You can't in most locals. Depending on your area, frost level and deck loads come into play.
For example you may be able to place a pier block on a min. 3" slab I've heard, but most building dept. will want a proper footing and pier with rebar, then a min. 1" stand-off post base embedded. Even more will be required in coastal, high wind, earthquake zones, or high termite infestation or all of the above for us here in Cal.
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