Seismic Waves-2

1. Introduction to Geophysics Ali Oncel [email_address] Department of Earth Sciences KFUPM Seismic Waves (Continue)

2. Previous Lecture What is Seismic Wave? Waves in a Pound Sound Wave Analogy What is Wave? Wave Terminology Wavelength and Period Wave Speeds Sources of Seismic Waves Multiple Frequency Signals What is Elastic Behavior? Ductile Deformation Brittle Deformation Ductile/Brittle Behavior through the Lithosphere and Asthenosphere Elastic Constants Bulk Modules Shear Modules Poisson Ratio Typical Values of Elastic Constants for Selected Materials Body Waves Surface Waves

3. Particle Motions of Body Waves

4. 3D Components of Waves

5. 3D Components of P-wave 6.27

6. 3D Components of S-wave 6.35

7. Types of Surface Waves

9. Where  are the Lamé coefficients and  is Seismic velocities P wave velocity α and S wave velocity β depend on physical properties of medium through which they travel: Question: How  and  depend on density  ?  = k - = 2   E 3 ( 1 +  ) ( 1 - 2  ) V =  = = k + ( )   + 2    p 4/3 V =  =   s

10. Elastic Coefficients and Seismic Velocities

13. Nafe-Drake Curve L=limestone; Q=quartz; Sh=shale; Ss=sandstone. Sediments and sedimentary rock Igneous and metamorphic rock Figure 3.10 of Lillie, 1999, modified from Birch, 1960

16. Velocity-Geology Grifts and King, 1981

17. Maximum amplitude of particle motion occurs along the 90 degree phase wave front. Other wave fronts correspond to positions where the wave goes from positive to negative amplitude (180 degree) and at the minimum amplitude (270). Amplitude Changes of Particle Motion

18. Raypaths thus bend (refract) as velocity changes. Seismic energy travels along trajectories perpendicular to wave fronts. Initial wavefronts for compressional (P),shear (S), and Rayleigh ( R ) waves. Changes in velocity cause segments of wave fronts to speed up or slow down, distorting the wave fronts from perfect spheres. Wave Fronts and Raypaths

19. Seismic waves radiating from a source to one receiver. Seismic trace recording ground motion by the receiver, as a function of the travel time from the source to the receiver. For controlled source studies (seismic refraction and reflection), the travel time is commonly plotted positive downward. Seismic Trace

21. Questions?