Mechanical strength of Anhydrite and its Role in the Seismicity of the Duke River Fault, Yukon Territory Sampaleanu, Christian
Anhydrite rich fault zones are known to act as zones of weakness and the source of earthquakes in seismically active areas. One of the best known examples is the Apennine Mountains in Italy, which contain neo-tectonic extensional faults hosted in carbonate and evaporite sequences. For this study, anhydrite from the Duke River fault in the Yukon was sampled and triaxial stress tests were conducted to determine the mechanical strength of the anhydrite. Both pure shear experiments and friction experiments were performed. These tests show that anhydrite will begin to undergo brittle-ductile deformation at confining pressures as low as 25 MPa. At atmospheric conditions, anhydrite behaves elastically until brittle failure results in the formation of a shear fracture with associated stress drop. At confining pressures greater than 75 MPa, anhydrite will deform by cataclastic flow, and no longer produce a stress drop. The data indicate that the anhydrite-rich locations in the Duke River fault likely could not be responsible for a stress drop and therefore it is unlikely that the anhydrite-rich portions of the Duke River Fault are the sources of the seismicity. It is proposed that high fluid pressure would be required to promote brittle failure that could cause the seismicity.
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