SAN JOSE, Aug. 5 (Xinhua) -- Movement of Coco island plate is causing Costa Rica's Nicoya Peninsula to sink 25 millimeters annually, Costa Rica's National Seismological and Volcanology Observatory said Sunday.

A 26-year study by the observatory on the plate of Coco island, about 500 kms southwest of the Nicoya Peninsula, has shown that the plate not only collides with the peninsula, but the peninsula is incapable of stopping this movement.

Twelve GPS (Global Positioning System) units in different regions of the peninsula are being used to register its precise position to determine its sinking rate, observatory geologists Marino Protti and Victor Cordero said.

Protti said not all of the coastline sinks at the same rate, since "the western coastline rises, while the eastern coastline sinks."

Protti's and Cordero's study is backed by the United States' universities of Santa Cruz, California, and Miami.

These organizations work jointly with Costa Rica's National Emergency Commission, which has been trying to avoid an eventual disaster on the peninsula.