DISLOCATIONS 



Slipping. ■ 



When differential movements of the two sides of a fracture 

 occur a fault results. This movement may be horizontal, diagonal, 

 or vertical. The displacement may be profound or very slight. It 

 may be sudden or by a series of progressive slips, or it may be 

 the resultant of a series of slips in various (even opposite) direc- 

 tions, and of varying amounts. The California earthquake of 1906 

 and the Japanese earthquake of 181 1 were caused by slips of large 

 amplitude along well-defined seismotectonic lines. The frequent 

 New England quakes are due to a relatively large number of slight 

 adjustments along joint planes. These minor slippings may be 

 so slow as to produce no perceptible seismic disturbances, though 

 they may find a surface expression in minute faults. Here, prob- 

 ably, belong the numerous minute post-glacial faults of New Eng- 

 land and eastern New York. (Woodworth-45.) 



The local rise and fall of the land in response to adjustment 

 to stresses, but without violent shocks, or abrupt ruptures, may 

 be considered as forming one end of the series of earthquake- 

 producing disturbances. To these the name bradvseisms has been 

 given, and they are well illustrated by the changes of level re- 

 corded in the ruins of the Temple of Jupiter Serapis in the Bay 

 of Naples, already referred to in an earlier chapter. 



On the surface the fault is expressed by the dislocation of 

 structures, such as fences, roadways, and parts of buildings, bridges, 

 railroad tracks, or of natural objects, such as trees, etc., while if 

 the slipping has a vertical component, a fault scarp will result. 

 These phenomena, and the types of faults and their effects, have 

 been discussed in Chapter XXI. When successive shocks from 

 various directions are experienced, a vortical movement of objects 

 may result, as in the case of statues turned on their pedestals. 

 The various effects of such shocks on buildings and other structures 

 are fully illustrated in the reports on the recent Calif ornian and 

 other earthquakes. 



Block Movement. The faulting may be manifested as a block 

 movement, strips of land dropping or rising and forming rift 

 valleys (Graben) or fault blocks. On a large scale, these form 

 fault-block mountains. Such faulting occurred in connection with 

 the Owens Valley earthquake of 1872, the resulting scarps reaching 

 in some cases a height of ten feet or more. At Big Pine. Califor- 

 nia, a tract of land 200 to 300 feet wide sank, some portions being 

 depressed 20 feet or more, leaving vertical walls on either side. 



