What Causes an Earthquake? Faults Explained We all have our faults, and that includes planet Earth. Earthquakes rattle the globe every day, big and small, most recently making news this week with temblors in Puerto Rico and southern California. They all spring from faults deep underground, but what kind? The impact and severity of each quake depends on the answer to that question. (See video: "Earthquakes 101.") The Earth's crust is made of a jigsaw puzzle of continental and oceanic plates that are constantly ramming each other, sliding past each other, or pulling apart. Why Do Earthquakes Happen? Earthquakes are usually caused when rock underground suddenly breaks along a fault. This sudden release of energy causes the seismic waves that make the ground shake. When two blocks of rock or two plates are rubbing against each other, they stick a little. They don't just slide smoothly; the rocks catch on each other. The rocks are still pushing against each other, but not moving. After a while, the rocks break because of all the pressure that's built up.
Ring of Fire The Ring of Fire is a string of volcanoes and sites of seismic activity, or earthquakes, around the edges of the Pacific Ocean. The Ring of Fire isnt quite a circular ring. Its shaped more like a 40,000-kilometer (25,000-mile) horseshoe. Fault Heals Surprisingly Fast After Wenchuan Earthquake For the first time, scientists have watched the Earth heal itself after an earthquake. The process is similar to the body repairing a cut, researchers from China and the United States report today (June 27) in the journal Science. During an earthquake, the ground tears apart along a fault, leaving a jagged series of fractures. After China's devastating magnitude 7.9 Wenchuan earthquake in 2008, fluids filled the fractured fault, like blood gushing into a wound, the team found by drilling into the fault. Within two years — a blink of the eye in geologic time — the fault was speedily knitting itself back together, closing gaps through a combination of processes.
rift valley A rift valley forms where the Earth’s crust, or outermost layer, is spreading or splitting apart. This kind of valley is often narrow, with steep sides and a flat floor. Rift valleys are also called grabens, which means “ditch” in German. While there is no official distinction between a graben and a rift valley, a graben usually describes a small rift valley. Rift valleys differ from river valleys and glacial valleys because they are created by tectonic activity and not by the process of erosion. Rift valleys are created by plate tectonics.
Geography in the News: New Madrid Earthquake Earthquake dangers from the New Madrid fault. With the recent earthquakes in Haiti, New Zealand and Japan, Americans may wonder if or when such a disaster will or might happen closer to home. While most Americans know of the potential for earthquakes along the West Coast’s San Andreas Fault, fewer realize that a major fault line lies near Memphis, Tenn. The New Madrid (MAH dred) fault is one of the most dangerous in the world. Undersea Geology 1. Brainstorm and define underwater landforms. Explain to students that they will be exploring Earth's ocean floor and the types of geologic activity that occur there. Have students imagine what the ocean floor might be like.
Next Great Quake: Drilling the San Andreas Fault for Answers April 17, 2006 In dusty California hills geologists have drilled miles into the Earth to monitor earthquakes where they begin. It's all part of an effort to better prepare the state for the type of megaquake that struck San Francisco a hundred years ago tomorrow. The scientists are using techniques borrowed from the petroleum industry, but they're not searching for oil. Rather, they're hoping to learn the secrets of the San Andreas Fault's "earthquake machine." The project is called SAFOD—short for the San Andreas Fault Observatory at Depth.
Southern California Long Overdue for Quake, Experts Say August 13, 2007 It's only a matter of time before a massive earthquake shakes Southern California to its core, scientists say. Though dormant for more than 300 years, the southern end of the San Andreas Fault is long overdue for a giant upheaval, according to experts. And the results of such a quake would be devastating.