48 Gilbert — The California Earthquake. 



Art. II.— The California Earthquake of 1V06 ;* by G. K. 



Gilbert. 



Three days after the California earthquake of April 18, 

 1906, Governor Pardee appointed a commission for its scien- 

 tific investigation. ~No funds were at his disposal to defray the 

 expenses, but provision was made later by the Carnegie Insti- 

 tution, and the Institution is publishing the reports. Volume 

 I, in two parts with atlas, has recently appeared, and a second 

 volume is to follow. 



Volume 1 is by Andrew C. Lawson, chairman of the com- 

 mission, and includes contributions from a large number of 

 collaborators. After an introductory account; of the geology 

 and morphology of the Coast Ranges, it treats at length of the 

 physiographic features and physical changes associated with 

 the earthquake, of the distribution of intensity, and of the 

 directions of vibratory motion. The marine phenomena, the 

 composition of the main shock, the sequence of after shocks, 

 and various minor topics are presented, and account is given of 

 earlier severe earthquakes in the same region. 



The earthquake was of the tectonic class, and was occasioned 

 by a slipping on the plane of an old fault. The fault outcrops 

 at the surface, and there was a visible displacement of consid- 

 erable amount. The line of outcrop trends NW.-SE., and 

 the fault plane is vertical. There was, however, very little 

 vertical displacement, the differential movement being almost 

 wholly horizontal. The country adjacent to the fault on the 

 SW. side moved bodily toward the NW., and the country 

 on the NE. side moved toward the SE. The changes did 

 not tend to increase the height of a mountain or the depth of a 

 valley but merely to distort the land horizontally. The amount 

 of displacement was measured in two ways, (1) by observation 

 of the dislocation of roads, fences, etc , traversed by the fault, 

 (2) by the remeasurement of a net of triangulation previously 

 made by the Coast Survey. Fences and roads were usually 

 offset from 8 to 15 feet, and the results from triangulation 

 showed relative dislocation of about the same amount for 



* The California Earthquake of April 18, 1906. Report of the State Earth- 

 quake Investigation Commission. In two volumes and atlas. By Andrew 

 C. Lawson, chairman, in collaboration with G. K. Gilbert, H. F. Eeid, 

 J. C. Branner, H. W. Fairbanks, H. 0. Wood, J. F. Hayford and A. L. 

 Baldwin. F. Omori, A. O. Leuschner, George Davidson, F. E. Matthes, E. 

 Anderson, G. D. Louderback, R. S. Holway, A. S. Eakle, R. Crandall. G. F. 

 Hoffman, G. A. Warring, E. Hughes, F. J. Rogers, A. Baird, and many others. 

 Vol. I, pp. xviii + 451. 146 pis. Atlas, 25 maps, 15 pis. seismograms. 

 Washington, D. C, 1908. (Published by the Carnegie Institution of Wash- 

 ington.) 



