EVIDENCE FROM EARTHQUAKES 173 



measure the actual vertical displacement was limited to those relatively 

 rare localities where offsetting of beds was observable on the fault-plane. 

 The faults which appear at the earth's surface at the time of an earth- 

 quake were until recently regarded as a consequence rather than a cause 

 of the earth's shocks, and hence they were not regarded as true disloca- 

 tions within the earth's shell comparable to those uncovered by extensive 

 denudation. So soon as they are recognized as elements within the earth's 

 fracture system, they may be appealed to for information concerning 

 those properties of a fault not often revealed under other circumstances. 



NoiD, it is a fact of much significance that all "earthquake faults" dis- 

 :lose the same abrupt changes in vertical displacement which are indicated 

 on the faults of the ahove described model, as well as by the faults of the 

 Pomperaug Valley. 



The first earthquake fault to be carefully studied, if we except the one 

 formed in New Zealand in 1855 and mentioned by Lyell in his Prin- 



Sca/e o /Mile 



Figure 43. — Map of the Chedrang Fault 



The faults opened In Assam on June 12, 1897. The vertical displacements are shown 

 at different places along the course of the fault. (After Oldham) 



ciples,^^ was that opened in the ISTeo Valley, Japan, in 1891, of which the 

 beautiful photographs published by Milne and Burton^* attracted at the 

 time considerable attention. Koto®^ tells us that at Katabira the east side 

 of the fault was downthrown. At Midori, five kilometers farther north, 

 the west side was the one downthrown and by the maximum amount 

 (about 18 feet), which was anywhere observed on the entire length of the 

 fault. Again, at Itasho, about one and a half kilometers farther north, 

 the downthrow was once more on the east side. 



The Baishiko fault, which was opened in Formosa during the earth- 

 quake of March 17, 1906, showed a similarly abrupt change in vertical 

 displacement. At Bisho, near the east end of the fault, the nortli limb 

 was downthrown 6 feet, whereas to the west, two-thirds of a mile at 



83 Vol. 2, pp. 82-89. 



^ The great earthquake of Japan. Yokohama, 1891, pp. 1-10, 39 pis. and map. 

 85 On the cause of the great earthquake of central Japan. Jour. Coll. Scl. Imp. Univ. 

 Tokyo, vol. 5, 1893, pp. 339-340, pi. 29. 



