Small Sand Craters of Seismic Origin

Abstract

THE small sand craters of seismic origin, described by Dr. Sheppard in NATURE of December 30 (p. 1006), as examples of unusual structures, are common results of severe earthquakes in alluvial regions. The formation of such vents and their related fissures was first explained by R. Mallet and T. Oldham in the case of the Cachar earthquake of January 10, 1869¹, and their theory was adopted later by R. D. Oldham in his description of the numerous and widely spread occurrences caused by the Great Indian earthquake of June 12, 1897². Briefly, this theory postulates a certain amount of vertical movement from below, resulting in the transmission of the wave motion through layers of loose, oozy sand into the overlying, impervious and harder layers of the surface alluvium. The inertia of the latter is believed to cause a compression of the watery sub-stratum and the expulsion of part of its contents through simultaneously formed cracks above, usually as a geyser-like flow. The spurting which reliable eyewitnesses state takes place on these occasions, the return of the water when quiescence is attained and the formation of the craters with their scored sides, are all accounted for satisfactorily by this theory.