Part 2 (2/2)

Detailed maps were prepared for each event showing qualitative estimates of ground shaking intensity resulting from each earthquake.

These estimates are indicative of the general severity of damage to ordinary structures. Empirical formulae providing quant.i.tative estimates of peak ground motion at various distances from the postulated earthquakes were developed for use in the effects of severe ground shaking on individual structures or critical facilities. No estimates were made of localized effects, such as ground failures related to liquefaction (the complete failure or loss of strength, of a saturated soil due to shaking), landslides, and fault rupture. These effects can be far more destructive than ground shaking alone.

[Ill.u.s.tration: Figure 1. Geographic Locations of Selected Regional Events]

CHAPTER III

a.s.sESSMENT OF LOSSES FOR SELECTED POTENTIAL CALIFORNIA EARTHQUAKES

A. INTRODUCTION

As part of a program that FEMA and its predecessor agencies have had underway for a number of years, property loss and casualty estimates were prepared in 1972 and 1973 for a number of potential maximum credible earthquakes that could impact on the San Francisco and the Los Angeles areas--North San Andreas (Richter magnitude 8.3), Hayward (Richter magnitude 7.4), South San Andreas (Richter magnitude 8.3), and Newport-Inglewood (Richter magnitude 7.5). These estimates have now been updated as part of the current a.s.sessment.

Estimates of property loss and casualties are based on the expected type and distribution of damage for each postulated earthquake as determined by the size and location of the earthquake and the distribution and character of the buildings and structures within the affected area. Methodologies for estimates of this type are approximate at best. Consequently, the figures shown below may vary upward or downward by as much as a factor of two or three. This degree of uncertainty does not affect the validity of the conclusions of this report, however, since there are greater uncertainties in all other aspects of emergency response planning.

B. PROPERTY LOSS ESTIMATES

The property loss estimates were obtained by first estimating the total replacement dollar value of buildings and their contents, multiplying them by percentage loss factors (inferred from the antic.i.p.ated strength of shaking in each county), and then summing to obtain the aggregate loss. Included in the estimates are private as well as Federal, State, and local government buildings, insured and uninsured. Excluded from consideration is the replacement value of transportation and communication facilities, dams, utility installations, and special purpose structures (e.g., convention centers and sports arenas). Also excluded is the potential damage resulting from a major dam failure or the indirect dollar losses due to such factors as higher unemployment, lower tax revenue, reduced productivity, and stoppage of industrial production. Experience indicates that indirect losses could be approximately equal to the dollar amounts lost in buildings and their contents. The property loss estimates for four postulated earthquakes on the faults listed below are as follows.

TABLE 2

ESTIMATES OF PROPERTY LOSSES FOR REPRESENTATIVE EARTHQUAKES[1]

-------------------------------------------------------------------------- Loss to Loss of Building Contents Total Loss Fault ($ in Billions) ($ in Billions) ($ in Billions) -------------------------------------------------------------------------- Northern San Andreas 25 13 38 Hayward 29 15 44 Newport-Inglewood 45 24 69 Southern San Andreas 11 6 17 ---------- [1] Uncertain by a possible factor of two to three.

C. CASUALTY ESTIMATES

Deaths and injuries in these earthquakes princ.i.p.ally would occur from failures of man-made structures, particularly older, multistory, and unreinforced brick masonry buildings built before the inst.i.tution 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 constructed to meet the current understanding of requirements for seismic resistance--are also subject to failure. Consequently, the number of fatalities will be strongly influenced by the number of persons within high-occupancy buildings, capable of collapsing, or by failure of other critical facilities such as dams. Additional imponderables are the degree of saturation of the ground at the time of the event and the possibility of weather conditions conducive to the spread of fire. A conflagration such as occurred in the 1906 San Francisco earthquake, is not considered likely to occur in any of the a.n.a.lyzed events, however, because of improvements in fire resistance of construction and firefighting techniques. Nonetheless, numerous smaller fires must be antic.i.p.ated in any of the a.n.a.lyzed events and a ”Santa Ana type” wind could cause serious problems.

An additional element of uncertainty in estimating casualties from earthquake stems from not knowing where most of the population will be at the time of the earthquake. In the early morning (i.e., 2:30 a.m.) most people are at home, by far the safest environment during a seismic emergency. At 2:00 in the afternoon, on the other hand, the majority of people are at their places of employment and therefore vulnerable to collapse of office buildings. Around 4:30 p.m. many more people are in the streets and thus subject to injury due to falling debris or failures of transportation systems. Consequently, depending on the time of day, wide variations in the number of casualties can be expected.

Following are estimates of dead and injured (requiring hospitalization) for each of the four representative faults and for the three time periods just discussed.

TABLE 3

ESTIMATES OF CASUALTIES[1]

------------------------------------------------------------------- Fault Time Dead Hospitalized[2]

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