EARTHQUAKES ON THE PACIFIC COAST 7 



1897. June 20; San Francisco; 12:14:40 p. m. Lasted 20 seconds; severe 

 shock.— Prof. A. G. McAdie. 



F. W. Edmonds, of U. S. Coast and Geodetic Survey, says there was 

 a slight shock at 6:37 a. m. There was a tremor at 12:59 p. m. 

 This shock stopped many clocks in San Francisco. Most of these 

 stopped at 12:13 p. m. This disturbance was felt at Oakland, 

 Berkeley, Campbell, Centerville, Hollister, Milton, Eio Vista, Sacra- 

 mento, San Jose, San Leandro, Santa Cruz, Stockton, Napa, Niles, 

 Mount Hamilton, College Park, Mills College, Gilroy, Salinas, Los 

 Gatos, Templeton, Monterey, Pacific Grove, Modesto, Newman, 

 Cantau Creek, Merced, Visalia, Santa Eosa, Haywards, Decoto, 

 Watsonville, Hanford, Fresno, Gonzales, Eedwood City, San Eafael. 



Lick Observatory; 12:12:55 to 13:5 p. m. Direction, northeast and 

 southwest; heavy; rocked pictures on the wall. Prof. W. W. 

 Campbell. Both Ewing and duplex seismographs recorded the 

 shock, record of duplex not complete; pen obstructed. The 

 record is 16 mm. in length and north and south direction and 9 

 mm. east and west. The Ewing instrument gave all three com- 

 ponents; duration slightly over 30 seconds; waves of considerable 

 amplitude and slow, the greatest motion being east and west. 

 The heaviest wave seems to have occurred one second after the 

 commencement of the shock, the amplitude magnified being 16.3 

 mm., or an earth motion of 4.1 mm. east and west. There is also 

 a north and south component of this wave of 6.3 mm. magnified, 

 corresponding to an earth movement of 1.5 mm. Hence the great- 

 est double amplitude of this wave is 4.4 mm. with a period of 

 1.5 seconds, which gives an intensity of 39 mm. per one second, 

 or 11 on the Eossi-Forel scale. The next move recorded by the 

 east and west pen is probably the one of greatest intensity, 

 although of small magnitude; amplitude, 0.25 mm.; time, 0.37 

 second, from which intensity would be IV on the E.-F. scale. 

 The greatest vertical disturbance occurred about the middle of 

 the shock, when the record showed four waves of 4 mm. double 

 amplitude magnified with an average period of about 2 seconds. 

 The whole shock exhibits marked irregularities; none of the waves 

 are smooth, but all have lesser vibrations superposed upon the 

 larger. 



College Park. The seismograph at the University of the Pacific 

 registered the shock. The tracing is very complicated and is three 

 times the size of the tracing by a similar instrument at the Lick. 

 The axis of greatest disturbance is northwest and southeast, the 

 record measuring 50 mm. in this direction. At right angles to 

 this the record measured 28 mm. Allowing for a magnification 

 of 4.0 diameters, this makes the greatest actual motion of the 

 earth about 12 mm. 



Mills College, 12:13 p. m. Severe, set chairs to rocking; double,, 

 the latter part being heavier. Total length of tracing northeast 

 and southwest is 30 mm. and at right angles to this 18 mm. A 

 compact mass of vibrations covering 8 mm. in diameter, fronu 



