Most earthquakes are produced by the rapid release of elastic energy stored in rock that has been subjected to great forces. When the strength of the rock is ___________ , it suddenly breaks, causing the __________ of an earthquake .
Scientists have used two different measurements to describe the size of an earthquake – intensity and magnitude .
_________ is the amount of shaking at a given location based on earthquake damage.
_____________ are quantitative measurements that rely on calculations using seismographs. Magnitudes are a measure of the size of seismic waves or the amount of energy released at the source of the earthquake.
This is the scene of the most violent earthquake in North America during the 20 th century. The moment magnitude was 9.2 and the event lasted 3-4 minutes. The quake left 131 dead and thousands homeless. The state’s economy was badly damaged. However, if this quake had happened on an average weekday, many more lives would have been lost.
__________ – 1906, San Francisco…..many wood structures burned when gas and electric lines where cut. Many water lines were broken crippling firefighters. In 1923, an earthquake in Japan caused an estimated 250 fires. These fires destroyed half of Tokyo and killed over 100,000 people.
__________ – crust (both oceanic and continental) and the uppermost mantle.
__________ – under the lithosphere, it is slightly weaker than the crust. Its temperature and pressure results in a small amount of melting. Rocks here are close enough to their melting point and therefore __________.
Another boundary was found between the mantle and the outer core. P waves are bent around the outer core. The outer core causes P waves that travel through the core to arrive several minutes later than expected. This region is called the __________.