Magnetic, seismic and mechanical properties of porphyritic meta-rhyolites — The effect of microscopic foliation on rock strength and P-wave velocity in drill cores

Seismic velocity and rock strength in drill cores have previously been shown to vary depending on the angle between the measuring direction and the macroscopic foliation plane, but very little research has been performed on samples with a microscopic foliation. In this study, we use the anisotropy of magnetic susceptibility (AMS) to identify a foliation in what has been assumed to be isotropic rhyolites. We then use scatterplots and simple linear regression analysis to identify and quantify the relationships between AMS, diametrical P-wave velocity and point load (PL) strength in the ferromagnetic samples. Our study suggests that the PL strength increases with 56% when the angle between the foliation plane and the measuring direction is increased from 14° (close to the foliation plane) to 65°. Such a high change in rock strength with direction, in rocks with no macroscopic foliation, could have serious implication e.g. in rock mechanical modeling, and AMS can thus be used as a tool predict fracturing.

► Identification of microscopic foliation in meta-rhyolites with magnetic anisotropy
► Strong correlation of petrophysical and rock mechanical properties
► Point load strongly dependent on the angle to the foliation plane
► Predictive equations for point load and P-wave velocity.