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Transactions .—Geology . 



propagation assumed is 50 miles per minute, and this solu- 

 tion agrees also with Wanganui (8.4), and Westport (8.3) 

 nearly, and is only ^min. out for Picton (8.2). 



(y) The method of co-ordinates : The times in the list 

 {a) — all verified by New Zealand Mean Time, and apparently 

 good times, referring to the same phase of the same shock — 

 were employed. Christchurch was taken as the origin of 

 co-ordinates, the line Christchurch-Hokitika as the axis of y, 

 and the axis of x at right angles (north-easterly). 

 The reduced equations are — 



Opunake), 544^ -f 1967/ -}- iw - ^lu = 83,588 



Kaikoura), 186a- - 8y + ^u - %w = 8,665 



Wellington), 384a; - 16y + fw - |w = 36,928 



Nelson), 300^ + HO?/ + 9w - Sw = 25,525 



Hence x = 145-15 miles, y = 59-6 miles, v = 49f miles per 



minute = 4,378ft. per second (velocity of propagation), 



and the time at the origin = 8h. Imin. 20sec. a.m. The 



point K near F, five miles and a half W.S.W. of Nelson, is 



the point thus found for the epicentrum. By trial we find 



that a depth of about 5 miles for the centrum best suits the 



data. 



This agrees within the limits of errors of observation with 

 Westport, and also with Wanganui, if we take the mean of 

 the two observations (both by good observers). 



The degree of agreement is shown by the time at the origin 

 as calculated back from each place ; it should be the same, of 

 course, from whatever place we reckon. 



Time at Place of 

 Observation. 



Time at Origin below K, 



in Minutes and 



Decimals. 



Christchurch 



Kaikoura . . 

 Wellington 

 Nelson 

 Opunake . . 



Westport . . 

 Wanganui . . 

 Picton 



past 8. 



l-35min, 



1-32 



1-32 



1-33 



1-33 



l'21min. past 



1-20 



0-88 



The other places do not give a time at the origin agreeing 

 with this; but the errors are all (or very nearly all) of one 

 sign, and vary from —Imin. to — 3-96min., occurring in groups. 

 Examination of the several groups leads us to suppose that 

 there were several shocks, all nearly below K, the first deep, 

 about 25 miles down, the second higher up, and the third 

 about 5 miles below the surface. At some of the more distant 



