Earthquakes are the result of plate tectonics, or shifting plates in the crust of Earth, and quakes occur when the frictional stress of gliding plate boundaries builds and causes failure at a fault line. In an earthquake, elastic strain energy is released and waves radiate, shaking the ground. Scientists can predict where major temblors might occur in a general sense, but research does not yet allow forecasts for specific locations or accurate predictions of timing. Major earthquakes, some generating tsunamis, have leveled entire cities and affected whole countries. Relatively minor earthquakes can also be induced, or caused by human activity, including extraction of minerals from Earth and the collapse of large buildings.
The 6.0-magnitude earthquake that rocked California's Napa Valley last month not only injured dozens of people and caused millions of dollars in damage, but it also warped the surface of Earth.
Earthquakes are still rocking Iceland as lava pushes through a long underground fissure near the ice-covered Bardarbunga volcano. New fractures and sinkholes were seen in ice southeast of the volcano today.
A strong, magnitude-6 earthquake in Northern California occurred Sunday on the West Napa Fault. The shaker highlights how both high-tech instruments and old-fashioned groundwork remain important in identifying an earthquake's source.