3. EARTHQUAKES 



Earthquake Prediction and Prevention 



The earthquakes that we are really 

 interested in predicting are the largest 

 ones, those capable of taking human 

 life and causing property damage. 

 Earthquakes of this size have occurred 

 countless times in the past few million 

 years, mostly in relatively narrow 

 belts on the earth's surface. 



The destructive powers of earth- 

 quakes and resulting tsunami waves 

 are well known. For example, the ex- 

 tremely destructive Alaskan earth- 

 quake of 1964 killed about 100 people 

 and caused measurable damage to 

 75 percent of Anchorage's total de- 

 veloped worth. The earthquake also 

 generated tsunamis that caused se- 

 vere damage throughout the Gulf of 

 Alaska, along the west coast of North 

 America, and in the Hawaiian Islands. 



A very severe earthquake in 1960 

 killed approximately 2,000 people in 

 Chile and rendered about a half mil- 

 lion people homeless. Property dam- 

 age was estimated to be about $500 

 million. Tsunami damage from this 

 earthquake occurred along the shores 

 of South America, certain parts of 

 North America (principally southern 

 California), the Hawaiian Islands, 

 New Zealand, the Philippines, Japan, 

 and other areas in and around the 

 perimeter of the Pacific Ocean. About 

 $500,000 damage was suffered by the 

 southern California area, while about 

 25 deaths and $75 million damage 

 were suffered by the Hawaiian 

 Islands. The Philippines incurred 

 about 32 deaths. Japan sustained ap- 

 proximately $50 million damage. 



Earthquake Zones — There are two 

 catastrophe-prone zones (see Figure 

 II-5) : first, a region roughly encom- 

 passing the margin of the Pacific 

 Ocean from New Zealand clockwise 

 to Chile, including Taiwan, Japan, 



and the western coasts of Central and 

 South America; and second, a roughly 

 east-west line from the Azores to 

 Indonesia and the Philippines, includ- 

 ing Turkey and Iran and the earth- 

 quake zones of the Mediterranean, 

 especially Sicily and Greece. 



The parts of the United States with 

 a history of severe earthquake inci- 

 dence are the Aleutians, south and 

 southeastern Alaska, and the Pacific 

 coast of continental United States. 

 The two worst earthquakes of the 

 twentieth century in this country 

 were the "Good Friday" quake near 

 Anchorage, noted above, and the San 

 Francisco quake of 1906. In terms 

 of energy release, the 1964 shock may 

 have been two or three times as 

 potent as that of 1906. 



Statistical Generalities — The prob- 

 lem of earthquake prediction is closely 

 related to statistical studies of earth- 

 quake occurrence. Such studies en- 

 able us to make the following gen- 

 eralizations: 



1. Somewhere on the earth there 

 will be a catastrophic earth- 

 quake, one capable of causing 

 death in inhabited areas, on the 

 average of between 2 and 100 

 times a year. Greater precision 

 is not possible, since a strong 

 earthquake in a sparsely popu- 

 lated area will create no major 

 hazard, while the same earth- 

 quake in a densely populated 

 region may or may not cause 

 loss of life, depending on how 

 well the buildings are con- 

 structed. 



2. In any given region in the 

 earthquake-prone zones, a cata- 

 strophic shock will occur on 

 the average of once per so 



many years, depending on the 

 size of the region and how 

 active it is. 



But statistical prediction of this 

 sort is unsatisfactory for an inhabi- 

 tant of a specific region. This person 

 is most concerned with his own region 

 and with a time-scale of much less 

 than 100 years. This person probably 

 needs several months' advance notice 

 of an impending earthquake, although 

 we are nowhere near that goal. 



Even if it were possible to predict 

 an earthquake to the nearest minute 

 or hour, major sociological problems, 

 of the sort associated in the United 

 States with civil defense, would need 

 to be solved. What kind of warning 

 system should there be? How does 

 one handle the dispersal of the crowds 

 involved in possible mass exodus? 

 And what would be the reaction of 

 the public if predictions failed to 

 prove out in, say, 25 percent of the 

 cases? 



Why Earthquakes Occur 



The occurrence of earthquakes in- 

 volves the physics of friction. Accord- 

 ing to the modern theory of rigid-plate 

 tectonics, the earth's surface is cov- 

 ered with a small number of relatively 

 rigid, large plates all in motion rela- 

 tive to one another. At some lines of 

 contact between two plates, the plates 

 are receding from one another and 

 surface area is being created by the 

 efflux of matter from the earth's in- 

 terior. Along other lines, plates are 

 approaching one another, area is being 

 destroyed, and surface matter is being 

 returned to the interior. Along a third 

 class of contacts, area is neither cre- 

 ated nor destroyed, and the relative 

 motions are horizontal. 



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