THE EARTHQUAKE RIFT OF 1906 307 



ported the matter at Unalaska, the water was so hot that a vessel could 

 not approach within five miles of the island. It is conceivable that' 

 the great earthquake rift has its center in the area of weakened sea- 

 bottom occupied by the Bogoslofs. It is possible, even probable, that 

 the coincidence of time does not show any real connection between 

 Bogoslof and the earthquake of 1906. Against the connection may be 

 urged the great distance, the great depth of most of the intervening 

 sea, and the alleged facts that the seismograph at Sitka showed a shock 

 from the south, while that at Tokyo indicated waves from the east. It is 

 also stated that no shock was felt at St. Paul, St. George or Unalaska, 

 but that a great shock was felt at Unimak. Unimak, like Unalaska, 

 lies to the east of the supposed line of the fault. In any case, the birth 

 of the third Bogoslof is a matter worthy of thorough investigation, and 

 its approximate coincidence in time with the earthquake in California 

 is very suggestive. 



The earthquake of 1906 is receiving the most thorough study pos- 

 sible, and in such a way as to give promise of important practical 

 results. The many previous earthquakes have been recorded, but their 

 most essential feature, the location and extent of the causing fissure 

 has rarely been indicated. In the records we read again and again 

 that ' fissures opened in the ground,' but whether these were rifts in 

 the crust or mere slumps of soft ground as a rule has escaped attention. 

 The great earthquake of 1868 opened rifts at intervals from Tomales 

 Bay to Carisa Plain, and also a fissure on the east side of San Fran- 

 cisco Bay, where a straight crack about ten miles long extended 

 from Haywards toward the south. One side of this rift showed a 

 lateral displacement of about four feet. To this short rift, rather than 

 to the Portola-Tomales fissure, the shock in San Francisco in 1868 may 

 have been due. The shock in that year was more violent in Oakland 

 than in San Francisco and most violent about San Leandro and Hay- 

 wards, to the south of Oakland. It is conceivable that the shock of 

 1865, having its center in the Portola fault, not far from San Fran- 

 cisco, gave that city a degree of immunity in 1868. Other destructive 

 earthquakes, as recorded by Holden {' Catalogue of Earthquakes on 

 the Pacific Coast, 1769 to 1897') are as follows: 



1800. This earthquake was severe about San Juan Bautista, but whether 

 in the Portola fault or the Pajaro fault is not clear. 



1812. This earthquake wrecked the mission of San Juan Capistrano in 

 southern California, and was felt along the line of the southern missions. It 

 had its center possibly in the Santa Catalina Channel. 



1818. This earthquake injured the mission of Santa Clara; hence it may 

 have been along the Portola fault. 



1836. This was said to be similar to the shock of 1868, its center along 

 the Portola line; 'great fissures were made in the earth.' 



1839. This was severe from Redwood to San Francisco, 'a great fissure 

 opened to Mission San Jose.' It was probably also in the Pajaro fault. 



