An Assessment of the Consequences and Preparations for a Catastrophic California Earthquake: Findin | Page 2

using these
institutions to foster hazard reduction
» An examination of the appropriate role of insurance in mitigating the
impacts of earthquakes.
More recently, a cooperative Federal, State, local, and private-sector
effort was initiated to prepare for responding to a credible
large-magnitude earthquake, or its prediction, in Southern California.
B. SUMMARY
The review provided the overall assessment that the Nation is
essentially unprepared for the catastrophic earthquake (with a
probability greater than 50 percent) that must be expected in California
in the next three decades. While current response plans and
preparedness measures may be adequate for moderate earthquakes,
Federal, State, and local officials agree that preparations are woefully
inadequate to cope with the damage and casualties from a catastrophic
earthquake, and with the disruptions in communications, social fabric,
and governmental structure that may follow. Because of the large
concentration of population and industry, the impacts of such an
earthquake would surpass those of any natural disaster thus far
experienced by the Nation. Indeed, the United States has 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-resistant building codes. Experience has shown that some
modern multistory buildings--constructed as recently as the late 1960's
but not adequately designed or erected to meet the current
understanding of requirements for seismic resistance--are also subject

to failure. Strong ground shaking, which is the primary cause of
damage during earthquakes, often extends over vast areas. For example,
in an earthquake similar to that which occurred in 1857, strong ground
shaking (above the threshold for causing damage) would extend in a
broad strip along the Southern San Andreas fault, about 250 miles long
and 100 miles wide, and include almost all of the Los Angeles-San
Bernardino metropolitan area, and all of Ventura, Santa Barbara, San
Luis Obispo, and Kern counties.
For the most probable catastrophic earthquake--a Richter magnitude 8+
earthquake similar to that of 1857, which occurred along the Southern
San Andreas fault--estimates of fatalities range from about 3,000, if the
earthquake were to occur at 2:30 a.m. when the population is relatively
safe at home, to more than 13,000, if the earthquake were to occur at
4:30 p.m. on a weekday, when much of the population is either in
office buildings or on the streets. Injuries serious enough to require
hospitalization under normal circumstances are estimated to be about
four times as great as fatalities. For the less likely prospect of a Richter
magnitude 7.5 earthquake on the Newport-Inglewood fault in the
immediate Los Angeles area, fatalities are estimated to be about 4,000
to 23,000, at the same respective times. Such an earthquake, despite its
smaller magnitude, would be