Earthquakes occur when elastic energy is accumulated slowly within the Earth's crust as a result of plate motions and then released suddenly at fractures in the crust called faults. The released energy travels in the form of waves called seismic waves. They always start at the focus. (A focus is where an earthquakes starting place.) The the power would start to travel and hit the epicenter, an epicenter is the point on land directly above the focus, soon on the surface. There are three types of earthquakes, the Primary, Secondary, and surface waves. Primary waves cause the rocks they pass through to change in volume. These waves are the fastest traveling seismic waves and can travel through solids, liquids, and gases. Also called P wave See Note at earthquake. Secondary waves start at the same time as primary waves. Secondary waves travel through Earth's interior at about half the speed of primary waves. Secondary waves are also called S waves. And Surface wave is a mechanical wave that propagates along the interface between differing media. A common example is gravity waves along the surface of liquids, such as ocean waves. Gravity waves can also occur within liquids, at the interface between two fluids with different densities.
Ionic bonding When metals react with non-metals, electrons are transferred from the metal atoms to the non-metal atoms, forming ions . The resulting compound is called an ionic compound .
