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 Earthfs rotation; i.e. homogeneous Earth and concentrated mass, respectively. Since then, various discoveries have been made, which deepened our understanding of the Earthfs 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 Earthfs 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 Earthfs 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 (http://g-et2016.units.it/).
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 (http://gager2016.sgg.whu.edu.cn/).
Zheng-Kang Shen, the chair of the SC3.2, will host a special session, "Geodetic Observations, Modeling Of Earthquake Cycle Deformation, And Tectonicsh (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 SCfs.
Commission 3 hold following sessions in the Joint Scientific Assembly of IAG-IASPEI, which will be held in Kobe, Japan, in 2017.
G04 Earth rotation and geodynamics
Convener: Manabu Hashimoto (Kyoto University, Japan)
Co-convener: Chengli Huang (Shanghai Astronomical Observatory, China), Janusz Bogusz (Military University of Technology, Poland), Matt King (University of Tasmania, Australia), Jianli Chen (University of Texas, Center for Space Research, USA)
The Earth is moving and deforming in response to forces acting on the Earth from outside or inside of our planet. Geodynamics, studies of motion and deformation of the Earth, includes the entire range of phenomena associated with Earth rotation and Earth orientation such as polar motion, Universal Time or length of day, precession and nutation, the observation and understanding of which are critical to the transformation between terrestrial and celestial reference frames. It also includes tidal processes such as solid Earth and ocean loading tides, and crust and mantle deformation associated with tectonic motions and isostatic adjustment etc.
During the last couple of decades, research of geodynamics significantly advanced owing to rapid development of measurement and computation technologies, understanding of the Earth's dynamics and kinematics were deepened. Many geoscientists have come to use the fruit of geodynamics in a more restricted sense to address processes such as plate tectonics and postglacial rebound. Because the Earth as a mechanical system responds to both internal and external forces, and because these responses are sometimes coupled, this session covers studies on the entire range of physical processes associated with the motion and the deformation of the solid Earth. We saw the significant progress of observation in Earth rotation exploiting newly developed observation/measurement technologies, besides traditional VLBI/SLR/LLR/GPS/DORIS, including Super-conductive laser gyroscope measurement, GRACE date on hydrological contribution to earth rotation, Galileo/BeiDou, etc. VGOS will be put into work next year. Studies on developments of new theories or computational techniques, new observation/measurement techniques using emerging technologies are also welcome.
J02 Recent large and destructive earthquakes
Convener: Thorne Lay (University of California Santa Cruz, USA)
Co-convener: Manabu Hashimoto (Kyoto University, Japan)
Large, damaging earthquakes continue to strike globally, producing loss of life and destruction in many regions around the world. In 2015 - 2016 alone, the Gorkha (Nepal), Meinog (Taiwan), Kumamoto (Japan), Muisne (Ecuador), Amatrice (Italy) and other earthquakes resulted in serious regional damage. Earthquake science is essential for revealing the nature of earthquake generation and for extracting lessons from these events to help society reduce the impacts of future events.
Geodesists and seismologists have been cooperating to unveil the secrets of earthquakes. Recent development and deployment of observation/measurement technologies such as space geodetic techniques (real-time GNSS, InSAR, GRACE etc.), global and regional broadband seismic networks, and tsunami recording systems now enable us characterize the full earthquake cycle and to image the rupture process of earthquakes with much higher resolution in space and time than before.
This session welcomes reports on all studies of recent devastating earthquakes with geodetic/seismological/tsunami techniques, including investigations of source process, slip distribution, damage, pre/co/post-seismic deformation, geological/geophysical structure around the source faults, tectonic implications, and other associated phenomena.