SEISMOLOGY. 365 



a detailed geological study of this region. This work has been continued 

 throughout the past year by Noble and Kew; and so far as it has revealed 

 active faults, they have been made a matter of record and incorporated in the 

 fault map above mentioned. 



Particular attention has been given, this year as last, to the San Andreas 

 rift zone, and a considerable amount of new information has been gathered 

 regarding its exact location and the recent activity there. It has been the 

 plan from the beginning to place in this region the first installation of seis- 

 mologic instruments for the detection of local movements as soon as the 

 instruments should be ready. It is therefore of prime importance that 

 our geologic knowledge of the region should be as complete as possible in order 

 that the tremors which it is proposed to trace there may be intelligently ob- 

 served. During the present season the detailed mapping will probably be 

 carried over the San Gorgonio Pass through one of the most interesting regions 

 along the entire path of the San Andreas fault. To the U. S. Geological Survey, 

 under whose auspices Messrs. Noble and Kew have been able to give so much 

 time to the problem during the past two years, the committee is indebted 

 for contributing one of the most interesting features of the investigation. 



During the last half of the year Mr. Wood has not been able to give as much 

 time to this survey as formerly, because the newly developed instruments, 

 of which some description will be given below, are now in actual operation, 

 and the study of their behavior and of the character and scope of the results 

 which can be obtained with them has required constant attention since 



January. 



4. The Chilean Earthquake of 1922. 



We were particularly fortunate in obtaining from the Carnegie Corporation 

 of New York a special grant of S5,000 for the study of the great earthquake 

 which occurred in Chile on November 10, 1922. Situated as it is on the west 

 coast of the American Continent, like California, it was thought that a study of 

 this destructive shock in Chile might throw considerable light on the Cali- 

 fornia problem before us, while the California observations in turn might 

 help to elucidate a similar problem in South America. The two situations 

 did not prove to be as closely analogous as was anticipated, but the experience 

 from each proved of value to the other. 



Professor Bailey Willis, of this committee, spent six months (February to 

 August 1923) on the ground in a careful examination of the visible evidences 

 of the movement and of the geological formations of the region. He was 

 accorded the fullest support and in many cases the close personal coopera- 

 tion of officers of the government, of scientific bodies, and of commercial 

 organizations. His Excellency the Ambassador of Chile at Washington, Dr. 

 Beltran Mathieu, Dr. Xavier Gandarillas, Director of the Bureau of Mines 

 (Santiago), Dr. Francesco Mardones, who has since become Minister, the 

 Director General of State Railways, Don Rudofifo Jaramillo, and Dr. Johann 

 Felsch, a geologist of the Bureau of Mines, were particularly helpful. Dr. 

 Willis's conclusions will be found on pages 368 and 369. 



5. The Development of Instruments. 



The report of last year records the fact that after a conference between 

 Dr. J. A. Anderson, of this committee, Mr. Wood, and a number of physicists 

 of considerable experience in seismologic research, a new design of instru- 

 ment of the Galitzin type was agreed upon and construction begun in the 



