International Association of Geodesy

Commission 3: Earth Rotation and Geodynamics


 The Earth is evolving day by day and its surface and interior are continuously changing. Since we are living on the surface of such a restless planet, it is extremely important to understand the motion and dynamics of the Earth. Geodynamics is the study of the deformation of the Earth. Commission 3 plays a key role to promote science of Earth rotation and geodynamics.

 Monitoring of the rotation is indispensable to our daily life, because it defines time and their parameters are essential to precise determination of satellite navigation systems. Rotation of the Earth is closely related to its internal structure and is also changing. In 17th century, Newton and Huygens proposed different models of the Earthfs rotation; i.e. homogeneous Earth and concentrated mass, respectively. Since then, various discoveries have been made, which deepened our understanding of the Earthfs structure. Now, this procedure of research is being applied to other planets.

 Deformation of the Earth mainly arises accompanied by the dissipation of heat inside the Earth. Heat is transferred to the surface by convection of mantle, which causes motion of tectonic plates. Tectonic plates move and collide against each other on the surface of the Earth. Monitoring of the movements of tectonic plates is essential to understand the generation of earthquakes and other tectonic phenomena and their related natural hazards. Recent earthquakes and volcanic eruptions caused large deformations. Several geodetic techniques revealed associated deformation and help scientists understand their generation process.

 There are several other important factors that affect the Earthfs deformation. Sun, moon and other planets make the Earth deform. This is called Earth tide. The response of ground to the Earth tide also gives us invaluable information on the interior of the Earth. There are a couple of studies showing that its change might be associated with the preparation of earthquake occurrence, as well.

 There is plenty of fluid in and around the solid Earth; atmosphere, hydrosphere, groundwater and the Earthfs core. They are considered to play a key role in the deformation process at a broad scale in space and time. Furthermore they also affect precise positioning with any kind of geodetic techniques.

 Cryosphere is also an important target to be studied, especially from the viewpoint of monitoring of global warming. Melting of ice sheets cause deformation of lithosphere with a long time constant, i.e. glacial isostatic adjustment (GIA), which also gives important information of the structure of the upper mantle.

 Thus, all the processes acting on the Earth are closely related to each other, and issues to be discussed in Commission 3. This commission works to develop cooperation and collaboration in computation, in theory and in observation of Earth rotation and geodynamics. Commission 3 of the term 2015 - 2019 will promote several activities such as symposia and collaborative works. It consists of 5 sub-commissions, one joint study group and 2 joint working groups. These are

SC 3.1: Earth Tides and Geodynamics (Chair: J. Bogusz, Poland),

SC 3.2: Crustal Deformation (Chair: Z.-K. Shen, China),

SC 3.3: Earth Rotation and Geophysical Fluids (Chair: J. Chen, USA),

SC 3.4: Cryospheric Deformation (Chair: S. Abbas Khan, Denmark),

SC 3.5: Tectonics and Earthquake Geodesy (Chair: H. Ozener, Turkey),

JSG 3.1: Intercomparison of gravity and height change (joint with IGFS, Commissions 1 and 2; Chair: S. Rosat, France), 

JWG 3.1: Theory of Earth rotation and validation (joint with IAU; Chair: J. Ferrándiz, Spain),

JWG 3.2: Constraining vertical land motion of tide gauges (joint with Comm. 1; Chair: Alvaro Santamaría-Gómez, France).

Three international symposia will be held in 2016.

SC3.1 will host the 18th International Symposium on Geodynamics and Earth Tides on June 5 – 9, 2016, Trieste, Italy (

Wegener Symposium will be held in Azores, Spain, on 12-15 September under the auspices of SC3.5.

Vice-President Cheng-Li Huang will host a joint IAU / IAG / IERS symposium, Geodesy, Astronomy and Geophysics in Earth Rotation (GAGER2016), during 18 - 23 July 2016 at Wuhan, Hubei, China (

Zheng-Kang Shen, the chair of the SC3.2, will host a special session, "Geodetic Observations, Modeling Of Earthquake Cycle Deformation, And Tectonicsh (SE13), in the coming Asia Oceania Geoscience Meeting on August 1 in Beijing, China.

Session proposals to coming AGU/EGU and other conferences are being prepared by SCfs. Commission 3 will also contribute to the Joint Scientific Assembly of IAG-IASPEI, which will be held in Kobe, Japan, in 2017.