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

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

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

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

Slope intersect method

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

Data for Site 457

Slope-Intercept Models Sites 101 – 281Sites Sites Sites 281 – 457

Combined Models Loose Dirt Basalt Sites Sites Santa Fe Form. Basaltic rubble Quart. Sed.

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