134 



SCIENCE 



[N. S, Vol. XXIX. No. 734 



MOKAL 



It remains to draw the moral. In view 

 of these facts as to forecasting, and of the 

 further fact that we have in our land a 

 district subject to strong earthquakes, 

 there are duties to be recognized and 

 policies to be advocated. It is the duty 

 of investigators — of seismologists, geolo- 

 gists and scientific engineers — to develop 

 the theory of local danger spots, to dis- 

 cover the foci of recurrent shocks, to de- 

 velop the theory of earthquake-proof con- 

 struction. It is the duty of engineers and 

 architects so to adjust construction to the 

 character of the gi-ound that safety shall 

 be secured. It should be the policy of 

 communities in the earthquake district to 

 recognize the danger and make provision 

 against it. 



The general fact of local danger spots, 

 where the agitation during strong earth- 

 quakes is peculiarly violent, has long been 

 familiar. It is known that they are com- 

 monly found in lowlands where the under- 

 lying formation is a deep deposit of al- 

 luvium or other unconsolidated material, 

 and that such material, while it aggravates 

 great shocks, absorbs and quenches small 

 ones. It is also known that the local 

 phenomena are in some way connected 

 with the transformation of earthquake 

 waves in passing from elastic to inelastic 

 material. But a mechanical theory of the 

 phenomena is yet to be supplied. For 

 economic, as well as scientific purposes, 

 this is one of the important fields for in- 

 vestigation. In Japan, where earthquakes 

 are much more frequent than in any por- 

 tion of our own land, the subject has been 

 studied and may still advantageously be 

 studied, by the observation of natural 

 shocks. In America the problem can be 

 more readily studied by means of artificial 

 earthquakes in the laboratory, continuing 

 the line of experimentation begnin by 



Kogers." When the underlying prin- 

 ciples have become known, it wiU be com- 

 paratively easy for geologists, engineers 

 and architects to estimate the danger fac- 

 tor in places to be occupied by buildings. 



The San Andreas rift,^^ now traced 

 through so much of its length as traverses 

 inhabited areas, is recognized as a danger 

 belt of a peculiar character, to be avoided 

 especially by water conduits and railways. 

 Although it is probably the most extensive 

 rift belt in the country, it is not the only 

 one, and the positions of all others should 

 be determiaed and mapped. The foci or 

 epicenters of recurrent earthquakes are 

 also localities of special danger, even 

 though the underlying formation is firm 

 and elastic. So far as the earthquake 

 faults reach the surface of the ground, the 

 epicentral tracts coincide with the rift 

 belts and fault scarps; but some of the 

 foci are doubtless wholly subterranean 

 and need for their discovery a seismic sur- 

 vey like those conducted in Japan, 

 Italy, England and, since the Valparaiso 

 earthquake, in Chili. In Japan, which 

 now takes first place in the study of earth- 

 quakes, the survey is conducted by a sys- 

 tem of seismographic observatories in 

 cooperation with a large body of local 

 correspondents — a mode of organization 

 quite analogous to that of our Weather 

 Bureau, with its system of thoroughly 

 equipped stations and its wide-spread 

 corps of volunteer observers. 



Much progress has already been made 



"Professor F. J. Eog?rs, of Stanford Univer- 

 sity, gave harmonic motion in a horizontal direc- 

 tion to a box of sand, and found that under cer- 

 tain conditions a body resting on the sand received 

 motion which was not harmonic, and which had 

 greater amplitude and a much greater maximum 

 acceleration than the motion of the box. His 

 experiments are described in the "Report of the 

 California Earthquake Commission," Vol. I., Part 

 II., pp. 326-35. 



" " The California Earthquake Investigation 

 Commission," Vol. I., Part II., pp. 25-53. 



