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

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 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