Unless I missed it in the Advanced rules, there does not seem to be a crushing mechanic?

Is that usually handled as a continuous Charge attack of a certain intensity? (which could be a valid method)

If so, is that official (book and page number, please), or is that just a common houserule?

If not, where does it mention a crushing mechanic? (book and page number, please.)

I can't think of one, though I would probably not make it based off of a charge since I'm not sure movement speed or Endurance is relevant unless you intend to make some sort of getting run over move. I think I would do a Strength intensity feat against the strength of the attack, with a success negating the damage and a failure dealing the damage again and beating the needed result by one color ending the attack.

Do you mean crushing as in a machine crushing someone or a continually applied crushing effect?

Grappling resolves to Crushing.

Crushing from a machine is an effect so it would be a readied attack or an effect to avoid with Agility or resist with Strength, surely.

The Real Time Traveller (R) has it, i think. Grappling damage.

I would agree with The Real Time Traveller. A continuously applied Strength of the machine applied every round to everything within the machine.