Abstract
THE character of earthquakes, that is, of the disturbance which can be felt and causes damage, has long been established as a form of elastic wave motion, originated by some sudden disturbance in the substance of the earth. In some cases, such as the Japanese earthquake of 1891 or the Californian of 1906, the earthquake was accompanied by visible fractures and displacements of the solid rock, and where these have been observed it has also been noticed that the violence of the disturbance reached its maximum close by, and became less as the distance from the fracture increased. From this it is evident that, in such cases at least, the earthquake originated from the jar caused by sudden rupture of the rocks, and the fault, or fracture, may be regarded as the cause of the disturbance to which the earthquake was due. In many other cases, where no actual faulting or fracture is visible at the surface, and especially in earthquakes of moderate intensity and extent, a study of the observations makes it very probable that the immediate cause of the disturbance was a fresh movement along an old fault, or the formation of a new one, and so may be found in many text-books the statement, put forward and elaborated, that faults are the cause of those earthquakes classed as tectonic. Thus it might seem that the cause of earthquakes had been explained, but this is only the beginning of the story, for we need to know what causes the fracture which gives rise to the earthquake.
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OLDHAM, R. The Character and Cause of Earthquakes. Nature 111, 432–434 (1923). https://doi.org/10.1038/111432a0
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DOI: https://doi.org/10.1038/111432a0