Abstract Frictional slip behavior in fault zones can be analyzed with friction laws using 1 or 2 state variables, but the physical meaning and applicability of the 2‐state variable form of the law remain unclear. Here, we re‐analyze friction experiments by Roesner et al. (2022, https://doi.org/10.1186/s40623‐022‐01728‐w) using a natural sample from the megasplay fault in the Nankai subduction zone offshore Japan. At low effective normal stress, the 2‐state variable law provides a superior fit to velocity‐weakening friction data, whereas the 1‐state variable law is appropriate for velocity‐strengthening data at higher stress. This transition coincides with a significant reduction of the parameter b2, suggesting that a specific physical mechanism responsible for velocity weakening is active at low stresses. This mechanism is likely associated with a localized microstructure in a gouge with high relative stiffness and high porosity.