Purging Audit Data w/ PowerShell
SharePoint 2013 administration is VERY PowerShell centric... and yet we're still learning ways to perform actions that were a single command in the previous STSADM tool. Well, one thing that was easy to do in a prior version was trim SharePoint auditing data from the SharePoint content databases. For customers that have unintentionally allowed the amount of auditing data to grow significantly, forcing a mass trim command can be a very powerful capability. Interestingly, I couldn't find any good, clear, simple examples on how to do this en mass. So, here you go. It's clearly not complicated but took a small amount of digging. Hopefully you find it useful as a good starting point.
# Begin Example Script
Add-PSSnapin Microsoft.SharePoint.PowerShell
$oldestEntryDate = Get-Date "January 1, 2014"
$sitesToClean = get-spsite -ContentDatabase WSS_Content
$sitesToClean | ForEach-Object { $_.Audit.DeleteEntries($oldestEntryDate) }
# End Example Script