f Stress memory effects in rock - Possibilities to assess in-situ rock stress magnitudes from cores

Acoustic Emissions (AE) are transient elastic waves caused by the development of damage (due to, e.g., microcrack growth and pore collapse) in rocks under mechanical load. AE can be used to study stressmemory effects in rock. This is illustrated by the following experimental observation. When a rock sample is loaded uniaxially for the first time beyond the elastic limit, it will start producing AE. That same sample, however, will not produce any AE upon re-loading in the same direction until the previous maximum stress level is exceeded. In other words, the stress level at the onset of AE during re-loading is the maximum stress level that was applied the first time. This phenomenon is known as the Kaiser effect.