Coherent Identifier About this item: 20.500.12592/k4br74

Memoirs of the Geological Survey of India Report on the Great Earthquake of 12th June 1897




2. The shape of the orbit in which the particles of water travel changes gradually as the wave progresses, as may be seen in the gradually changing form of the waves as-they travel outwards, but the change is slow and, for any given spot, the tracks in which all the particles of water move may be iegarded as similar, and the nature of the wave motion can be defined by the shape of the track follow [...] The movement is in fact just like that of the bob of a pendulum, assuming the direction of travel of the wave to be that of the swing of the pendulum. [...] Returning to the diagram fig ii, the distance from o to 4 is the amplitude of the wave, or the extreme distance which the wave-particle reaches from its normal position ; 4 to 12 is the double amplitude or range of motion of the particle, and the time taken by the wave-particle in travelling from o out to 4 And back through 12 to o is the period of the wave. [...] Whatever may be the nature of the laws which govern the movement of the wave-particle in these surface undulations it is hardly possible that they can be the same in the case of waves which differ so much in size and rate of move- ment as the two forms of surface wave referred to in the preceding paragraph This conclusion appears to be supported by the absence of any passage from the one to the ot [...] In the case of earthquake waves in the region where the shock is severe enough to be felt, nothing of the sort has been recognised and nothing of the sort is to be expected, seeing how heterogeneous are the materials of which the outer crust of the earth is composed.


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