Refer to figure.
In the same way that separated airflow prior to a low speed stall can cause airframe buffet, shock induced separation (shock stall) at high speed can also cause buffeting.

Aerodynamic buffet is a valuable stall warning, but it can damage the aircraft structure. Because of the higher dynamic pressure when an aircraft is operating in the transonic speed region, any shock induced buffet will have a greater potential for severe airframe damage.

High speed buffet must be completely avoided. The aircraft must therefore be operated in such a manner that a (safety) margin exists before aerodynamic buffet will occur.

If the variables which affect both high speed and low speed stall are considered it will be possible to identify the conditions under which buffeting will occur and a chart can be drawn to show all the factors involved.

This is called a ‘Buffet Onset’ chart which is used by flight crews to ensure their aircraft is always operated with a specified minimum buffet margin.

For any given combination of mass, center of gravity position and airspeed, the maximum operating altitude is that altitude at which a normal positive acceleration increment of 0.3 g, without exceeding the buffet onset boundary, is possible.

Note: Flying in turbulent conditions may cause sudden changes in speed and load factor. Looking at the buffet margin graph attached, we can conclude that both speed/mach variations and changes in load factor may bring the aircraft closer to one of the buffet margins.