Even it you’ve never felt an earthquake, you’ll know they can be devastating. Films like 2012 feature ‘mega quakes’, where gaping fissures swallow people and buildings. Real-life earthquakes are less dramatic than those in the movies, but they’re still one of nature’s worst natural hazards. Unstoppable and terrifying, big quakes strike with little or no warning, flattening cities and killing tens of thousands of people. Most of the world’s earthquakes occur at the boundaries between the Earths huge crustal plates. These boundaries are called faults, and the plates – of which there are 15 of varying different sizes here on Earth – jostle on the planet’s surface like the pieces of a giant, floating jigsaw puzzle. in some parts of t he world, these crustal plates grate past each other. In other places, they collide or are pull. apart. Faults break open as these rigid plates move and exert forces great enough to crush and tear solid rock. As the plates move about, the rock slabs at either side of faults are dragged past each other. But rocks are jagged and uneven, meaning there, lots of friction between them. This friction causes the rocks to become lock. together. Pressure builds along the fault as the plates grind along, squeezing and st retching t he rocks until, eventually, they break and lurch forward. Huge amounts of pent-up energy are unleashed, and it, the resulting snap that isan earthquake. The wint at which the Earth’s crust first breaks is call. the earthquake focus. This isusually ma, miles below the Earth, surface. The epicenter is t he point on t he su rface located directly above the focus.
The released energy speeds through the Earth in the form of shock waves. There are three main types of shock wave: primary , secondary and surface waves. Primary waves radiate fastest from the earthquake focus Secondary waves arrive later and surface waves arrive last. The surface waves travel near the Earth,surface, rocking the ground and causing the widespread devastation wrought by the largest earthquakes. People barely feel secondary waves. The size of an earthquake is defined by its magnitude- this is a measure of t he energy releas.. Magn itude isn’t a simple measurement of the relationship between ea nhqua ke size a. energy. Increasing the magnitude by one increases shock wave size by ten times and total energy released by about 30 times.