Earthquakes, or seismic tremors, occur at a rate of several hundred per day around the world. A worldwide network of seismographs (machines that record movements of the earth) detects about one million small earthquakes per ye
ar. Very large earthquakes, such as the 1964 Alaskan earthquake, which measured 9.2 on the Richter scale and caused millions of dollars in damage, occur worldwide once every few years. Moderate earthquakes, such as the 1989 tremor in Loma Prieta, California (magnitude 7.0 on the Richter scale), and the 1995 tremor in Kôbe, Japan (magnitude 6.
