OOP Wall Anchorage - min. size of wood framing member

1997 UBC Section 1633.2.8.1 required the wood framing member of the wall anchorage assembly in seismic zones 3 and 4 to have a minimum net thickness of 2 1/2". I do not find this requirement in the 2006 IBC, 2007 CBC, nor in ASCE7-05. Is this no longer required and, therefore, a 2x member could be used?

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