Refraction seismics

In refraction seismics, we determine the seismic velocity of the subsurface by measuring the dip of wave arrivals. To carry out such a survey, we first set up geophones along a line. Then we create seismic waves at several shot locations (e.g., by striking the ground with a hammer or using explosives).

For each shot location, we determine subsurface velocities using the approach explained in section Travel times. We can then combine the information to determine subsurface variation along a profile. This can be done using an inversion approach, where the input data are the arrival times of the refracted waves, and the output is a subsurface velocity image.

Contents:

• Travel times
• Interpretation when layers are dipping
• Irregular Surfaces and the Plus-Minus Method
• Interpretation Pitfalls and Strategies