National severe weather Step into the wild world of weather! What is a wall cloud? What's the difference between a watch and a warning? Is it ever “too cold to snow”? Learn all about thunderstorms, tornadoes, hail, lightning, floods, damaging winds and severe winter weather. Earthquake Facts The origin of the name of the San Andreas Fault is often cited as the San Andreas Lake. However, based on some 1895 and 1908 reports by geologist A.C. Lawson, who named the fault, the name was actually taken from the San Andreas Valley. He likely did not realize at the time that the fault ran almost the entire length of California!
Animations for Earthquake Terms and Concepts AmplificationShaking levels at a site may be increased, or amplified, by focusing of seismic energy caused by the geometry of the sediment velocity structure, such as basin subsurface topography, or by surface topography. AsperityAn asperity is an area on a fault that is stuck. The earthquake rupture usually begins at an asperity. AttenuationWhen you throw a pebble in a pond, it makes waves on the surface that move out from the place where the pebble entered the water. The waves are largest where they are formed and gradually get smaller as they move away. This decrease in size, or amplitude, of the waves is called attenuation.
BUILDING BIG: Home Page Explore large structures and what it takes to build them with BUILDING BIG™, a five-part PBS television series and Web site from WGBH Boston. Here are the main features of the site: Bridges, Domes, Skyscrapers, Dams, and Tunnels. Earthquake Facts, Earthquake Information, Earthquake Videos, Earthquake Photos Earthquakes, also called temblors, can be so tremendously destructive, it’s hard to imagine they occur by the thousands every day around the world, usually in the form of small tremors. Some 80 percent of all the planet's earthquakes occur along the rim of the Pacific Ocean, called the "Ring of Fire" because of the preponderance of volcanic activity there as well. Most earthquakes occur at fault zones, where tectonic plates—giant rock slabs that make up the Earth's upper layer—collide or slide against each other.
Faultline: Theory of Plate Tectonics The answer is that some places on the earth's surface are, literally, on the edge. During its early years, the earth's outer layer was much hotter than it is today. Over time, the surface of the earth cooled and hardened. Virtual Earthquake - An Introduction What's an earthquake? Earthquakes occur because of a sudden release of stored energy. This energy has built up over long periods of time as a result of tectonic forces within the earth. Most earthquakes take place along faults in the upper 25 miles of the earth's surface when one side rapidly moves relative to the other side of the fault. This sudden motion causes shock waves (seismic waves) to radiate from their point of origin called the focus and travel through the earth. It is these seismic waves that can produce ground motion which people call an earthquake.
Lawrence Hall of Science - 24/7 Science How fast does the wind blow? What makes things sticky? Where do insects live and plants grow? Earthquake facts An earthquake is caused by a sudden slip on a fault. A fault is a fracture in the crust of the earth along which rocks on one side have moved relative to those on the other side. Stresses in the earth’s outer layer push the sides of the fault together, pressure builds up and the rocks slip suddenly, releasing energy in waves that travel through the rock to cause the shaking that we feel during an earthquake. Earthquakes tend to be concentrated in narrow zones. There are 7 major crustal plates on earth, about 50 miles (80 km) thick, all in constant motion relative to one another, moving at the speed at which your fingernail grows, at between 10 and 130 mm (from less than one half to 5 inches) per year. It is estimated that there are several million earthquakes in the world each year.