" Vol. I. No. 6, N.Z. JOURNAL OF SCIENC2 (New Issue) NOV., 1891. 



EARTHQUAKES IN NEW ZEALAND— WHAT 



AND HOW TO OBSERVE. 



BY GEORGE HOGBEX, Jf.A., TIMAR". 



It may be necessary to answer a preliminary question, ' W ky 

 should we observe earthquakes at all "? ' ; for there are some people 

 who consider that by calling attention to the subject we shall be in 

 danger of gaining for New Zealand an unenviable notoriety. As a 

 matter of fact, however, a very limited examination of the earthquake- 

 history of the colony shows that, if indeed the objection be seriously 

 urged, no fear need be entertained on that ground. Out of nearly 

 800 earthquakes recorded in New Zealand only two or three can be 

 called severe* — namely, those of October, 1848, January, 1855, and 

 perhaps one other, (about which little definite information can be 

 obtained, but which seems to have had marked effects in the district 

 between Mts. Tarawera and Edgcumbe in the year 1836). A few 

 more come under the head of sharp, and all the rest — the vast 

 majority — are certainly not entitled to a moie serious adjective than 

 slight. No earthquake in New Zealand, at least in historic times, has 

 been at all comparable with the terremotos or destructive earthquakes 

 of South America. The minds of the timid may therefore be re- 

 assured by the thought that the experience of the past does not lead 

 us to expect greater danger from earthquakes in New Zealand than 

 in England. 



Besides removing this objection we may, perhaps, be expected to 

 give some positive reason why earthquakes should be observed. The 

 object is mainly a scientific one, though, as in many other inquiries 

 purely scientific at the outset, practical conclusions and results may 

 follow. Seismology is merely one branch of a larger subject, the 

 Physics of the earth's crust, a complete study of which involves 

 questions connected with the figure of the earth, the nature of its 

 interior — whether liquid or solid, or partly liquid and partly solid, or 

 solid by reason of the pressure though liquid in potentiality; its 

 temperature, and rate and mode of cooling — by conduction if solid or 

 viscid, by convection if liquid; the nature of the internal movements, 

 if any ; the consequent nature and causes of the compressions and 

 movements that take jnace near the surface. The most important 

 evidence towards forming probable theories about these matters is 

 yielded by the phenomena connected with volcanic eruptions, and 

 wdth the various earth-movements — earthquakes, earth-tremors, earth- 

 tides or pulsations, and those larger and slower movements revealed 

 in the elevation or depression of the land. Other effects of the forces 



* It would take too long to attempt a definition of the terms severe, sharp, slight. 

 Their use is not free from vagueness, but they give a convenient classification of 

 shocks, based upon such easily observed phenomena as the stopping of clocks, the 

 falling of bottles from shelves, injury to chimneys and walls of buildings, and so on- - 

 the appropriateness of the particular adjective depending also upon the more or less 

 general occurrence of these events in any given district. 



