I am reluctant to advise you to delete anything, since I don't have access to your computer to verify what exactly is being deleted. The safer approach, that I recommend, would be simply to move your iMovie Events folder to an external drive to free up space on your internal drive. (It should be kept together with the iMovie Projects folder, if you have one.) The discussion below should be read in this light.
It would help if you would post a screen shot of what you are seeing regarding the iMovie Events folder and the iMovie Library 1 file. Also, could you describe your iMovie version history, and how the iMovie Events folder and iMovie Library 1 folder were created?
The iMovie Events folder likely pertains to the earlier iMovie 9 version, that I assume you once had on your computer. If so, it contains the media that is used in the iMovie 9 projects. There should also be an accompanying iMovie Projects folder, that contains the iMovie 9 projects. These are usually found together in the Movie folder on your Mac, but you may have moved them elsewhere. The iMovie 9 Projects folder references the media in the iMovie 9 Events Folder. You need both folders to play and edit an iMovie 9 project. The iMovie 10 architecture is different in that all of the Media, Events, and Projects are contained in one folder, the iMovie Library folder.
The iMovie Library 1 file would be an iMovie 10 library, rather than a file.
When you upgraded from iMovie 9 to iMovie 10, did you do an Edit/Update Projects and Events from within iMovie 10, to bring over your iMovie 9 projects and events into the iMovie 10 library? If so, you can delete the iMovie Events folder (assuming it is an iMovie 9 folder) as long as you don't intend to use iMovie 9 any longer. The iMovie 9 events would have been updated into iMovie 10, so you would still have those as long as you haven't deleted the iMovie 10 library in which you did the update. If you never did the update, you probably can still do so now. Otherwise, deleting the iMovie Events folder possibly could delete some media that is not contained elsewhere, either in the Finder or in iMovie 10.
You might find it helpful to contact Apple Support, as the techs there have the capability of remotely accessing your computer. To contact Apple Support click on the Get Support item in the upper right hand corner of this forum's screen. Then navigate to a place where you can enter your phone number.
-- Rich
