392 CARNEGIE INSTITUTION OF WASHINGTON. 



It is of particular importance that this triangulation will be completed at 

 a time when no great earthquake has occurred for many years. The obser- 

 vations of 1907 were made immediately following the great earthquake of 

 1906. If the earth's crust had been seriously strained by drift and the great 

 earthquake represented the release of that strain through fracture, no informa- 

 tion regarding the character or direction of the strain would be gained by 

 position measurements immediately after the release. If such a drift has 

 continued since 1906, as the observations of the astronomers indicate, we 

 have now the opportunity of locating essential points in the region at a time 

 when the strain is probably considerable. 



3. Southern California. 



The preparation of prehminary plans for work in southern California has 

 been in the hands of the Research Associate in Seismology of the Carnegie 

 Institution, Mr. H. O. Wood, in collaboration with the California Sub- 

 committee on Fault-zone Geology. During the past year Mr. Wood has 

 devoted his whole time (1) to the development of appropriate instruments 

 for the study of tremors, of which more detailed information follows ; (2) to a 

 field study of the southern portion of the State, with a \'iew to the appropriate 

 location of triangulation points for the Coast and Geodetic Survey as soon as 

 it is prepared to extend its work to this region; (3) to mapping the zones of 

 structural weakness in a part of the State in which more extensive and intricate 

 faulting has occurred than elsewhere, and which happens not to have been so 

 extensively studied hitherto as the more northern portions. For the same 

 reason a considerable proportion of the time of Messrs. L. S. Noble and W. 

 S. W. Kew, of the Geological Survey, has been given to this region. These 

 studies are to be continued by the same individuals during the coming year 

 and will result in very careful preparation not only for the triangulation work 

 of the Geodetic Survey, but also for the establishment of stations mounting 

 the instruments through which it is proposed to locate the origin of land-slips 



and tremors. 



4. The Development of Instruments. 



The development of instruments of appropriate sensitiveness to detect local 

 shocks of short period appears never to have been seriously undertaken in 

 seismology, but in the success of this particular research it was thought to be 

 the most vital factor. Dr. J. A. Anderson, of this committee, has given much 

 attention to the subject throughout the year. Associated with him were Mr. 

 Wood, whose experience was most valuable because of his attempt to record 

 such shocks emanating from the volcanoes of the Hawaiian Islands during the 

 period from 1912 to 1917; Mr. Francis G. Pease, of the staff of the Mount 

 Wilson Solar Observatory, who designed the system of chronographic 

 registration; Dr. Frank Wenner, of the U. S. Bureau of Standards, who has 

 had especial success in the development of galvanometers for such unusual 

 purposes, and who undertook a special trip to California under leave of absence 

 from his duties in Washington to associate himself for a time with this enter- 

 prise; Professor Arnold Romberg, of the University of Hawaii, who has given 

 several years of study to this problem of seismographic record in connection 

 with his studies of Hawaiian earthquakes; and finally. Professor Milhkan, of 

 this committee, who, with his associate in the California Institute of Tech- 

 nology, Dr. W. T. Whitney, and his skilful mechanician, Mr. Pearson, under- 



