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 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 year. Smaller magnitude—and consequently less damaging—earthquakes are anticipated with greater frequency on a number of fault systems in California.

In either of these earthquakes, casualties could surpass the previous single greatest loss of life in the United States due to a natural disaster, which was about 6,000 persons killed when a hurricane and storm surge struck the Galveston area of the Texas coast in 1900. The highest loss of life due to earthquakes in the United States occurred in San Francisco in 1906, when 700 people were killed. By way of comparison (in spite of the vast differences in building design and practices and socioeconomic systems) the devastating 1976 Tangshan earthquake in China caused fatalities ranging from the official Chinese Government figure of 242,000 to unofficial estimates as high as 700,000. Fortunately, building practices in the United States preclude such a massive loss of life.

Property losses are expected to be higher than in any past earthquake in the United States. For example, San Francisco in 1906, and Anchorage in 1964, were both much less developed than today when they were hit by earthquakes. And the San Fernando earthquake in 1971, was only a moderate shock that struck on the fringe of a large urban area. Each of these three earthquakes caused damage estimated at about $0.5 billion in the then current dollars. Estimates of property damage for the most probable catastrophic earthquake on the Southern San Andreas (Richter magnitude 8+) and for the less probable but more damaging one (Richter magnitude 7.5) on the Newport-Inglewood fault, are about $15 billion and $70 billion respectively. By comparison, tropical storm Agnes caused the largest economic loss due to a natural disaster in the United States to date but it amounted to only $3.5 billion (in 1972 dollars).

It should be noted, however, that substantial uncertainty exists in casualty and property damage estimates because they are based on experience with only moderate earthquakes in the United States (such as the 1971 San Fernando earthquake) and experience in other countries where buildings are generally less resistant to damage. The uncertainty is so large that the estimated impacts could be off by a factor of two or three, either too high or too low. Even if these lowest estimates prevail, however, the assessment about preparedness and the capability to respond to the disasters discussed in this report would be substantially unchanged.

Assuming a catastrophic earthquake, a variety of secondary problems could also be expected. Search and rescue operations—requiring heavy equipment to move debris—would be needed to free people trapped in collapsed buildings. It is likely that injuries, particularly those immediately after the event, could overwhelm medical capabilities, necessitating a system of allocating medical resources to those who could be helped the most. Numerous local fires must be expected; nevertheless, a conflagration such as that which followed the Tokyo earthquake of 1923,