566 Reports and Proceedings — Geological Society of London. 



1890-1 was little, if at all, clue to the marked shock of May 12, 

 1889, but that the earthquakes of these years were preparatory to 

 the great earthquake, the consequent relief at numerous and widely 

 distributed poiuts equalizing the effective strain along the whole 

 fault-system, and so clearing the way for one or more almost 

 instantaneous slips along its entire length. This outlining of the 

 fault-system points to the previous existence of the faults, and 

 implies that the great earthquake was due not to the rupturing of 

 the strata, but probably to the intense friction called into action 

 by the sudden displacement. 



The distribution of the after-shocks is then discussed, and it is 

 maintained that the after-shocks of the Mino-Owari earthquake for 

 the first fourteen months were subject to the following conditions — 

 decline of frequency, decrease in the area of seismic action, and 

 a gradual but oscillating withdrawal of that action to a more or less 

 central district. 



Professor John Milne, F.R.S. (who has lately returned from 

 Japan and intends now to reside in this country), said that the 

 Mino-Owari earthquake had furnished a greater number and a more 

 varied series of seismic phenomena for analysis than had been 

 noted in connection with any disturbance previously recorded. 

 When this earthquake took place an enormous fault, which can he 

 traced over a length of more than forty miles, appeared upon the 

 surface, and it was usually supposed that the sudden rupture and 

 displacement of vast masses of material along this line were the 

 cause of the earthquake. 



On account of a peculiar distribution of shocks which took place 

 prior to 1891, Mr. Davison argued that the fault or faults in the 

 Mino-Owari district were outlined before the occurrence of the great 

 earthquake, which was, therefore, only the result of their extension. 

 This may have been so, but it must be remembered that before 1891 

 the number of shocks occurring in the Mino-Owari plain were not 

 numerous; and as we pass from 1889 to 1891 we cannot say that 

 they increased in number, while their distribution, as exhibited by 

 maps, was largely dependent upon the observing-stations. Where 

 the maps showed blank spaces, in many cases the country was 

 mountainous, and there were no observers. The present author's 

 method of treatment of the statistics relating to " after-shocks " no 

 doubt possesses advantages over that previously used by Professor 

 Omori, but the results arrived at, so far as they are comparable, 

 closely accord. It was at the speaker's suggestion that the study of 

 after-shocks was taken up, and he must congratulate Professor 

 Omori at having obtained results far beyond and of greater im- 

 portance than anything anticipated at the outset. Professor Omori 

 added to our knowledge respecting the expiring efforts in a seismic 

 area; while Mr. Davison, amongst other things, has thrown new 

 light upon the change in subterranean conditions which culminated, 

 on October 28, 1891, in a shaking which could be recorded from 

 pole to pole. 



