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Four Granites in the Lab: Acoustic Emission During the Uniaxial Loading

Description: 

Laboratory loading experiments on rock samples are proxies of earthquakes in nature, and acoustic emission (AE) is an eye into the rock to view its fracturing. Obviously the texture and grain size are the crucial parameters ruling the properties of a rock. We analyzed four different granites in the uniaxial loading to observe the way of their fracturing in terms of (i) the time sequence of the AE initiation and its clustering in time and space, and (ii) of the retrieval of the mode of the fracturing. The shear-tensile crack (STC) source model is advantageously used as a robust inversion tool. Concerning (i), from the seismicity distribution in space and time we evaluated the correlation integrals, and from them the fractal dimensions in space and time. While the temporal fractal dimension seems to be independent of the granite type, the spatial fractal dimension decreases slightly on the line from the fine-grain granite to that one with the largest grain size. It means that in the latter case the AE foci are clustered more than in the former one. Within the study (ii), we performed a detailed analysis of the errors of the retrieved mechanisms in terms of constructing the confidence regions related both to (a) the geometry/orientation of the mechanism and (b) its decomposition into shear vs. non-shear components. In this way we sorted the seismicity into shear events (S), shear-tensile (ST) and tensile events (T) and analyzed their occurrence and orientation changes in the course of the experiment. A simplistic prior idea about prevalence of shear fracturing in materials with grains of large size seems to be not supported.

Session: Earthquake Source Parameters: Theory, Observations and Interpretations

Type: Oral

Date: 4/18/2023

Presentation Time: 11:00 AM (local time)

Presenting Author: Zuzana Jechumtálová

Student Presenter: No

Invited Presentation: 

Authors