Final answer:
A seismic survey is used to determine the shape and position of underground boundaries by sending sound waves into the Earth and analyzing their reflections.
Step-by-step explanation:
A seismic survey is used to determine the shape and position of boundaries. This method is vital in geology and involves sending sound waves into the ground or ocean. As these waves interact with different layers of rock or sediment, some waves are reflected back and recorded by geophones, providing an image of the subsurface. This technique helps geologists and other Earth scientists understand the structure beneath the surface, which is crucial for identifying plate boundaries and assessing geological hazards.