We used a mechanics conceptual model to provide another perspective to understand the mechanical environment of the San Andreas Fault(SAF),and a possible mechanism that the principal stress state in the SAF is not only affected by remote tectonic stress but also by Poisson’s ratio.For a strike-slip fault like the SAF,we found that in the fault zone with Poisson’s ratio of[0.25,effective friction coefficient and the stress ratio(minimum principal stress/maximum principal stress)are less than 0.1and 0.8–1.0,respectively,corresponding to remote tectonic stress ratio of 0.36–1.0,and that the higher the Poisson’s ratio,the greater the principal stress rotates.For hydrostatic pore pressure and a received tectonic stress ratio of 0.5around the SAF,the model predicts that the SAF has a very high Poisson’s ratio(*0.45),which accommodates extremely low effective friction coefficient(0.09)and large stress ratio(0.84)or smaller shear stress(17 MPa).
