When was the last big earthquake in southern california?

The well-known Richter scale was devised in the 1930s to describe the relative sizes of earthquakes in southern California. In the 1970s, the moment magnitude scale was introduced to describe the physical size of an earthquake, and is preferred for very large earthquakes. read more

The few damaging earthquakes that occurred in the American Midwest and the East Coast were well known (1755 Cape Ann, 1811–12 New Madrid, 1886 Charleston), and it became apparent to settlers that the earthquake hazard situation was much different in the West. read more

Last Tuesday — Sept. 27 — the U.S. Geological Survey issued a statement that the chances of a magnitude 7 or greater earthquake being triggered on the southern San Andreas fault over the next seven days were as high as 1 in 100 and as low as 1 in 3,000. read more