Reflection and refraction of seismic waves
Topic: Interior of the Earth: Earthquakes, Volcanoes and the Layered Earth · NCERT: Class 11, Ch 3 "Interior of the Earth"
Meaning
Seismic waves change speed as they pass through different materials. In general, the denser the material, the faster they travel. Where one kind of material meets another, waves either bounce back, which is reflection, or bend and change direction, which is refraction. By timing when these bounced and bent waves reach seismographs, scientists can find the boundaries between the earth's layers. Each such boundary is called a discontinuity.
Example
In 1909, Andrija Mohorovicic of Croatia noticed that seismic waves suddenly sped up at a certain depth. This revealed the boundary between the crust and the mantle, now called the Moho. It lies 5-10 km below the ocean floor and 30-70 km below the continents.
Don't confuse with
- Shadow zone: this is an area on the surface where no direct waves arrive. It is a result of refraction at the core, not the bending itself.