890 PRINCIPLES OF STRATIGRAPHY 



Even greater distances have been traveled by tsunamis, as, for 

 instance, those originating in an earthquake at Concepcion, Chile, 

 which "set in motion a wave that traversed the ocean to the Society 

 and Navigator Islands, 3,000 and 4,000 miles distant, and to the 

 Hawaiian Islands, 6,000 miles." (Dana-5 :2/j.) 



The velocity of these mighty waves has been ascertained, and 

 is seen to be far greater than that of ordinary sea-waves, though 

 it does not equal that of earthquakes proper. "The waves of the 

 Japan earthquake crossed the Pacific to San Francisco, a distance of 

 4,525 miles, in a little more than twelve hours, and, therefore, at a 

 rate of 370 miles per hour, or over six miles per minute. The 

 waves of the South American earthquake of 1868 ran to the 

 Hawaiian Islands at a rate of 454 miles per hour." (Le Conte- 

 26:131.) _ 



Seismic disturbances are not confined to the shore, however, 

 but also occur under the sea. Both pyroseismic and baryseismic 

 disturbances are likely to afifect the water and produce pronounced 

 disturbances. That faulting occurs on the bottom of the deep sea 

 is shown by soundings and studies of cable routes. The frequent 

 breaking of the cables, accompanied by thrusting and fraying, fur- 

 nishes visible evidence of such disturbances. Precipices from 3,000 

 to 5,000 feet in height have been detected by soundings in the 

 Mediterranean, a difference in depth of 2,000 feet having been 

 noticed between the bow and the stern of the cable repair ship. 

 The earthquake of October 26, 1873, caused the cable to break 7 

 miles from the cable office at Zante, Greece, by the formation of a 

 submarine fault scarp 600 feet in height, the change in depth being 

 from 1,400 to 2,000 feet. Similar breaks, with the formation of 

 submarine fault scarps more than a thousand feet in height, have 

 been reported from the same region. Submarine earthquakes 

 ought to be distinguished from sea-quakes proper. The latter 

 always accompany the former and may even accompany earth- 

 quakes originating in the land near the sea. On the other hand, 

 true sea-quakes, or thalassoseisma, may be formed by causes which 

 will not produce earthquakes, as, for example, submarine explosions. 

 The latter represent a submarine pyroseismic disturbance (whether 

 of a submarine volcano or a submarine mine), and this is the only 

 kind of directly induced sea-quake or thalassoseisma possible. Sec- 

 ondarily induced or communicated thalassoseisma are, however, the 

 most frequent type, and here belong, besides the effects of many 

 volcanic explosions on the sea coast (e. g., Krakatoa), the great 

 series of baryseismic disturbances or tectonic faultings. 



