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Stress drop as a result of splitting, brittle and transitional faulting of rock samples in uniaxial and triaxial compression tests

Cieślik J.

Studia Geotechnica et Mechanica

2015

Vol. 37, nr 1

17--23

Rock samples can behave brittle, transitional or ductile depending on test pressure, rate of loading and temperature. Axial stiffness and its changes, relative and absolute dilatancy, yield, and fracture thresholds, residual strength are strongly pressure dependent. In this paper the stress drop as an effect of rock sample strength loss due to failure was analyzed. Uniaxial and triaxial experiments on three types of rock were performed to investigate the stress drop phenomenon. The paper first introduces short background on rock behavior and parameters defining a failure process under uniaxial and triaxial loading conditions. Stress drop data collected with experiments are analyzed and its pressure dependence phenomenon is described. Two methods for evaluation of stress drop value are presented.

Stress release during earthquake sequences

Gibowicz S.

Acta Geophysica Polonica

2004

Vol. 52, nr 3

271-299

The average stress drop and apparent stress released during 65 complex earthquake sequences from all over the world are estimated separately for foreshocks, main shocks and aftershocks. All of them but one occurred between 1977 and 1997. The Harvard CMT solutions are available for 60 main shocks, 38 foreshocks and 218 aftershocks. The stress drop is estimated using the values of seismic moment and source half duration and the scaling relations between various source parameters: seismic moment, source half duration, fault surface and fault length, taken from Harvard catalogues and other publications. The average stress drop is the highest during foreshocks (1.8 MPa), middle during main shocks (1.1 MPa) and the lowest during aftershocks (0.4 MPa). Similarly, the apparent stress, estimated from seismic moment and radiated energy taken from PDE-NEIC bulletins and other publications, is also the highest for foreshocks (0.6 MPa), middle for main shocks (0.4 MPa) and the lowest for aftershocks (0.2 MPa).

Apparent stress and stress drop from seismic events induced by mining

Gibowicz S.

Acta Geophysica Polonica

2002

Vol. 50, nr 1

35-49

Seven sets of the values of uniformly estimated apparent stress and Brune's stress drop from 987 seismic events, with moment magnitude ranging from -3.6 to 3.8, were collected from two South African gold mines, two Polish coal and two copper mines, and from the Underground Research Laboratory (URL) in Canada. They are used to examine their relations with radiated energy, seismic moment and source dimension to provide observational evidence of differences for slip-weakening as compared to velocity-weakening friction, found from elasto-dynamic source modeling of Shaw (1998). The observations from various data sets scale differently, but their pattern is not always distinctly related to the different frictions. The distribution of the apparent stress divided by the stress drop as a function of seismic moment is the most similar to the relevant distribution obtained by modeling, and it seems that both modes of friction are possible during the generation of seismic events in various mining environments.