Olives falling from trees prematurely

We have a small olive grove of about 40 trees. I noticed
a significant amount of olives fell of almost all trees. The olive
become brownish and when it is all brown covered the olive falls by the smallest
breeze. I took a picture of some of them from one particular tree, these were not yet on the ground.

I would be happy to know why this happens and what this disease or pest is. Thanks!

Hello friend, check this out:
http://ipm.ucanr.edu/PMG/PESTNOTES/pn74112.html

And this:
https://www.olivesnz.org.nz/wp-content/uploads/2010/09/SFF-Focus-Grove-Project-Diseases-Fact-Sheets-1.pdf