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Introduction to Geophysics
Ali [email protected].
saDepartment of Earth SciencesKFUPM
Tectonic Interpretation of Seismic Refraction Tectonic Interpretation of Seismic Refraction ProfilesProfiles
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Previous Lecture
•Hidden Layers •Problem Situations • Low Velocity layer (V2<V1<V3) •Thin layer (V3>V2>V1 but h2 very small) •Velocity Inversion-Hidden Layers
•Dipping Layer Refractions•Single Dipping Refractor Surface
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1.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 1In
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1.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 2In
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Solutions of Quiz 2: Question 2In
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ic
In order for the refracted ray to be the first arrival, the line must be longer than the critical distance.
Parks and Plates©2005 Robert J. Lillie
Plate BoundariesIn
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A. J
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Parks and Plates©2005 Robert J. Lillie
Raised Relief Map of North America and Adjacent Oceans
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Due to shallow
hot mantle
Due to cold lithospheric
plate
Map of P-wave Velocity (km/s)
Parks and Plates©2005 Robert J. Lillie
Active Continental
RiftsAdvanced Rifting
(Lower Elevations)
Early Rifting (Higher
Elevations)
National Park
Lands
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Map of P-wave Velocity (km/s)
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Continental rifting
Thin crust.
Map of Crustal Thickness (km)
Parks and Plates©2005 Robert J. Lillie
Crustal Thinning at Continental Rifts
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Crustal Thinning at Continental Rifts
Parks and Plates©2005 Robert J. Lillie
Grand Teton National Park, WyomingGreat Basin National Park, Nevada
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Crustal Thinning at Continental Rifts
Parks and Plates©2005 Robert J. Lillie
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Parks and Plates©2005 Robert J. Lillie
Sagauro National Park, ArizonaDeath Valley National Park, California
Crustal Thinning at Continental Rifts
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Parks and Plates©2005 Robert J. Lillie
Crustal Thinning at Continental Rifts
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Parks and Plates©2005 Robert J. Lillie
Salton SeaGulf of California
Crustal Thinning at Continental Rifts
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Continental Rifting eventually open an Ocean Basin
Parks and Plates©2005 Robert J. LillieIn
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Parks and Plates©2005 Robert J. Lillie
Continental Rifting eventually open an Ocean Basin
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Parks and Plates©2005 Robert J. Lillie
Continental Rifting eventually open an Ocean Basin
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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
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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
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Parks and Plates
©2005 Robert J. Lillie
Active Continental
Rifts
Death Valley
Salton Sea
National Park
Lands
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Moho DEPTH relate to tectonic history?
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Fig.4.17 of Lillie
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Fig 4.18 of Lillie
Formation of Oceanic Crust
Parks and Plates©2005 Robert J. Lillie
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Parks and Plates©2005 Robert J. Lillie
DIVERGENT PLATE BOUNDARYDEVELOPMENT
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Parks and Plates©2005 Robert J. Lillie
Ocean/Continent Subduction ZoneIn
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Fig 4.19 of Lillie
Continental Rifting eventually open an Ocean Basin
Parks and Plates©2005 Robert J. Lillie
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CONVERGENT PLATE BOUNDARY
Subduction Zone
Parks and Plates©2005 Robert J. Lillie
AccretionaryWedge Volcanic
Arc
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CONVERGENT PLATE BOUNDARY
Parks and Plates©2005 Robert J. Lillie
Continental Collision
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Problems
4-3, 4-5, 4-6, 4-7
Homework due to Next Wednesday
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