Whenever a site collection is deleted, this event will trigger.
Vandal hackers can do a lot of damage by deleting SharePoint sites, since the organization might lose access to a significant amount of data. We will also alert you if a site is deleted from the second level recycle bin.
Remediation
In some cases, it is still possible to restore a SharePoint site that was accidentally deleted. You can restore it from the Recycle bin. Deleted sites will remain in the Recycle Bin, or the second level recycle bin for 30 days.
Microsoft documentation on SharePoint site restore: https://docs.microsoft.com/en-US/sharepoint/restore-deleted-site-collection