1) The document discusses tectonic plate boundaries and continental rifting. It includes maps and figures showing crustal thinning and changes in seismic velocities at sites of active continental rifting. 2) Continental rifting occurs due to thinning of the crust and mantle upwelling at the boundaries between diverging tectonic plates. Over time, rifting can develop into a new ocean basin. 3) Examples of locations undergoing active continental rifting mentioned include the Gulf of California, Death Valley, and the East African Rift. Maps show associated crustal thinning and changes in seismic properties at these sites.

1. Introduction to Geophysics Ali Oncel [email_address] Department of Earth Sciences KFUPM Tectonic Interpretation of Seismic Refraction Profiles Introduction to Geophysics-KFUPM

2. Previous Lecture Hidden Layers Problem Situations Low Velocity layer (V 2 <V 1 <V 3 ) Thin layer (V 3 >V 2 >V 1 but h2 very small) Velocity Inversion-Hidden Layers Dipping Layer Refractions Single Dipping Refractor Surface Introduction to Geophysics-KFUPM

3. A ray incident on a surface results in 3 reflected and refracted rays. If the seismic velocities in medium 1 are α=6.0 km/sec, β=3.5 km/sec, what are the seismic velocities in medium 2? What type of material is medium 2? Identify rays #1, #2, #3, #4 as P or S waves. Solutions of Quiz 2: Question 1 Introduction to Geophysics-KFUPM

4. You are designing a refraction survey of a region where the structure is Since the refracted ray is only well recorded when it is the first arrival, how long must the line be to record the Moho refraction? At this distance what is the arrival time of the refracted ray? The direct ray? Reflected ray? Solutions of Quiz 2: Question 2 Introduction to Geophysics-KFUPM

5. Solutions of Quiz 2: Question 2 Introduction to Geophysics-KFUPM In order for the refracted ray to be the first arrival, the line must be longer than the critical distance. i c

6. Parks and Plates ©2005 Robert J. Lillie Plate Boundaries Introduction to Geophysics-KFUPM

7. Introduction to Geophysics-KFUPM A. Jon Kimerling Parks and Plates ©2005 Robert J. Lillie Raised Relief Map of North America and Adjacent Oceans

8. Introduction to Geophysics-KFUPM Due to shallow hot mantle Due to cold lithospheric plate Map of P-wave Velocity (km/s)

9. Parks and Plates ©2005 Robert J. Lillie Active Continental Rifts Advanced Rifting (Lower Elevations) Early Rifting (Higher Elevations) Introduction to Geophysics-KFUPM National Park Lands

10. Introduction to Geophysics-KFUPM Map of P-wave Velocity (km/s)

11. Introduction to Geophysics-KFUPM Continental rifting Thin crust. Map of Crustal Thickness (km)

12. Parks and Plates ©2005 Robert J. Lillie Crustal Thinning at Continental Rifts Introduction to Geophysics-KFUPM

13. Crustal Thinning at Continental Rifts Parks and Plates ©2005 Robert J. Lillie Grand Teton National Park, Wyoming Great Basin National Park, Nevada Introduction to Geophysics-KFUPM

14. Crustal Thinning at Continental Rifts Parks and Plates ©2005 Robert J. Lillie Introduction to Geophysics-KFUPM

15. Parks and Plates ©2005 Robert J. Lillie Sagauro National Park, Arizona Death Valley National Park, California Crustal Thinning at Continental Rifts Introduction to Geophysics-KFUPM

16. Parks and Plates ©2005 Robert J. Lillie Crustal Thinning at Continental Rifts Introduction to Geophysics-KFUPM

17. Parks and Plates ©2005 Robert J. Lillie Salton Sea Gulf of California Crustal Thinning at Continental Rifts Introduction to Geophysics-KFUPM

18. Continental Rifting eventually open an Ocean Basin Parks and Plates ©2005 Robert J. Lillie Introduction to Geophysics-KFUPM

19. Parks and Plates ©2005 Robert J. Lillie Continental Rifting eventually open an Ocean Basin Introduction to Geophysics-KFUPM

20. Parks and Plates ©2005 Robert J. Lillie Continental Rifting eventually open an Ocean Basin Introduction to Geophysics-KFUPM

21. Parks and Plates ©2005 Robert J. Lillie East Pacific Rise Mid-Atlantic Ridge A Continental Rift can be Viewed as the On-land Continuation of a Mid-Ocean Ridge Introduction to Geophysics-KFUPM

22. Parks and Plates ©2005 Robert J. Lillie Basin and Range Province East Pacific Rise Mid-Atlantic Ridge Gulf of California A Continental Rift can be Viewed as the On-land Continuation of a Mid-Ocean Ridge Introduction to Geophysics-KFUPM

23. Parks and Plates ©2005 Robert J. Lillie Active Continental Rifts Death Valley Salton Sea Introduction to Geophysics-KFUPM National Park Lands

24. Moho DEPTH relate to tectonic history? Introduction to Geophysics-KFUPM Fig.4.17 of Lillie

25. Introduction to Geophysics-KFUPM Fig 4.18 of Lillie

26. Formation of Oceanic Crust Introduction to Geophysics-KFUPM Parks and Plates ©2005 Robert J. Lillie

27. DIVERGENT PLATE BOUNDARY DEVELOPMENT Introduction to Geophysics-KFUPM Parks and Plates ©2005 Robert J. Lillie

28. Ocean/Continent Subduction Zone Introduction to Geophysics-KFUPM Parks and Plates ©2005 Robert J. Lillie

29. Introduction to Geophysics-KFUPM Fig 4.19 of Lillie

30. Continental Rifting eventually open an Ocean Basin Parks and Plates ©2005 Robert J. Lillie Introduction to Geophysics-KFUPM

31. CONVERGENT PLATE BOUNDARY Subduction Zone Introduction to Geophysics-KFUPM Parks and Plates ©2005 Robert J. Lillie Accretionary Wedge Volcanic Arc

32. CONVERGENT PLATE BOUNDARY Continental Collision Introduction to Geophysics-KFUPM Parks and Plates ©2005 Robert J. Lillie

33. Problems 4-3, 4-5, 4-6, 4-7 Homework due to Next Wednesday Introduction to Geophysics-KFUPM