374 ANNUAL EEPORT SMITHSONIAN" INSTITUTION, 1931 



formation in the case of the Chile earthquake of 1922 from the fall 

 of boundary walls of adobe. Unfortunately, the bottoms of the walls 

 were weathered and somewhat rounded and this vitiated the con- 

 clusions. It is obvious that instrumental observations alone will give 

 the true values of the acceleration. Acceleration, however, can not 

 stand alone as the cause of destruction. It is the combination of 

 acceleration, period, duration of the shock, and perhaps the num- 

 ber of periods of strong shock which causes the destruction. Im- 

 amura ^ gives an example of an earthquake occurring in March, 

 1930, in Japan where the recorded acceleration was 0.8 g, but the 

 period and duration were both very short and no serious damage 

 was done. It is obvious that records to be useful must give all these 

 factors accurately. 



These observations, when made, should be competent to decide the 

 question of the existence of surface waves of considerable ampli- 

 tude and of low velocity which have been mentioned. It is also 

 important to learn more about the differences in the effects of earth- 

 quakes which rupture the surface and those which are of great in- 

 tensity but too deep to cause such rupture. Of particular interest 

 are the vibrations set up by visible slipping along a fault plane. It 

 would be of great interest to know just what is the difference in 

 the transmission of energy in earthquakes of this type from that in 

 such cases as earthquakes associated with volcanic eruptions in which 

 the energy appears to go out equally in every direction. 



Observations of a few strong earthquakes in their central regions 

 will not solve all these and other problems. The possible number 

 of combinations are very great. However, with an effective program 

 the accumulation of information will be steady. 



The recent New Zealand earthquake (February 2, 1931) has shown, 

 as have many others, that certain t5^pes of earthquake damage are 

 inevitable. Types of construction matter little if the building is 

 directly over a fault line with horizontal or vertical slipping or in the 

 path of a great landslide. If a great tidal wave occurs buildings in 

 its path will be swept away. However, for most earthquakes the 

 number of buildings exposed to these special hazards is not a large 

 proportion, and the most common needs are ability to resist strong 

 shocks and fire prevention. In both these fields there are important 

 possibilities. Earthquakes are no more numerous or more severe 

 than in the past, but the earth is so much more intensively occupied 

 that the risk of important damage is greater than ever before and 

 is constantly increasing. 



» Imamura, A., and others, On the recent Ito earthquake, Proc. Imp. Acad., vol. 9, 

 No. 5, 1930. 



