Fig. 11

Principal stress axes analysis for foreshocks (left) and aftershocks (right) by method of Michael (1984) with uncertainty estimate coded by Vavryčuk (2014); panels a, b show confidence limits of principal stress axes visualized by 500 randomly perturbed pure shear solutions by the approach of Vavryčuk (2014) for foreshocks and aftershocks, respectively. In panels c, d are histograms of their respective shape ratios defined as \( { = }\frac{{\sigma_{1} - \sigma_{2} }}{{\sigma_{1} - \sigma_{3} }} \). Note that the relatively low shape ratios imply \( \sigma_{1} \approx \sigma_{2} \)