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.