Fracture of Rocks

Abstract

Fracture of rock specimens is discussed from the geophysical point of view on the basis of the recent investigations by various authors. First, experimental results on the ultimate strength of rocks are summarized. The strength is appreciably influenced by the following factors: distribution of applied stress, confining pressure, temperature, rate of stress application, repeat of stress application, size of specimens, etc. In quantitative investigation of relations between these factors and the strength, remarkable fluctuation of the strength should be considered. Furthermore, some characteristics of fracturing of rocks are discussed : (1) time characteristics of fracture occurrence, (2) pattern of successive occurrence of local fractures in rock specimens, (3) magnitude-frequency relation of local fractures. Lastly, based on the above-mentioned results on the rock specimens and an information derived from geodetic measurements, the fracture strength of the eartn’s crust is estimated and the stress distribution in the crust is discussed, earthquake occurrence in the region being taken into account.