| Summary: | Iceland is one of the few places in the world where a Mid-Oceanic Ridge (MOR) is exposed on land, and this gives good opportunity to study geodynamic processes. Spreading of Mid-Atlantic Ocean Ridge (MAR) segments in Iceland began ~60 million years ago. The MAR segments in Iceland have a divergent spreading rate between the Eurasian and North American plates of ~19 mm/yr and are divided into the Western (WVZ), Eastern (EVZ), and Northern Volcanic Zones (NVZ). These zones include 35 active volcanic systems and most of them are located on the plate boundaries. Often a volcanic system consists of a central volcano and an associated fissure swarm. Geothermal activities and Glacial Isostatic Adjustment (GIA) in Iceland occur in addition to the tectono-volcanic activities, adding to the complexity of the geodynamic investigation. Crustal deformations due to tectonic and volcanic activities in Iceland have been studied with geodetic observations since 1938. This study uses geodetic Global Positioning System (GPS) data (1994–2015) collected in the WVZ, EVZ, and NVZ. These measurements suggest that the spreading velocities along profiles parallel to spreading directions are 6.7 ± 0.5 mm/yr (crossing Thingvellir graben) in the WVZ, 14.0 ± 2 mm/yr (between south of Vatnajökull glacier and Torfajökull volcanic system) in the EVZ, and 18.4 ± 1.5 mm/yr (crossing Fremri Námur volcanic system) in the NVZ. The widths of the deformation zones along those profiles are ~50 km in the WVZ, ~100 km in the EVZ, and ~56 km in the NVZ, where ~85–90% of the deformations are accumulated. At the center of Thingvellir rift graben in the WVZ, continuous subsidence of ~4 mm/yr is observed, whereas uplift is dominant in the NVZ and the EVZ. After GIA corrections, the western and eastern parts of the EVZ are dominated by uplifting and subsidence, respectively. In the NVZ, subsidence caused by plate stretching is mostly compensated by magmatic activities in the form of dyke intrusion. However, the center of the rift and the maximum subsidence ...
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