Show that there are only two solutions, which have the
velocities of the P- and S- waves
Stress & Strain
• Stress– Force/unit area
• Strain (1-dimension)– Here = L/L– Finite strain
• Whole history• >few %• Shape/relationships
change
– Infinitesimal strain• Less than few %• Allows some simplifications
(L’-L)/L = L/L = xx=dux/dx
Vector fields
• Divergence of a vector field:– No rotation– Just volume change– Which body wave?
Vector fields
• Curl:– No volume change– Just rotation– Which body wave?