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.
http://www.iag-iaspei-2017.jp/index.html
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)
Description
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)
Description
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.