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Fig. 1 a Sample with loading direction (arrows) and orientation of thin sections (x, y, z: designation of coordinates). b Deformed sample revealing shear fracture (fault) in a deformed granite sample. Note that the compressive side is to the right of the fault and the dilatational side is to the left

Figure 1 a Sample with loading direction (arrows) and orientation of thin sections (x, y, z: designation of coordinates). b Deformed sample revealing shear fracture (fault) in a deformed granite sample. Note that the compressive side is to the right of the fault and the dilatational side is to the left

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Table 1 Selected mechanical and acoustic data collected from uniaxial compression tests with acoustic emission (AE)-rate con- trol on Aue granite cores (Ag) *Critcal force is force at onset of the asymmetric fracture ‘Critical strain is strain at onset of the asymmetric fracture “Critical time is time of onset of the asymmetric fracture
Table 1 Selected mechanical and acoustic data collected from uniaxial compression tests with acoustic emission (AE)-rate con- trol on Aue granite cores (Ag) *Critcal force is force at onset of the asymmetric fracture ‘Critical strain is strain at onset of the asymmetric fracture “Critical time is time of onset of the asymmetric fracture
Table 2 Registered cracks in study areas of all samples. Below the mapped areas the total number of cracks is summarized for the fault core (C), loading (R1+R2), and extensional side (L1+L2)
Table 2 Registered cracks in study areas of all samples. Below the mapped areas the total number of cracks is summarized for the fault core (C), loading (R1+R2), and extensional side (L1+L2)
Table 3 Process zone width and fault length. W; width of opti- cally defined process zone; L fault length
Table 3 Process zone width and fault length. W; width of opti- cally defined process zone; L fault length
Fig. 3a, b Sketch of fracture process zone (PZ) width (W_) and length (S-) modified afer Zang et al. (2000). a Predicted; b real The length of the FPZ (S, length of the f breakdown zone by Cowie and Scholz 199 defined as the length between the fault tip crack with the greatest distance in front of from acoustic data (S,,;~19 mm for sample ip (Fig. 3a). In our study the length is estimated A since in thin sections we were unable to clear he fault tip (Fig. 3b). y d
Fig. 3a, b Sketch of fracture process zone (PZ) width (W_) and length (S-) modified afer Zang et al. (2000). a Predicted; b real The length of the FPZ (S, length of the f breakdown zone by Cowie and Scholz 199 defined as the length between the fault tip crack with the greatest distance in front of from acoustic data (S,,;~19 mm for sample ip (Fig. 3a). In our study the length is estimated A since in thin sections we were unable to clear he fault tip (Fig. 3b). y d
Table 4 Crack density (mm/mm7) of study areas for all samples relate with a maximum number of AEs. The AE dis- tribution on both sides of the fault is asymmetric with a steeper decrease on the dilatational side compared with the compressional side (Table 2 in Zang et al. 2000).
Table 4 Crack density (mm/mm7) of study areas for all samples relate with a maximum number of AEs. The AE dis- tribution on both sides of the fault is asymmetric with a steeper decrease on the dilatational side compared with the compressional side (Table 2 in Zang et al. 2000).
Fig. 4a-—c Distribution of crack density. a Plot of average crack density vs sample X-axis. b Plot of average crack densities paral- lel to sample Z-axis. ¢ Microcrack densities (left axes) and acoustic emission densities (right axes) in profiles nearly normal to the fault
Fig. 4a-—c Distribution of crack density. a Plot of average crack density vs sample X-axis. b Plot of average crack densities paral- lel to sample Z-axis. ¢ Microcrack densities (left axes) and acoustic emission densities (right axes) in profiles nearly normal to the fault
* Parallel to the X-axis > Parallel to the fault (Z-axis)
* Parallel to the X-axis > Parallel to the fault (Z-axis)
Table 5 Average value and standard deviation for crack density data. AD average crack density (mm!); STD standard deviation (mm'); SI-SV segments within study area C. At the fault tip (SV) crack orien- tation is more random (Fig. 5).
Table 5 Average value and standard deviation for crack density data. AD average crack density (mm!); STD standard deviation (mm'); SI-SV segments within study area C. At the fault tip (SV) crack orien- tation is more random (Fig. 5).
Fig. 5 Orientation of microfractures for the fault core (C), dila- tional (L1+L2) and compressive side (R1+R2). The rose diagrams show crack orientations for segments I-V. N Number of cracks
Fig. 5 Orientation of microfractures for the fault core (C), dila- tional (L1+L2) and compressive side (R1+R2). The rose diagrams show crack orientations for segments I-V. N Number of cracks
The tests were performed at atmospheric pressure; however, a visible step on the sample surface and fault plane solutions of detected AE demonstrate that a sig- nificant portion of fault propagation (~70% ) occurred in shear mode. High crack densities found on the com- pressive side of the fault may well be due to the spe- cific loading conditions of the experiments as sug- gested by stress modelling (Zang et al. 1998). It is hus not surprising that our observations differ from hose of Moore and Lockner (1995) who investigated samples deformed in triaxial compression. They found a higher crack density on the dilatational side of the macrofracture.
The tests were performed at atmospheric pressure; however, a visible step on the sample surface and fault plane solutions of detected AE demonstrate that a sig- nificant portion of fault propagation (~70% ) occurred in shear mode. High crack densities found on the com- pressive side of the fault may well be due to the spe- cific loading conditions of the experiments as sug- gested by stress modelling (Zang et al. 1998). It is hus not surprising that our observations differ from hose of Moore and Lockner (1995) who investigated samples deformed in triaxial compression. They found a higher crack density on the dilatational side of the macrofracture.
Fig. 7 a Plot of average crack width parallel to X-axis. b Plot of average crack width for the profiles parallel to the fault (Z-axis). c Plots of crack numbers vs crack lengths for the red Aue gran- ite samples (Ag18r, Ag51r, and Ag53r)
Fig. 7 a Plot of average crack width parallel to X-axis. b Plot of average crack width for the profiles parallel to the fault (Z-axis). c Plots of crack numbers vs crack lengths for the red Aue gran- ite samples (Ag18r, Ag51r, and Ag53r)
Agr-granite samples, the plot suggests a linear correla- tion between displacement and fault lengths.
Agr-granite samples, the plot suggests a linear correla- tion between displacement and fault lengths.
Fig. 9a, b Plot of process zone width vs fault length. a Data from this study; b data from this study compared with data from field studies Fig. 8 Deviation from average crack density (mm/mm/7) for 166 study areas. Plus and minus difference from sample average
Fig. 9a, b Plot of process zone width vs fault length. a Data from this study; b data from this study compared with data from field studies Fig. 8 Deviation from average crack density (mm/mm/7) for 166 study areas. Plus and minus difference from sample average
Table 6 Crack-density data and fracture surface energy. pc average crack density; V- cumulative volume of the optically defined FPZ; A,,, total area of macrofracture; Gy, fracture ener- gy; G, total strain energy
Table 6 Crack-density data and fracture surface energy. pc average crack density; V- cumulative volume of the optically defined FPZ; A,,, total area of macrofracture; Gy, fracture ener- gy; G, total strain energy
Fig. 11 Fault trace (geometry, fault width) in relation to fault propagation velocity (Zang et al. 2000). The resulting velocities range from 2 to 130 um/s in acoustic emission rate-controlled tests
Fig. 11 Fault trace (geometry, fault width) in relation to fault propagation velocity (Zang et al. 2000). The resulting velocities range from 2 to 130 um/s in acoustic emission rate-controlled tests
Related topics:
Earth SciencesGeologyFracture Propagation
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