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In this work, we successfully identified seismic events (observations of earthquakes) in seismograms using a Convolutional Neural Network (CNN). In accordance with past (analogue) seismogram interpretations, we did not treat digital seismograms as a time series, as per the general method, but, rather, converted them into time snaps of continuous data flow. Multichannel seismograms were represented with a time-frequency domain in the form of multilayer images, with each signal channel forming one image layer. Images were then exposed to CNN (composed of three convolutional blocks whose architecture design was justified using Bayesian optimization). To improve reliability, we evaluated the posterior type function (PTP) as a combination of the probabilities of all of the considered classes of signal types (five in our case) which increased robustness of the identification. For data, we used records of acoustic emission (AE) events. The events were generated during laboratory loading experiments originally performed to study material/rock properties. As known, AE events may be studied in the same manner as natural earthquakes and treated in other ways as laboratory earthquake models. AE events are less complex compared to natural earthquakes where many of the physical parameters are known or may be controlled. Based on our results, we concluded that the successful identification of AE events is a necessary step prior to applying the proposed methodology for identifying natural earthquakes in seismograms. [ABSTRACT FROM AUTHOR]

Volumetric studies of mica spatial distribution inside samples of Westerly and Czech granites (Mrakotin, Liberec, and Brno syenite) were performed using a neutron tomography method. A significant difference in the neutron attenuation coefficients of mica and other rock-forming minerals of the granites studied yielded a large neutron radiography contrast and, as a result, allowed us to perform a detailed analysis of three-dimension structural data based on the neutron tomography reconstruction procedure. The morphology and spatial distribution of the mica phase within studied granites were obtained. Tomography data were compared to results provided by other experimental methods commonly used in rock mechanics research such as optical and electron microscopy, as well as ultrasonic shear-wave measurements. The benefits and limitations for application of the neutron tomography method for studies of granite like rocks are discussed. [ABSTRACT FROM AUTHOR]

Rock massifs traditionally used for the construction of foundations, tunnels or as a source of crushed stone, frequently contain compositionally (texturally, mineralogically, geochemically) contrasting inclusions – xenoliths. The presence of xenoliths is a commonly overlooked fact which may, however, significantly affect the total strength of the massifs. The most frequent xenoliths in igneous massifs are mafic microgranular enclaves occurring as ellipsoidal inclusions with the size varying from centimetre to metre scales in the host rocks. Our pilot experimental study brings a complex assessment of strength properties (e.g., rebound hardness, uniaxial compressive strength, rock tensile strength) of multicomponent geomaterials, i.e., host-rocks and their enclaves, sampled both from quartz-rich (granitoid) and quartz-poor (syenitoid) massifs. [ABSTRACT FROM AUTHOR]

Migmatite from the Skalka region (Czech Republic) was chosen as an experimental rock material. It has a macroscopically visible plane-parallel structure (foliation). The foliation was caused mainly by biotite grain arrangement. Four cylindrical specimens of migmatite with sub-horizontal, sub-vertical and oblique foliation were uniaxially loaded up to failure. A network of 8 broadband sensors was employed for acoustic emission monitoring and ultrasonic sounding. A grid search method with an anisotropic velocity model was used for AE hypocenter localization. The source types of successfully localized events were determined from the average first arrival amplitude. Structural anisotropy of the tested rock material caused the anisotropy of its mechanical properties (peak strength, Young's modulus) as well as a different fracturing in dependence on the angle between the axial stress and the foliation plane. The combination of tension and shear microcracking together with sliding in biotite basal planes was found to control the failure of specimens with sub-horizontal foliation. Shearing and sliding were dominant in the failure of specimens with oblique foliation. With greater dip of foliation, the role of sliding increased at the expense of shearing. Due to the favorably oriented system of microcracks already present, the shearing and splitting was at the same level during fracturing of specimens with sub-vertical foliation before nucleation began. [ABSTRACT FROM AUTHOR]