Seismic refraction across the La Bajada Fault

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Seismic refraction across the La Bajada Fault

• Yusliza Mohd Sufian
• UNIVERSITY OF TEXAS AT AUSTIN
• SAGE 2004

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Outline

• Objectives
• Data processing
• Results
• Conclusions

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Objective

• To find layers deeper than the basalt layer
  (below 80 m depth) using the wide angle
  reflection method

Why? High velocity basalt flows limits imaging
underlying layers or structures using near
vertical incidence reflection
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SAGE 2004 Seismic Line
101
457
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Data Processing

• Deconvolution
• Wide angle reflection method
• T2 vs. X2 method

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Deconvolution

• to eliminate reverberation and some of surface
  waves
• Example

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Wide angle reflection

• Definition
• reflection where the angle of incidence is near
  or greater than the critical angle
• Concept
• by increasing the offset between source and
  receiver, the energy reflected on a seismic
  interface increases as compared to the energy
  transmitted through the interface

Relative energy
Angle of incidence
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(No Transcript)
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ID wide angle reflection

• Faster than head waves
• Example 1

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• Example 2

Offset (m)
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T2 vs X2

• Calculate 1-D velocity model
• Parameters
• time, t (s) and offset, x (m)

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Results
1-D velocity model at shotpoint 101
Data points for each layer at shotpoint 101
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Data points for each layer at shotpoint 457
1-D velocity model at shotpoint 457
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Stratigraphy of the 1-D velocity model
Alluvium
Basalt rubble
Santa Fe Group
Santa Fe Group
1-D velocity model at 101
1-D velocity model at 457
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Conclusions

• Wide angle reflection method helps to identify
  layers beneath the basalt layer
• Layer with velocity more than 3 km/s at depth 400
  to 500 m depth
• No basalt layer in the velocity model because it
  is a thin layer