EARTHQUAKES ON THE PACIFIC COAST 131 



onds. The period of each wave was about 1.7 seconds, which is 

 very gentle and slow, and the double amplitude of the vertical 

 waves was never more than 0.03 of an inch. The east and west 

 movement consisted of strong tremors for nearlj^ foiir seconds, 

 when the waves began and lasted, as strong decided movements, 

 for twenty-nine seconds, after which the tremors continued until 

 their trace was lost. Ninety seconds after the beginning, the 

 period of these waves is 0.8 of a second (very slow) and the 

 double amplitude is about 0.03 of an inch. The most remark- 

 able motions were in the north and south direction. The tremors 

 were felt for three seconds, ten large waves for forty-five sec- 

 onds, succeeded by tremors until one hundred and thirty-two 

 seconds from the beginning. Their period was 0.6 of a second. 

 The double amplitude is 0.05 of an inch. The duplex machine 

 shows results agreeing with the above and indicates the verj^ 

 complex nature of the motion of the ground. 



The vibration of greatest amplitude occurred only five seconds after 

 the plate of the Ewing seismograph started, and is nearly as 

 great in the east and west as in the north and south curve, 

 while the vertical component is small. Paying due regard to the 

 values of the different components, it appears that the maximum 

 vibration (double amplitiide) of the earth at the Lick Observatory 

 was 2.2 millimeters, and the period being 0.6s. as stated above, 

 the computed intensity of the shock is 120 or (V) of the Rossi- 

 Forel scale. 



Yerba Buena Island Light Station, San Francisco Bay; time, 3.14 

 a. m.: from eight to twelve seconds duration; one long, rolling- 

 shock with a sort of jumping motion also, but it still can only be 

 called one shock; lighthouse clock did not stop; the motion was 

 certainly from east to west; no damage. — J. A. F. McFarland. 



Mare Island Light Station; time, 3.9.30 a. m. : observer was awak- 

 ened. The shock was intermittent; door-bell rang in a house 

 near hj (VI). — Kate C. McDougal, light-keeper. 



Berkelej^: in the valleys the shock was more severe. The seismo- 

 graph tracing of the university observatory at Berkeley shows 

 a very complex curve, which can be rovighly bounded by an 

 ellipse 8 by 6 millimeters, with one great loop extending 7 milli- 

 meters farther (magnified four times). Duration 12 sec. Vibra- 

 tions slow. 



Oakland: the Chabot Observatory record has some resemblance to 

 the above, but is larger, the bounding ellipse being 22 millimeters 

 long, also with a loop extending toward the northwest. The 

 mean-time clock of the Chabot University stopped at 3.01.44 

 (VI).— C. Burckhalter. 



East Oakland: the record obtained at Mr. Blinu's observatory some- 

 what resembles that just described, and indicates a shock of 



