Hi Priyesh,
I assume that you are referring to the ASM event logs which display things like illegal requests that were blocked. If that is correct then I believe I can answer your question. Those event logs are stored in a mysql database. That database is limited to 3 million records or 2 GB in size (whichever comes first). There is then an automatic cleaner that will remove the older records to make room for newer records when the limits of the database are being reached.
So to answer your question, there is no specific set number of days that it will store that data. It just depends on the size and number of requests that are being logged and how fast they are filling up the database. If you are finding that some of your event logs are being removed too quickly then my recommendation would be to use a remote logging profile to log the events to a remote server.
I hope that this helps answer your question.
-Nathan F