Seismic refraction along a profile across the La Bajada fault
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Transcript of Seismic refraction along a profile across the La Bajada fault
Seismic refraction along a Seismic refraction along a profile across the La Bajada profile across the La Bajada
faultfaultMax MoorkampMax Moorkamp
OutlineOutline
• Seismic refraction method
• Area of study and objectives
• Data
• Models and interpretation
• Conclusions
Seismic refraction methodSeismic refraction method
• Uses refractions from interfaces to determine seismic velocities
• At long distances the first arrival travels through deep layers
• The Slope-Intersect-Method can be used to determine layer velocities and thickness
• Results can be checked by calculating theoretical travel times from models
Slope intersect methodSlope intersect method
• Determine slope and intersect of first arrivals
• Each slope and intersect corresponds to one layer
• Information from 2 different sites can be used to obtain dip of layers
Slope intersect methodSlope intersect method
Area of study and objectivesArea of study and objectives
• Obtain velocity structure in the sub-surface
• Determine position of the La Bajada fault
• Estimate fault offset from position of basalt layer
Suspected fault position
Data for Site 457Data for Site 457
Slope-Intercept ModelsSlope-Intercept Models
Sites 101 – 281Sites 161 - 341
Sites 221 - 401Sites 281 – 457
Combined ModelsCombined Models
Loose Dirt
Basalt
Sites 457 - 221 Sites 101 - 161
Santa Fe Form.
Basaltic rubble
Quart. Sed.
ConclusionsConclusions
• The La Bajada fault is probably located between seismic sites 161 and 221
• The top of the basalt is only present to the west at a depth of 80 m
• The displacement on the fault is 200 m in 4My