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.