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Acoustic Emission in a Laboratory: Mechanism of Microearthquakes Using Alternative Source Models
Author(s) -
Petružálek M.,
Jechumtálová Z.,
Kolář P.,
Adamová P.,
Svitek T.,
Šílený J.,
Lokajíček T.
Publication year - 2018
Publication title -
journal of geophysical research: solid earth
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.983
H-Index - 232
eISSN - 2169-9356
pISSN - 2169-9313
DOI - 10.1029/2017jb015393
Subject(s) - acoustic emission , moment tensor , shear (geology) , ultimate tensile strength , source model , materials science , slip (aerodynamics) , geology , acoustics , deformation (meteorology) , physics , composite material , computational physics , thermodynamics
Here a shear‐tensile crack (STC) model is presented as suitable for acoustic emission (AE) events. Experimental data were obtained from a uniaxial compression test performed on a Westerly Granite specimen using a 14‐channel AE monitoring system. The advantages of the STC versus a traditional MT (moment tensor) approach are as follows: (i) it is a physical source, contrary to the MT, since the STC describes the straight and simple fracture modes anticipated inside a loaded sample, namely, the shear slip and both the opening and closing tensile cracks; and (ii) it is simpler because it is described by fewer parameters (five instead of the six required for an unconstrained MT), which is essential for solving the inverse problem. The presented STC procedure was tested on 38 AE events selected over a range of 50–98% for the uniaxial compressive strength. As compared to the MT model, the STC model displayed a similar fit for input data while providing far smaller confidence regions. The results indicate a more certain determination for the mechanism of orientation and improved reliability for the decomposition components. In addition, use of STC model allowed better distinction between tension and shear type for AE events, which may be crucial for recognizing an approaching failure. For our experiment, application of the STC model proved to be useful for recognizing the threshold of unstable microcracking and indicative for determining the failure plain orientation.