1. Seismic refraction along a profile across the La Bajada fault Max Moorkamp

2. Outline Seismic refraction method Area of study and objectives Data Models and interpretation Conclusions

3. Seismic 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

4. Slope 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

5. Slope intersect method

6. Area 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

7. Data for Site 457

8. Slope-Intercept Models Sites 101 – 281Sites 161 - 341 Sites 221 - 401 Sites 281 – 457

9. Combined Models Loose Dirt Basalt Sites 457 - 221 Sites 101 - 161 Santa Fe Form. Basaltic rubble Quart. Sed.

10. Conclusions 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