364: Transactions. — Geology. 



Of these times, I first rejected (c) and (d), which are not 

 stated to have been verified by New Zealand mean time ; but 

 Wellington is probably a good record, being due to Dr. Lemon 

 himself ; and the Masterton time seems to have been carefully 

 noted (by one who habitually keeps "Wellington time), though 

 not subsequently verified. 



All trials show the Upper Hutt time to be too late. Per- 

 haps the velocity of propagation was retarded locally, or, as 

 the previous tremors might suggest, the time was taken at a 

 later stage of the earthquake than elsewhere. 



White's Bay, Palmerston North, and Woodville are all 

 two to two and a half minutes at least too early, and possibly 

 refer to an earlier shock.* 



We must rely, therefore, principally on the times of the 

 nine places in (a). Comparison with the result of the normal 

 equations, indeed, shows Marton and Blenheim to be of less 

 value than the rest, but we are not warranted, prima facie, in 

 excluding them from our calculations. 



Four methods were used in finding the origin, depending 

 on the direction, time, and intensity. 



Direction. — Drawing lines in the directions given, and at 

 right angles thereto, to include cases in which the direction 

 given is that of the transverse vibrations (see Trans. N.Z. 

 Institute, vol. xxiii., p. 474), we find that we can describe a 

 circle of 15 miles radius with centre D (55 miles from Welling- 

 ton, 58 miles from Wanganui), an origin within which would 

 agree with Wanganui, Otaki, Palmerston North, Picton, Blen- 

 heim, Woodville, White's Bay, Ilavelock, and very nearly 

 with one or two others. 



Time : Method of Circles. — Using the times for Havelock, 

 Blenheim, Otaki, Wanganui, and Opunake, with a velocity of 

 11^ miles per minute, we find an epicentrum E, 49 miles from 

 Wellington, 60 miles from Wanganui. This, however, does 

 not agree with several of the other times, which are pre- 

 sumably equally good. E\ found by the same method from 

 Havelock, Otaki, Foxton, Feilding, Wanganui, Opunake, with 

 an assumed surface-velocity of 8 miles per minute, gives far 

 more satisfactory results. 



Method of Equations. — Taking Opunake as the origin of 

 co-ordinates, and the line Opunake-Havelock as the axis of x 

 (Milne's " Earthquakes," p. 206), using all the data contained 

 in (a), and forming the normal equations, we get — 



* A shock taking place at 4.28J at an origin below some point in the 

 smaller circle shown on the map, propagated with a velocity of about 

 seven miles per minute, would reach these three places at the times 

 named, and thus explain the discrepancy completely. In several of the 

 memoranda forwarded by the telegraph officers mention is made of pre- 

 vious rumbling or tremors (see especially Feilding). 



