How do seismic refraction experiments reveal the layers of oceanic crust?

Seismic refraction experiments are fundamental to understanding the layered structure of the oceanic crust. These experiments involve generating seismic waves via controlled explosions—such as dynamite blasts—set off over distances of several tens of kilometers.1

As these waves travel through the subsurface, they are detected by hydrophones in the water. Because seismic waves travel at different speeds depending on the density and type of rock they encounter, researchers measure the travel times of these waves to determine the crust's internal properties.12

Key aspects of this process include:
* Velocity as a Fingerprint: Seismic velocity increases with depth, acting as a "fingerprint" that allows geologists to correlate specific velocities with known rock types.1
* Time-Distance Analysis: By plotting travel time against the distance between the source and the detector, scientists can calculate the number, thickness, and velocity of distinct rock layers.2
* Layer Identification: Early experiments identified two primary layers beneath the sediment. More sophisticated modern analyses have further refined this, allowing for a detailed model of the crust's composition and layered structure.1