Seismic testing uses seismic waves, created by ‘thumping’ the ground with heavy weights, to read
the subsurface. The waves travel through the ground, hit different layers of rock, fractured zones, and
other variations in density beneath the surface of the Earth, and return to the surface at different times. The
waves are recorded and analyzed to create an image of the rock layers beneath the surface. These tests
are usually run along roads or other straight paths, and interpreted with other seismic tests to search for existing fractures and other structures in the subsurface that could potentially interact with a hydraulic fracturing
treatment. Because seismic testing can be done from Earth’s surface, it is sometimes used after hydraulic fracturing to explore the accuracy of the model of fracturing in predicting actual fracture patterns.