What is the Source of the Earthquake Earthquake is another destructive natural phenomenon. To be able to understand what an earthquake is, we need to understand the internal structure of the Earth.Crust is the thin outer covering of the Earth. The crust is thinner at the ocean floor (about 6-11 km) than under the continents (about 30-70 km). Outer core is about … [Read more...] about What is the Source of the Earthquake