BARYSEISMIC DISTURBANCES 883 



be deepseated or may reach the surface. The depth to wliich the 

 dislocation penetrates may be very great — it may pass from the 

 zone of fracture into that of flowage ; but the origin of the shock 

 is probably never deeper than 30 geographical miles, and usually 

 does not exceed 5 to 15 miles. (Hovey-21 '.2^4.) The point or 

 locus of origination of the earthquake is variously called the 

 seismic center, centruui, hypocentcr, origin, or focus. This, though 

 conveniently regarded as a point, is really a space of three dimen- 

 sions which in different cases varies much in size and shape and 

 may be of great magnitude. The part of the earth's surface which 

 is vertically above the center is the epicenter or epicentral or epi- 

 focal tract. 



Surface Manifestations of Barvseismic Disturbances. 



The surface manifestations of an earthquake-producing fault 

 or other tectonic movement may, so far as the lithosphere is con- 

 cerned, be classed as rifting, as slipping, and as disruption. The 

 first is mere separation, the second involves displacement. It is to 

 the latter movement that the term faulting is commonly applied. 



Rifting. 



As a result of rifting, fissures will open in the earth (Fig. 240) 

 and these may remain open or be filled by injected material. So 

 far as arrangement is concerned these fissures may be in parallel 

 series, as in the case of the fissures formed by the earthquake of 

 Sinj, Austria, in 1898, in which slipping also occurred along each 

 rift. Or, again, these fissures may radiate from a center, branch- 

 ing repeatedly. Such fissures were formed during the Calabrian 

 earthquake of 1783. Finally, fissures formed during earthquakes 

 may be irregularly intersecting, forming a network. This type has 

 been observed at Aigon in the Balkans after the earthquake of 

 December 26, 1861 ; in Owens \^alley, California, after the earth- 

 quake of 1872 (Whitney) ; and in Ecuador, where it is a very 

 characteristic feature of the Andes region. Whimper (43) says of 

 these: 'Tn no other part of Ecuador is there anything equaling 

 this extraordinary assemblage of fissures, intersecting one another 

 irregularly and forming a perfect maze of impassable clefts . . 

 the cracks are all A'-shaped and, though seldom of great breadth, 

 are often very profound, . . Several, at least, have been 



formed within the memory of man, while others arc centuries old." 



