330 B. KOTO: CAUSE or THE GKEAT 



VI. The Course of the Line of Ihe Great Fault that 

 caused the Earthquake. 



The Gfreat earthquake of Centra] Japan sliook the extraordinarily 

 Jarge superficies of 24o, 055 square kilometres, or more than tln-ee-fifths 

 of all Japan, and must be counted as one of the greatest physical 

 events of modern times. Let us see now how the fault looks which 

 produced such a tremendous effect ? 



Faults or throws may be observed a.lmost everywhere in the 

 earth's crust, and geologists and miners are quite familiar with 

 their structure. But it rarely happens that a, fault comes into 

 relief in complicated mountainous districts. In less disturbed regions 

 such as the l^lateau of Colorado, or the eastern border of the Central 

 Asiatic plateau, the lines of displacement can be traced with great 

 certainty ; and the underground structure is usually reflected in a 

 great measure in the topography of the region concerned. In 

 the Alps and Central Europe, most of the earthquakes have hitherto 

 been ascribed to a tectonic movement of the solid crust through lineal 

 extension of the disturbed area, but no actual fault has anywhere 

 l:)een found which was formed at the time of an earthquake, and 

 could be reasonably assumed to be the originator of the disturbance. 



The case of 1891 /.s quite otlienrise. Here ire could not onh/ 

 positirehi ohserve the fault on tlie surface, hut also measure tlie height 

 anil length of it. At a place called Midori in the Xeo valley, the 

 flat bed of the valley was split longitudinally, and one side was 

 tipped off so that there is an abrupt step, measuring 5.5 to 6 metres 

 verticall}^ The earth very regularly took its angle of repose at the 

 break ; and the appearance, as we come to it eastwards from below, 

 is as if we were approaching a r:!ilway embankment (PL XXXn"^.). 



