Earthquake Seismology: Fundementals

1. Introduction to Geophysics Ali Oncel [email_address] Department of Earth Sciences KFUPM Earthquake Seismology: Fundamentals 1

2. Fairly thick layers result in distinct events on travel time graph Seismic Waves: As Probes of Earth’s Interior Travel Time Models for FLAT EARTH

3. Travel Time Models of earthquakes for FLAT EARTH Series of thin layers results in rays that emerge at steeper angles with increasing depth . Slopes of first arrivals change with distance, indicating the changing velocities with depth.

4. Numerous layers so thin that the changing velocity with depth is modeled as a function V(Z). Deep-penetrating rays, having encountered faster velocities , emerge at steeper angles than the shallower rays. The changing wave front angles result in changing apparent velocity , evident as changing slope on the travel-time graph. Travel Time Models of Earthquakes for FLAT EARTH

5. Summary: Travel Time Models

6. Earth with constant seismic velocity (V). Ray paths are linear because no refraction occurs. The convex-upward form of the graph is simply because measurements are along Earth’s curved surface. Travel Time Models of Earthquakes for Curved EARTH

7. Rays bend away from the vertical, leading to steeper emergence angles (hence, higher apparent velocities) than for the constant velocity case in (a). Likewise, more curvature on the travel-time graph indicates higher apparent velocity than in (a). Earth model with a gradual increase in velocity with depth, V(z).

8. Selected ray paths and travel-time curves for body (P,S) and surface waves. As in (b), seismic velocities increase with depth.

9. Travel Time Models of Earthquakes for Curved EARTH

10. Questions?

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