Measurement of surface deformation in Iceland by precision leveling

Repeated precision leveling across fracture zones in southwest Iceland shows continuous subsidence of existing grabens but no displacement on the existing faults. The rate of subsidence is now similar to the average rate of subsidence during the last 9000 years, as judged by fault displacements in postglacial lavas. The grabens are bordered by normal faults on both sides. The horizontal extension due to displacement of these faults has in the past been approximately equal to the vertical displacement. It amounts to about 70 meters in 9000 years in the Thingvellir graben.