ah ha! I think. — the characteristics of the 3 waves that come before stick-slip (which part of the process of going from static friction to kinetic friction)
I saw these referenced in a few other papers but this is so far the most detailed.
“The slip pulse, characterized by a sharp stress front, propagates in the same direction as the Schallamach wave. In contrast, the separation pulse, involving local interface detachment and resembling a tensile neck, travels in exactly the opposite direction. A change in the stick-slip mode from the separation to the slip pulse is effected simply by increasing the normal force. Taken together, the three waves constitute all possible stick-slip modes in low-velocity sliding.”