Following are brief descriptions of postulated events. Figure 1 gives their geographic location.
1. Los Angeles-San Bernardino/Southern San Andreas Fault (Magnitude 8.3)
For the past several thousand years, great earthquakes have been occurring over a 300 km length of the San Andreas fault approximately every 100 to 200 years, 140 years on the average. The last such event took place in 1857. The probability of occurrence of this earthquake is estimated to be currently as large as 2 to 5 percent per year and greater than 50 percent in the next 30 years. The fault skirts the edge of the Los Angeles-San Bernardino metropolitan region, thus most of the urbanized area lies further than 20 miles from the source of strong shaking. Because of the distance, shaking would be more hazardous for large structures than for one- to two-story houses. The long duration of shaking could trigger numerous slides on steep slopes and cause liquefaction in isolated areas.
2. San Francisco Bay Area/Northern San Andreas Fault (Magnitude 8.3)
A repeat occurrence of the 1906 earthquake, in which the San Andreas fault broke over 400 km of its length, would cause severe damage to structures throughout the Bay Area and adjacent regions. The extensive urban development on lowlands and landfill around San Francisco Bay would be especially hard hit and liquefaction in many of these areas would intensify the damage to structures erected on them.
3. San Francisco Bay Area/Hayward Fault (Magnitude 7.4)
The last large events to occur on this fault were in 1836 and 1868. Should a major earthquake occur, severe ground shaking and liquefaction is expected to cause damage throughout the entire circum-bay area nearly as severe as that resulting from a 1906-type earthquake on the San Andreas fault. This earthquake would be of particular concern because of the many dams located along or near the fault.
4. Los Angeles/Newport-Inglewood Fault (Magnitude 7.5)
This earthquake would be a serious threat to the nearby, densely-populated areas of Los Angeles. Shaking would cause extensive structural damage throughout the Los Angeles Basin and liquefaction near the coast would add still more destruction.
5. San Diego Area/Rose Canyon Fault (Magnitude 7.0)