tectonic interpretation of seismic refraction profiles 2

$: Tectonic Interpretation of Seismic Refraction Profiles 2$
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

•Quiz

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ΔX=10 m

Can you pick out the direct arrival?

• A= Direct Arrival, tA1=0.003 sec, tA2 …………

• Can you pick out the refraction arrivals? How much critical refraction is there? 2 Critical Refractions: B and C

• tB1=0.01msec , tc1=0.016 sec• How would you determine the refraction velocity?• V2= 45m/0.007 sec =6750m/sec• V3= 148m/0.001 =14800 m/secHow would you determine the air wave or direct arrival

velocity?• Vdirect= 33m/0.01 sec =3300 m/sec• Vair= 33m/0.034 sec =963 m/sec

0.00

7

0.01

148 m

45 m0.01

0.02

0.03

0.04

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0.01

Sec

ond

0.03

4

A= Direct Wave

B= First Ref raction

C= Second Ref raction

Problem 3.2 in pp. 127 Berger's book.

Figure is a field seismograph from a region with horizontal interfaces. Interpret the data.

First geophone is at 3 meters from the source, the remainder are spaced at 10m intervals.

•What can you see?

•How many layers indicated by the shot record?

•What are their velocities?

•What are the time intercepts?

•Determine the thickness of each layer?

Homework due to April 15

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P.C: 1 milisecond is 10^-3 seconds

First geophone is at 3 meters from the source, the remainder are spaced at 10m intervals.

What can you see?

•How many layers indicated by the shot record?

•What are their velocities?

•What are the time intercepts?

•Determine the thickness of each layer?

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.


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P.C: 1 milisecond is 10^-3 seconds

Parks and Plates©2005 Robert J. Lillie

Plate BoundariesIn

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A. J

on K

imer

l ing


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)


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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Crustal thinning due to Continental rifting

Remember that Red Sea is a good example for Continental Rifting.

Map of Crustal Thickness (km)


Crustal Thinning at Continental Rifts

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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.



Grand Teton National Park, WyomingGreat Basin National Park, Nevada

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As the continental crust thins, it is less buoyant. Elevations are lower through the region.


Sagauro National Park, ArizonaDeath Valley National Park, California


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Salton SeaGulf of California


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Continental Rifting eventually open an Ocean Basin

Parks and Plates©2005 Robert J. LillieIn

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Red Sea is a good example for Continental Rifting

(see pp. 50, Lillie 2005).



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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


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


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


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DIVERGENT PLATE BOUNDARYDEVELOPMENT

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Ocean/Continent Subduction ZoneIn

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Fig 4.19 of Lillie



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CONVERGENT PLATE BOUNDARY

Subduction Zone


AccretionaryWedge Volcanic

Arc

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CONVERGENT PLATE BOUNDARY


Continental Collision

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Problems

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

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tectonic interpretation of seismic refraction profiles 2

Technology

lillie introduction

geophysicskfupm p

geophysicskfupm fig

continental rifts introduction

geophysicskfupm map

geophysicskfupm red

nevada introduction

continental rifts parks