. Bulletin of the Geological Society of America. Geology. 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'
. Bulletin of the Geological Society of America. Geology. 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 abr
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