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 more destructive because of its
relative proximity to the most heavily developed regions; however, the
probability of this event is estimated to be only about 0.1 percent per