SEISMOLOGY. 363 



membership Professor A. C. Lawson, of Berkeley, Dr. Ralph Arnold, of Los 

 Angeles, Mr. Fred P. Vickery,of the Southern Branch of the University of 

 California, and Mr. L. S. Noble, of the U. S. Geological Survey, has been very 

 active during the past year and has concluded in a most satisfactory manner 

 the first chapter of its task. Although pressed for time and without adequate 

 personnel for so comprehensive a survey, this committee has managed to 

 bring together all of the available information pertaining to the location of 

 known fault lines in California, and the Seismological Society has published 

 it as a supplement to its March Journal (1923). 



It is a natural consequence of somewhat hasty preparation that some of 

 these fault zones have been much more carefully studied than others. It also 

 happened that the group of geologists working in the northern part of the 

 State and the group working in the southern part did not adopt exactly the 

 same system of definitions, but these are minor limitations when compared 

 with the amount of information which has been brought together. The 

 picture here displayed of the zones of structural weakness along the west 

 coast is most illuminating and serves to emphasize very clearly that here is a 

 region where readjustments of considerable scope are in progress. 



The Seismological Society of America has done a very great service to 

 California and to all students of seismologic problems in bringing this 

 information together, and when further studies have prepared the way for a 

 second and more complete edition of this map a new era in the study of these 

 hitherto somewhat mysterious phenomena, which, in this region, have such a 

 direct bearing upon human safety, will have been inaugurated. It is just 

 here that earthquake prediction attains its first significance — prediction not 

 in time but in space, which is much more important; the regions where 

 earthquakes are likely to occur are here plainly indicated. 



Upon this same map there has been incorporated the new group of undersea 

 contours, prepared from five thousand new soundings made by the Hydro- 

 graphic Office of the Navy Department and covering an area of about 34,000 

 square miles, which displays the conformation of the ocean floor adjacent 

 to the fault zones of the Cahfornia coast region. This is the most elaborate 

 study of submarine contours ever attempted. It has not only served to 

 delineate effectively the continental shelf, but also to indicate many 

 major displacements, the relation of which to the land faults is of great 

 importance. From the heights of the Sierra to the foot of the conti- 

 nental shelf is a difference of elevation of more than 25,000 feet 

 (5 miles) within a distance of no more than 232 miles. That such extreme 

 differences of loading within a small area should produce strains which 

 occasionally demand release is in no way surprising. Indeed, it serves 

 to emphasize in an unmistakable manner the need for a systematic study of 

 these strains and their readjustment. It is hoped that the Navy Department 

 will find opportunity to continue these soundings along the entire west coast 

 of the United States (including Panama), and as the power of its ingenious 

 sounding device is increased to extend them to greater depths. The com- 

 mittee is under great obligation to the Navy Department and to Captain 

 F. B. Bassett, Chief Hydrographer, for their keen interest and cordial coopera- 

 tion in the pursuit of this problem. 



