THE 



POPULAR SCIENCE 

 MONTHLY 



OCTOBER 1906 



THE EARTHQUAKE RIFT OF 1906 



BY President DAVID STARR JORDAN 



LELAND STANFORD JUNIOR UNIVERSITY 



r | ^HERE are two sets of disturbances which shake the crust of the 

 -*■- earth and therefore go by the name of earthquakes. Eruptive 

 earthquakes are explosions, usually of steam, about a volcano. Tectonic 

 earthquakes are breaks in the overloaded or overstrained crust of the 

 earth, and, for the most part, have nothing to do with the steam vents 

 we call volcanoes. To the last class most earthquakes belong, certainly 

 almost all that have been felt within the tmited States. 



Again, under the name of earthquake we include two very different 

 sets of phenomena, the one the rock-rift or fault, which is the disturb- 

 ance itself, the other the spreading or interfering waves set in motion 

 by the parting, shearing and grinding of the sundered walls of rocks in 

 the earthquake fault. It is the jarring waves extending in widening 

 and interfering circles which do the mischief to man and his affairs. 

 It is the rift of rock which sends these waves forth on their blind 

 mission of confusion or destruction. 



In every tectonic earthquake there is somewhere a fault or rift of 

 rock, with some sort of displacement, permanent or temporary, of the 

 relations of the two sides. In extreme cases, this break extends for 

 miles in a straight line, breaking the surface soil and passing down- 

 ward to a depth which can be only guessed at, five or ten miles perhaps, 

 perhaps as far down as the crust is rigid. There are undoubtedly 

 destructive earthquakes in which the soil is not broken over the rift of 

 rock, but as a rule, in violent disturbances, the crack comes to the sur- 

 face, breaking through the overlying soil. In all severe earthquakes 

 there are, moreover, breaks or fissures in the earth having no connection 

 with the fault itself. These are slumps or landslides, and geologically 



VOL. LXIX. 



19. 



