46 



SMITHSONIAN MISCELLANEOUS COLLECTIONS 



in California occurred apparently without any relation to pres- 

 sure distribution. It was noticed, however, that some earthquakes 

 occurred during the passage of a marked ' ' high ' ' across the 

 northern portion of the coast. While any relation of this charac- 

 ter must be obscure and indefinite, it is conceivable that in a 

 region where quakes and tremors of tectonic origin are frequent — 

 that is, a region where strata are in unstable equilibrium — the 

 passage of an area of high pressure may directly or indirectly 

 affect the stresses at critical times. The relation is involved and 

 is alluded to here only because at Manila and Tokyo microseismic 

 phenomena bear some relation to approaching typhoons: The 

 thought suggests itself that the installation of seismographs on 

 the Pacific coast may lead to the detection of advancing pressure 

 areas. 

 The earthquake, as timed by the writer, began at 5:13:05 a. m., 120tli 

 meridian time. The disturbance lasted for about 40 seconds. The 

 main shock was followed by others. The times are: 

 April 18, 1906, 5:13:05-45 (?), severest known in San Francisco. 

 " 5:19:10 a. m., feeble. 



" " 5:21 a. m., feeble. 



" " 5:26 a. m., feeble. 



" " 5:43 a. m., feeble. 



" " *[6:06— 6:30— 6:42 and 6:56 light]. 



" " 8:14:28 to 8:14:33, sharp, twisting motion. 



" " *[8:19— 8:42]. 



" " 9:14 a. m., sharp, short. 



" " 9:26 a. m., moderate. 



" " *[9:48 and 10:05]. 



" " 10:50 a. m.. moderate. 



" " 11:06 a. m., moderate. 



" *[11:47]. 



" " 12:04 p. m. 



" " 12:11 p. m., very light. 



" " 2:24 p. m., very light. 



" " 2:28 p. m., very light. 



" " 4:51 p. ni., very light. 



" " 6:50 p. m., very light. 



" " 7:01 p. m., very light. 



April 19,1906, 3:07:00 a. m., light. 



" " 1:13 p. m., sharp, main portion with twist. 



April 20,1906, 4:45:00 a. m., tremor. 



" " 5:31 a. m., moderate. 



" " 7:15 a. m., moderate. 



April 21,1906, 6:28 a. m., strong. 

 April 22,1906, 7:03:00 a. m., light. 



" " 3:19:30 p. m. to 3:19:34 p. m., moderate, rocking. 



April23, 1906, 12:05:00 a. m., lasted about 3 seconds. 



" " 3:51 p. m., sharp, downward jolt. 



" " 10:34 p. m., moderate. 



♦[Obtained by voltmeter diagrams furnislieil by Mi-. Nelson Eckart.J .411 other times by the 

 writer. 



