not
suffered any disaster of this magnitude on its own territory since the
Civil War.

The basis for this overall assessment is summarized below and
discussed in more detail in the subsequent chapters of this report.

C. LIKELIHOOD OF FUTURE EARTHQUAKES

Earth scientists unanimously agree on the inevitability of major
earthquakes in California. The gradual movement of the Pacific Plate
relative to the North American Plate leads to the inexorable
concentration of strain along the San Andreas and related fault
systems. While some of this strain is released by moderate and smaller
earthquakes and by slippage without earthquakes, geologic studies
indicate that the vast bulk of the strain is released through the
occurrence of major earthquakes--that is, earthquakes with Richter
magnitudes of 7.0 and larger and capable of widespread damage in a
developed region. Along the Southern San Andreas fault, some 30 miles
from Los Angeles, for example, geologists can demonstrate that at
least eight major earthquakes have occurred in the past 1,200 years
with an average spacing in time of 140 years, plus or minus 30 years.
The last such event occurred in 1857. Based on these statistics and
other geophysical observations, geologists estimate that the
probability for the recurrence of a similar earthquake is currently as
large as 2 to 5 percent per year and greater than 50 percent in the
next 30 years. Geologic evidence also indicates other faults capable
of generating major earthquakes in other locations near urban centers
in California, including San Francisco-Oakland, the immediate Los
Angeles region, and San Diego. Seven potential events have been
postulated for purposes of this review and are discussed in chapter
II. The current estimated probability for a major earthquake in these
other locations is smaller, but significant. The aggregate probability
for a catastrophic earthquake in the whole of California in the next
three decades is well in excess of 50 percent.

D. CASUALTIES AND PROPERTY DAMAGE

Casualties and property damage estimates for four of the most likely
catastrophic earthquakes in California were prepared to form a basis
for emergency preparedness and response. Chapter III gives details on
these estimates. Deaths and injuries would occur principally because
of the failure of man-made structures, particularly older, multistory,
and unreinforced brick masonry buildings built before the adoption of
earthquake