Sourav-657741 (7/29/2010)
By default, the audit events are written to the audit target in an asynchronous fashion. Question was not posted properly I guess.
The question was not asking about defaults, so I'm not sure what you mean here. The events can be written in an async or sync fashion, and that is configurable. From the white paper
"...The choice of asynchronous or synchronous is controlled by the QUEUE_DELAY option of the CREATE AUDIT DDL (explained below);..."