. The geography of New Zealand. Historical, physical, political, and commercial . ing table shows the transit-velocities ofthe chief waves of the four earthquakes just referredto in kilometers per second:—? Earthquake a waves. e waves. h waves, Guatemala 15-6 3-2 2-1 Tonga 13-0 3-3 Cheviot 12-4 3-5 2-3 East Coast 12-5 3-5 The high transit-speed of the a waves or pre-liminary tremors can be accounted for only on theassumptions, (1) that the vibrations originated inrocks under a maximum strain (it will be remarked 238 GEOGRAPHY OP NEW ZEALAND that the speed is greatest for the earthquake
. The geography of New Zealand. Historical, physical, political, and commercial . ing table shows the transit-velocities ofthe chief waves of the four earthquakes just referredto in kilometers per second:—? Earthquake a waves. e waves. h waves, Guatemala 15-6 3-2 2-1 Tonga 13-0 3-3 Cheviot 12-4 3-5 2-3 East Coast 12-5 3-5 The high transit-speed of the a waves or pre-liminary tremors can be accounted for only on theassumptions, (1) that the vibrations originated inrocks under a maximum strain (it will be remarked 238 GEOGRAPHY OP NEW ZEALAND that the speed is greatest for the earthquake ofgreatest intensity) ; (2) that their path through theearths crust was the path of maximum velocity, andtherefore through the rocks of highest rigidity andelasticity. The velocities of the e waves and Ji waves forvarious large earthquakes seem to vary very little,the average being and kilometers per secondrespectively. Now from theory, based upon, theexperimental determinations of the rigidity, elas-ticity, and density of various rocks, the speed of *1 Scale 59 m m. = i Uout* Fig. 9 : East Coast earthquake on 9th August, 1904. (VNenington reccwd.) large normal or longitudinal vibrations through suchrocks as hard granite is estimated to be between km. per second, and the speed of transversewaves two-thirds of that of normal waves proceedingfrom the same origin at the same time and along thesame path. It is therefore highly probable that e and]i on the seismograms (of which those given arefair specimens) represent the chief normal and trans-verse waves, due, as we have seen, respectively toelasticity of volume and elasticity of , if the rocks were subjected to greatpressure, as must be the case at a few miles EARTHQUAKES AND OTHER EARTH MOVEMENTS 239 below the surface, the strain would be at a maximumjust before yielding, and the consequent vibrations(«) would be small and rapid; as the rocks yieldedto the strain, and were compressed,
Size: 2742px × 912px
Photo credit: © Reading Room 2020 / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookauthorgregoryj, bookcentury1900, bookdecade1900, bookyear1905
