SWSE- Earthquake Facts and Historical Data

Printable Version Today in earthquake history A list of the most destructive known earthquakes. Tables displaying the relation between magnitude and energy. Various historical and scientific data: 1. The earliest reported earthquake in the current geographical region of California occurred in 1769 and was reported by Gaspar de Portola while on an expedition southeast of Los Angeles. The first reported earthquake in the current geographical region of America occurred in 1663.

2. The San Andreas fault system experiences a relative motion of approximately 56 mm per year, at which rate Los Angeles and San Francisco would meet in some fifteen million years. It is not one fault, but a system of faults over eight hundred miles in length occurring between the Pacific Plate and the North American Plate. The San Andreas is a right-lateral, strike-slip fault, meaning that the plates move horizontally to one another. The Pacific Plates moves north as compared to the North American Plate.

3. Southern California has a reputation as an area of notable seismic activity. Each year, approximately ten thousand earthquakes are recorded in the region each year, of which fifteen to twenty are of magnitude 4.0 or greater. These earthquakes constitute two percent of the world's annual quakes. 4. Seismic activity is recorded according to magnitude, a measurement of the size of earthquake, and according to the intensity, which is dependant upon the location of the observer. Various scales have been used, the most recent of which is based a calculated seismic moment, which has the units MW. 5. Human recordings of earthquakes date back to the second millennium BC, but it was not until 1760 AD that their cause was correctly identified, by British engineer John Mitchell.

6. The largest recorded earthquake in the world was a magnitude 9.5 MW earthquake in Chile on May 22, 1960. The largest in US history since 1900 was a 9.2 MW quake in Alaska on March 28, 1964.	Alaska, 1964. Fault scarp with maximum vertical displacement of fourteen feet. Click to enlarge.