EARTHQUAKE SHOCKS.

New Zealand Herald, Volume LXIII, Issue 19412, 21 August 1926, Page 11

EARTHQUAKE SHOCKS.

RESISTANCE OF BUILDINGS. THE PERIOD OF VIBRATION. facts; and suggestions: {by telegraph, —own correspondent. ] ' WELLINGTON. Friday. In a lecture on buildings in earthquakes Dr. C. E. Adams, the Government seismologist, described in detail what takes place when a earthquake occurs. Series of waves are transmitted from tljo place of origin, longitudinal waves travelling roughly at fonr ! miles a second and transverse' waves at two miles a second. An earthquake was a continuous oscillation, and not just an isolated shock. There was sometimes "a limited vertical yibra--1 ion, but it was an erroneous idea that damage was caused to buildings by an upward jerk followed by a settling down 61 the {structure. The vertical component of an earthquake was always considerably less than the horizontal. Every, building had. its inherent vibration period. The strength of a building as regards ability to 1 resist earthquake shocks depended entirely upon its vibration period. It was now universally recognised that it was the synchronisation of tho vibration .period of the shock with tie vibra-tion--period of the building which caused the daruago. Unfortunately tho vibration period of many structures was: between half a second and two seconds arid this corresponded to the average period of the earth's, oscillation during tho earthquake. Hence in modern buildings erected in earthquake zones efforts wore made to make structures with a vibration period either more or less than these figures. It was simply inviting trouble, commented Dr. Adams, to erect structures of materials with different vibratory periods. The more a building was "ship built, M • all Of .one) material, the hotter its,-chance of surviving an upheaval of the earth. This was demonstrated in tho overthrow of chimneys during an earthquako. Under the influence of a violent horizontal vibratory motion caused 'by tho earthquako a wooden house vibrated with a period . of its. own ; and the - brick ciiimney also vibrated with'a period of its own.' Tho moment was bound to come ! when these vibration periods opposed each other 'and thfen - tho chimney broke off at : its junction with .the roof; Tho lecturer said it seemed to him a feasible idea in these days >; to abolish chimneys altogether. Electricity and' gas were tending to mako them •superfluous. The necessary'draught : for ventilation and other purposes being obtainable by'means of fans.

Dr. Adams .pointed out that tho danger spot in a high building/was about twothirds of the way up, whereas in , ft stumpy building tho effect of tiu ; . earthquake shock would bo most severely felt near tho bottom. Adequate exits from public buildings woro very necessary in case of earthquakes.

Wellington was taking a stop in. tho right direction >by providing several small reperroini quake the main water supply was liable jto interruption* 'greatly .adding to tho danger of< fire/ }TJ». proyisiqn:; t of. Bevor.al small reservoirs, 'helped -'to ■ feUtwiato', this danger. He also advocated .tho holding of municipal conferences to. determinate course of action to be taken /after . a serious earthquake. 1 : ■ ' ,:> s •: ■ ■