The phrase "possible mechanism" refers to a potential or suggested way that something works or happens. It is a way to describe a theory or idea about how a process or event may occur. Full definition
This allowed them to estimate the forces acting on the slow eruption and discuss possible mechanisms for the interaction between the slow and fast phenomena. (sciencedaily.com)
The most extensive chapter of the book examines possible mechanisms of peer influence and the evidence in favor of each. (cambridge.org)
The following figure shows a simple example of how this can happen (there are also other possible mechanisms). (realclimate.org)