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# ÖNCEL AKADEMİ: INTRODUCTION TO GEOPHYSICS

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Tectonic Interpretation of Seismic Refraction Profiles 2

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### ÖNCEL AKADEMİ: INTRODUCTION TO GEOPHYSICS

1. 1. Introduction to Geophysics Ali Oncel [email_address] Department of Earth Sciences KFUPM Tectonic Interpretation of Seismic Refraction Profiles Introduction to Geophysics-KFUPM
2. 2. Previous Lecture <ul><li>Hidden Layers </li></ul><ul><ul><li>Problem Situations </li></ul></ul><ul><ul><li>  Low Velocity layer (V 2 <V 1 <V 3 ) </li></ul></ul><ul><ul><li>Thin layer (V 3 >V 2 >V 1 but h2 very small) </li></ul></ul><ul><ul><li>Velocity Inversion-Hidden Layers </li></ul></ul><ul><li>Dipping Layer Refractions </li></ul><ul><ul><li>Single Dipping Refractor Surface </li></ul></ul><ul><li>Quiz </li></ul>Introduction to Geophysics-KFUPM
3. 3. Δ X=10 m <ul><li>Can you pick out the direct arrival? </li></ul><ul><ul><li>A= Direct Arrival, t A1 =0.003 sec, t A2 ………… </li></ul></ul><ul><ul><li>Can you pick out the refraction arrivals? How much critical refraction is there? 2 Critical Refractions: B and C </li></ul></ul><ul><ul><li>t B1 =0.01msec , t c1 =0.016 sec </li></ul></ul><ul><li>How would you determine the refraction velocity? </li></ul><ul><li>V 2 = 45m/0.007 sec =6750m/sec </li></ul><ul><li>V 3 = 148m/0.001 =14800 m/sec </li></ul><ul><li>How would you determine the air wave or direct arrival velocity? </li></ul><ul><li>V direct = 33m/0.01 sec =3300 m/sec </li></ul><ul><li>V air = 33m/0.034 sec =963 m/sec </li></ul>0.007 0.01 148 m 45 m 0.01 0.02 0.03 0.04 Introduction to Geophysics-KFUPM 0.01 Second 0.034
4. 4. <ul><li>Problem 3.2 in pp. 127 Berger's book. </li></ul><ul><li>Figure is a field seismograph from a region with horizontal interfaces. Interpret the data. </li></ul><ul><li>First geophone is at 3 meters from the source, the remainder are spaced at 10m intervals. </li></ul><ul><li>What can you see? </li></ul><ul><li>How many layers indicated by the shot record? </li></ul><ul><li>What are their velocities? </li></ul><ul><li>What are the time intercepts? </li></ul><ul><li>Determine the thickness of each layer? </li></ul>Homework due to April 15 Introduction to Geophysics-KFUPM P.C: 1 milisecond is 10^-3 seconds
5. 5. <ul><li>First geophone is at 3 meters from the source, the remainder are spaced at 10m intervals. </li></ul><ul><li>What can you see? </li></ul><ul><li>How many layers indicated by the shot record? </li></ul><ul><li>What are their velocities? </li></ul><ul><li>What are the time intercepts? </li></ul><ul><li>Determine the thickness of each layer? </li></ul>Problem 3.3 in pp. 127 Berger's book. Using the information in Figure, determine as much as possible about the subsurface geology at the site where the information was recorded. Homework due to April 15 Introduction to Geophysics-KFUPM P.C: 1 milisecond is 10^-3 seconds
6. 6. Parks and Plates ©2005 Robert J. Lillie Plate Boundaries Introduction to Geophysics-KFUPM
7. 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. 8. Introduction to Geophysics-KFUPM Due to shallow hot mantle Due to cold lithospheric plate Map of P-wave Velocity (km/s)
9. 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. 10. Introduction to Geophysics-KFUPM Map of P-wave Velocity (km/s)
11. 11. Introduction to Geophysics-KFUPM Crustal thinning due to Continental rifting Remember that Red Sea is a good example for Continental Rifting. Map of Crustal Thickness (km)
12. 12. Parks and Plates ©2005 Robert J. Lillie Crustal Thinning at Continental Rifts Introduction to Geophysics-KFUPM As the lithosphere rips apart, the underlying asthenosphere becomes shallow while the crust still fairly thick. The buoyancy of the shallow asthenosphere and thick crust results in high overall elevation of the Basin.
13. 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. 14. Crustal Thinning at Continental Rifts Parks and Plates ©2005 Robert J. Lillie Introduction to Geophysics-KFUPM As the continental crust thins, it is less buoyant. Elevations are lower through the region.
15. 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. 16. Parks and Plates ©2005 Robert J. Lillie Crustal Thinning at Continental Rifts Introduction to Geophysics-KFUPM
17. 17. Parks and Plates ©2005 Robert J. Lillie Salton Sea Gulf of California Crustal Thinning at Continental Rifts Introduction to Geophysics-KFUPM
18. 18. Continental Rifting eventually open an Ocean Basin Parks and Plates ©2005 Robert J. Lillie Introduction to Geophysics-KFUPM Red Sea is a good example for Continental Rifting (see pp. 50, Lillie 2005).
19. 19. Parks and Plates ©2005 Robert J. Lillie Continental Rifting eventually open an Ocean Basin Introduction to Geophysics-KFUPM
20. 20. Parks and Plates ©2005 Robert J. Lillie Continental Rifting eventually open an Ocean Basin Introduction to Geophysics-KFUPM
21. 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. 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. 23. Parks and Plates ©2005 Robert J. Lillie Active Continental Rifts Death Valley Salton Sea Introduction to Geophysics-KFUPM National Park Lands
24. 24. Moho DEPTH relate to tectonic history? Introduction to Geophysics-KFUPM Fig.4.17 of Lillie
25. 25. Introduction to Geophysics-KFUPM Fig 4.18 of Lillie
26. 26. Formation of Oceanic Crust Introduction to Geophysics-KFUPM Parks and Plates ©2005 Robert J. Lillie
27. 27. DIVERGENT PLATE BOUNDARY DEVELOPMENT Introduction to Geophysics-KFUPM Parks and Plates ©2005 Robert J. Lillie
28. 28. Ocean/Continent Subduction Zone Introduction to Geophysics-KFUPM Parks and Plates ©2005 Robert J. Lillie
29. 29. Introduction to Geophysics-KFUPM Fig 4.19 of Lillie
30. 30. Continental Rifting eventually open an Ocean Basin Parks and Plates ©2005 Robert J. Lillie Introduction to Geophysics-KFUPM
31. 31. CONVERGENT PLATE BOUNDARY Subduction Zone Introduction to Geophysics-KFUPM Parks and Plates ©2005 Robert J. Lillie Accretionary Wedge Volcanic Arc
32. 32. CONVERGENT PLATE BOUNDARY Continental Collision Introduction to Geophysics-KFUPM Parks and Plates ©2005 Robert J. Lillie
33. 33. Problems 4-3, 4-5, 4-6, 4-7 Introduction to Geophysics-KFUPM Homework due to April 15