Laboratory Modeling of Aftershock Sequences: Stress Dependences of the Omori and Gutenberg–Richter Parametersстатья
Информация о цитировании статьи получена из
Web of Science,
Scopus
Статья опубликована в журнале из списка Web of Science и/или Scopus
Дата последнего поиска статьи во внешних источниках: 26 июня 2019 г.
Аннотация:Laboratory experiments on studying the aftershock regime are carried out on sandstone specimens atdifferent levels of axial loading and uniform compression and at constant pore pressure. The aftershock sequencesare modeled by the scenario of stepwise increasing axial loading of a specimen with strain control, which ensuresthe regular generation of aftershock sequences. The experiments are conducted on intact specimens and on thosewith preliminarily formed shear macrofractures simulating natural faults. The multichannel recording of the signalsof acoustic emission (AE) during the experiments allowed locating the AE sources. Several types of the dependenceof the parameters of relaxation of the acoustic activity—parameters p and c of the modified Omori law and theGutenberg–Richter b-value—on the level of acting stresses are revealed. The b-value decreases with the growth ofaxial stresses at all levels of uniform compression. In the case of a fracture on the preexisting fault, the Omori relaxationparameter p increases with the growth of axial stresses; parameter c—the time delay before the onset of relaxation—decreases with the growth of axial stresses and increases with the rise of the level of uniform compression.In the case of a fracture of an undamaged specimen, parameter p remains unchanged with the growth of axialstresses, whereas parameter c increases slightly. Parameter variations in the case of a complex stress state with bothvarying deviatoric (differential stresses) and spherical parts (effective pressure) of the stress tensor take on a unifiedform when expressed in terms of Coulomb stresses. It is hypothesized that the time delay of the relaxation of theaftershock activity is determined by the kinetics of a fracture in accordance with the kinetic concept of strength insolids. This hypothesis is supported by the exponential dependences of parameter c on stresses and the effectivestrength of the medium which are revealed in the experiments. Under this hypothesis, based on Zhurkov’s formulafor the durability of materials, it is possible to unify the dependences of parameter c on the Coulomb stresses at differenteffective strength values. The obtained parameter estimates for the dependence of c on strength and stressessuggest that the c value is determined by the difference of the strength and the acting stresses, thus indicating howfar the stress state of the medium is from critically corresponding to the ultimate strength.