1. Geophysics/Tectonics
GLY 325

2. The Wave Equation Modeled
Even for models with no noise, identifying phases may be challenging. However, you can train your eye/brain to learn how to do this.

3. The Wave Equation Modeled
You will learn to do this...

4. The Wave Equation Modeled
So, at any interface, some energy is reflected (at the angle of incidence) and some is refracted (according to Snell’s Law). Let’s look at a simple model and just watch what happens to the P-wave energy...

5. Refraction Interpretation
We’ll no look specifically at refractions and discuss interpretation. First, let’s look at something beyond the two-layer case.

6. Multilayer Model Distance Time Direct Wave 1st Layer Refraction
2nd Refraction
1st Reflection
2nd Reflection

7. Multilayer Model
Prior to the first arrivals, only background noise interferes. After the first arrivals, background noise plus many other phases are recorded.
Distance
Direct Wave
1st Layer Refraction
Time
2nd Refraction

8. Case Studies
Why is determining depths to interfaces and seismic propagation velocities important?
(1) Depth to the Moho (crust/mantle boundary) often relates to tectonic history:
• Thin crust at rift zones and mid-ocean ridges
• Thick crust at mountain ranges
•Thin to thick transition at continental margins
(2) Velocity of upper mantle (lower lithosphere) suggests asthenospheric upwelling:
• Low seismic velocity means hot asthenosphere is shallow and partial melting occurs (continental rifts & mid-ocean ridges)
• Higher seismic velocity means no asthenospheric upwelling.

9. Global Crustal Thickness (km)
Case Studies
Global Crustal Thickness (km)

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12. Global Geologic Province
Case Studies
Global Geologic Province

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