Tectonic Interpretation of Seismic Refraction Profiles

Introduction to Geophysics

Ali Onceloncel@kfupm.edu.

saDepartment of Earth SciencesKFUPM

Tectonic Interpretation of Seismic Refraction Tectonic Interpretation of Seismic Refraction ProfilesProfiles

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

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

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

In order for the refracted ray to be the first arrival, the line must be longer than the critical distance.

Plate BoundariesIn

Raised Relief Map of North America and Adjacent Oceans

Due to shallow

hot mantle

Due to cold lithospheric

Map of P-wave Velocity (km/s)

Active Continental

RiftsAdvanced Rifting

(Lower Elevations)

Early Rifting (Higher

Elevations)

National Park

Map of P-wave Velocity (km/s)

Continental rifting

Thin crust.

Map of Crustal Thickness (km)

Crustal Thinning at Continental Rifts

Grand Teton National Park, WyomingGreat Basin National Park, Nevada

Sagauro National Park, ArizonaDeath Valley National Park, California

Salton SeaGulf of California

Continental Rifting eventually open an Ocean Basin

Parks and Plates

East Pacific Rise

Mid-Atlantic Ridge

A Continental Rift can be Viewed as the On-land Continuation of a Mid-Ocean Ridge

Parks and Plates

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

Parks and Plates

Active Continental

Death Valley

Salton Sea

National Park

Moho DEPTH relate to tectonic history?

Fig.4.17 of Lillie

Fig 4.18 of Lillie

Formation of Oceanic Crust

DIVERGENT PLATE BOUNDARYDEVELOPMENT

Ocean/Continent Subduction ZoneIn

Fig 4.19 of Lillie

CONVERGENT PLATE BOUNDARY

Subduction Zone

AccretionaryWedge Volcanic

CONVERGENT PLATE BOUNDARY

Continental Collision

Problems

4-3, 4-5, 4-6, 4-7

Homework due to Next Wednesday

Tectonic Interpretation of Seismic Refraction Profiles

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