Seismic

Seismic geophysical methods are the most commonly used in engineering practice. They are based on elastic wave propagation generated by dynamic input or by seismic events. There are two major geophysical seismic methods, the seismic reflection method and the seismic refraction method.

The seismic reflection method is used to assess underground geological structures by measuring the time required for a seismic wave to return to the surface after being reflected at an interface between subsurface materials with different properties. The propagating waves are, typically, produced via mechanical impact or by explosives and the reflected waves are recorded through specialized sensors placed on the ground’s surface, known as geophones.

The seismic refraction method is similar to the seismic reflection method, the difference being that it measures the arrival time of the refracted seismic waves which propagate along a discontinuity between two subsurface layers with different material properties. This method is applicable when the propagating wave velocity of the subsurface materials increases with depth. Otherwise, it may yield inaccurate results. The utilization of seismic refraction is relatively more cost-efficient and can be applied at a larger area compared to the seismic reflection method.