Ripped from Jamie Thomson - http://sqlblog.com/blogs/jamie_thomson/archive/2012/10/17/querying-the-ssis-catalog-here-s-a-handy-query.aspx

SSISCatalog.sql

SELECT event_message_id,MESSAGE,package_name,event_name,message_source_name,package_path,execution_path,message_type,message_source_type
FROM   (
       SELECT  em.*
       FROM    SSISDB.catalog.event_messages em
       WHERE   em.operation_id = (SELECT MAX(execution_id) FROM SSISDB.catalog.executions)
           AND event_name NOT LIKE '%Validate%'
       )q
/* Put in whatever WHERE predicates you might like*/
--WHERE	event_name = 'OnError'
--WHERE	package_name = 'Package.dtsx'
--WHERE execution_path LIKE '%<some executable>%'
ORDER BY message_time DESC