Strain rate and temperature dependence of Omori law scaling constants of AE data: Implications for earthquake foreshock-aftershock sequences

Abstract

Little is known about the temperature and strain rate dependence of acoustic emission AE activity (AE). Hence, we carried out a preliminary series of flow-through triaxial compression tests on porous sandstones at different temperatures and strain rates. The AE data exhibits clear foreshock and aftershock sequences with respect to the dynamic failure of the test specimen. Significant AE activity starts less than 5 min before sample failure irrespective of the strain rate. The increase in the AE event rate is steeper and the foreshock exponent p′' is smaller in the slow strain rate tests. It could be the reason why there are no easily recognisable foreshock sequences for most individual earthquakes. The aftershock decay parameter p is a linear function of test temperature as it has also been inferred for natural seismicity. The seismic b-value decreases systematically with increasing deformation rate suggesting a greater proportion of small cracks in the slow strain rate tests. Hence, the AE activity is a function of both strain rate and temperature. Copyright 2004 by the American Geophysical Union.