Introduction to Geophysics

Ali Onceloncel@kfupm.edu.

saDepartment of Earth SciencesKFUPM

Seismic Reflection 2: Acquisiton, Processing, and Waveform Analysis

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Previous Lecture

What Seismic Reflection Provides? What requires for a successful study of Reflection? What provides Seismic Reflection on subsurface geological Model? On Land- Seismic Reflection On Sea- Seismic Reflection: Photos from Seismic Crew Equipments: Vibrator Track and Receiver Truck, Geophones, Battery What is a seismic section? what is a Seismic Line? Nature of Seismic Section? Acoustic Impedance Enhancement the quality for Compressional waves? Single Channel Seismic Reflection? What is a seismic Profile?

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Reflection SeismologyIn

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Seismic MethodsIn

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Snell’s Law

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Reflection “Presentation”

Refraction (first arrival)

Reflection 1

Reflection 2

Reflection 3 (dipping)

Reflected refractions

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Angle Incidence = Angle Reflection

Multifold Reflections

Four fold coverage of the CMP

Receiver ArraysIn

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Common Depth Point

Common Midpoint

Many Source Receiver Offsets

Sample Same Depth Point

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CMP Method

Figure 6.4 of Reynolds

Sixfold coverage

of the CDP

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CMP

Method

Sample Same Subsurface Point – Common Depth Point 4 Times

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Processing

Fold of Stack

Coverage

Redundancy

Improve Signal to Noise Ratio

21

220 V

XtT f

fT=Travel time from source, to interface, to receiver

X= horizontal distance from source to receiverV1= seismic velocity of layer above distance

T0= T-axis intercept (time directly down to interface,

straight back up to shot location

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h = thickness of layer above interfaceV1= seismic layer of above interface

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TNMO= Tf - t0

Normal moveout is the difference between the travel time and hyperbola (Tf) and the intercept time (t0).

Normal Moveout

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XTNMO

See EQ 4-10 of Robinson and Coruh, 1988