We use previously published laboratory friction experiments on a natural fault zone sample from the Nankai Trough subduction zone offshore Japan. The sample is composed of ~50% clay minerals and comes from within a major splay fault (the "megasplay"). Using this sample, we conducted a series of experiments at effective normal stresses of 2-18 MPa, with a single velocity-step from 0.1 to 10 μm/s in each experiment. The experiments were conducted at effective normal stresses of 2-18 MPa, with a single velocity-step from 0.1 to 10 μm/s in each experiment. We performed new analyses, modeling the velocity steps with both a 1-state variable and 2-state variable friction law using RSFit3000 and usethe sum of squared residuals to quantify goodness of fit.