I think I'd say it is two "triggers" if by that you mean "conditions for selective effect".
Selection 1: Only bipeds
Selection 2: Only moving superhumanly fast
I'd make it a ward with those selections, and an attached evocation "landmine". Nothing whatsoever happens to anyone that doesn't fulfill both criteria.
Finding the symbolic links to represent "only bipeds" and "only moving superhumanly fast" will be very interesting though!
Edit: Oh, as UmbraLux mentions above, "superhumanly fast" might not be a specific enough trigger - what's fastest: an olympic sprinter with Superb Athletics and a stunt, or a newbie WCV with Average Athletics and Inhuman Speed? You might have to set a "speed limit" (probably X shifts on a Sprint action).