EARTH MOVEMENTS.

Grey River Argus, 8 December 1928, Page 2 (Supplement)

EARTH MOVEMENTS.

The number of earth tremors and small earthquakes has been calculated to be about 30.000 per year, but there

are only a limited number of shock that do great material damage and take a heavy toll of human life. It is not always however, the earthquake that wreaks the most destruction that

is the greatest in intensity, for one that occurs among crowded human habitations will always, be more marked than one with a centre, say, in Siberia or the plains of Mexico. Even the Japanese earthquake of 1923, with its roll of killed and injured by nearly 100,(100 measured by the maximum intensity of shock and •the area affect-

ed, ranks as a great earthquake, but not by a,ny means among the greatest on record, though it certainly is the most destructive known. Careful in-

vestigations have enabled seismologists to plot the areas where great earthquakes occur, and the west coast of North and South America has at time? produced grim and alarming evidence of enormous destruction of life and jjroperty by earthquake shocks of great

magnitude. The great San Francisci shock in 1906 i s still fresh in the memory o f many, and there are records of a great earthquake in Chile, nearly a hundred years ago. when th‘e country for a thousand miles was af fected by a shock that materially al tered the coast-line and did immense damage. There is no completely satis factory theory of the origin of earthquakes, none of which is necessary aud sufficient. But it is generally accepted that in many case. 3 and probably in all of a certain type, earth strains are set up resulting in distortion ami fracture of the outlying rock near the surface. If has been pointed out by leading seismologist> that all the great earthquake areas are found where high mountains and great ocean depths are neighbours, and the geographical distribution of earthquakes frequently supports this view.. The Andes, for example, average probably 14,000 feet in height, aud only a narrow roastline separates them from a corresponding depth of th“ ocean bed at no great distance seaward.