Hogben. — On the East Coast Earthquake. 423 



The best time-observations in New Zealand were— 



Napier 



Wellington ... 

 Nelson 

 Christchurch 

 Wanganui ... 



These, by the method of circles or the method of equa- 

 tions, gave the position of the origin as 42° 23^' S. lat., 178° 

 58 r E. long. — that is, the epicentral area was situated about 

 a point 215 miles S.E. by S. from Napier, and 227 miles 

 E.S.E. from Wellington. The depth of the origin is un- 

 certain, but it was probably about 15 miles (24 kilometers), or 

 a very little less. 



The transit-velocity of the large waves (longitudinal waves) 

 was 129-6 miles per minute, or 3-48 kilom. per second. 



The transit-velocity of the preliminary tremors (rapid fine 

 w r aves), as determined from the seismographic records, was 

 about 478 miles per minute, or 12*8 kilom. per second. The 

 speed of the transverse waves, similarly determined, was 

 2-2 kilom. per second. 



The averages of the corresponding numbers for nineteen 

 large earthquakes, as calculated by Professor Omori and Mr. 

 Imamura, of the Hongo Observatory, Tokyo, are — 



Kilom. per Second. 

 Preliminary tremors, velocity (Vi, Imamura) 13 - 2 

 Large waves (V 5 ) ... ... ... 3-3 



Transverse waves (V 8 ) ... ... ... 2-1 



{Earthquake, Investigation Committee of Japan.] 



The theoretical value of V 5 for hard granite is 3-95 kilom. 

 per second : the value 348 kilom. per second would agree 

 with a hypothesis that these waves passed for two-fifths of 

 their path through granite, and for the other three-fifths 

 through some such rock as limestone. 



The seismogram taken at Wellington shows a very slight 

 tilting towards the west, probably evidence of slipping or 

 accelerated folding of the underlying rocks. 



The main earthquake was preceded by slight shocks in 

 July and August, and was followed by after-shocks (twenty or 

 more) until October. 



The origins of these and other earthquakes, notably that of 

 1863 already mentioned, and that of the 9th March, 1890, 

 seem to be situated in or near a strip or region of the earth's 

 crust shown on the map as EE (Plate XLIX.), which is parallel 



