James P. Evans, Kelly K. Bradbury

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We aim to characterize fault-structure-related rocks via correlation between the various geophysical characteristics of samples retrieved from the southern San Andreas Fault (SSAF) near the Mecca Hills region in Southern California. Samples from this area were retrieved from the San Andreas Fault Observatory at Depth (SAFOD) near Parkfield, California at a depth of approximately 3km. Core samples of various lithologies were gathered from the borehole and analyzed using various geophysical methods. Emphasis was placed in possible correlations and relationships between varying lithologies and calculated values of unconfined compressional strength (UCS) and cohesion. Using retrieved data from the samples, as well as experimental data from previous experimental laboratory gathered data, values for strength and cohesion were calculated to demonstrate potential rock characteristics at in situ conditions. The geophysical and geomechanical values retrieved from these calculations were then correlated to damage zone dimensions via computational analysis in MATLAB. We also found frictional coefficients and shear strength and their empirical relationship with cohesion and UCS in order to demonstrate fundamental properties in rock strength.

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