378 ANNUAL. REPORT SMITHSONIAN INSTITUTION, 19 31 



quake and tidal wave. This phenomenon has been observed to a 

 lesser degree in other earthquakes, and the natural assumption is that 

 the surface of the earth tilts just before the earthquake. In four 

 earthquakes the intervals have varied from one-half to four and 

 one-half hours. Recently instrumental observations have been made 

 of the tilt of the ground which confirms the earlier observations 

 and indicates that in Japan, at least, the tilting of the ground is 

 significant. This does not refer to local tilts due to temperature 

 which the tilt compensation seismometer eliminates, but it is a long- 

 period tilting of the ground in regions subject to severe earthquakes 

 with rapid tilting just before the earthquake. If it can be definitely- 

 established that this is common to all earthquakes in Japan, even 

 when the amount is less than can be readily perceived, it may be 

 possible to give an advance notice of a few hours which might be 

 invaluable. The Japanese have developed a tiltmeter, and another 

 instrument for this purpose has been designed at the United States 

 Bureau of Standards, but has not yet been constructed. It is im- 

 portant to learn whether this phenomenon is peculiar to Japan or 

 any other region where there is block faulting on a large scale or 

 whether the same thing will be observed in this country. 



My purpose has been to show that a program of earthquake in- 

 vestigation is being developed which, when added to the already 

 well organized plan, will fill important gaps in present knowledge. 

 Stress has been laid on fundamental principles, instruments, and 

 methods, and this serves to emphasize that we are still in a stage 

 when these are the all-important things. We are beginning to 

 utilize the records to find out facts about the earth, but there is 

 great room for expansion in this, field. There are two great fields 

 of investigation — that treating the earth as a whole, or dealing with 

 a substantial portion of its crust such as the area of the United 

 States, and the local investigation as exemplified by the investiga- 

 tions in California under the auspices of the Carnegie Institution 

 of Washington, the California universities, and other organizations, 

 the investigations in the Mississippi Valley under the auspices 

 of St. Louis University and the National Research Council, and 

 the plan of the Coast and Geodetic Surve}^ for cooperative observa- 

 tions chiefly for the benefit of the engineer. 



The studies with regard to the United States as a whole are car- 

 ried on by the National Government through the Coast and Geodetic 

 Survey with the cooperation of the Weather Bureau, the Geological 

 Survey, the Bureau of Standards, and the National Research Council, 

 the members of the Jesuit Seismological Association, and the univer- 

 sities and colleges in different parts of the country. The eventual 

 aim is to keep informed in regard to the elastic condition of the 

 earth's crust. 



