Introduction - Geodesy: Introduction to Geodetic Datum and Geodetic Systems - page 10

Brazil and the tropical rainforests in Southeast Asia, the African primary forest
destruction, and the spread of desertification in some areas all adversely influence
the global climate and could trigger inundation and drought disasters. Therefore, a
global environment monitoring system needs to be established and each country
should have a sound monitoring system. The main measures are to develop remote
sensing satellites, to establish a dynamic geographic information system (GIS), and
periodically to make accurate and quantitative assessments of environmental
changes. Development of such a monitoring system needs the support of geodesy:
the launch of near-Earth satellites requires precise Earth gravity field models, the
launch and tracking stations need accurate geocentric coordinates, and the estab-
lishment of GIS requires information about positions of points and controls.
Geodesy serves indirectly in this system but

is still vitally important and

indispensable.

1.2.5 Applications of Geodesy in Disaster Prevention,
Resistance, and Mitigation

Natural disasters, especially earthquakes, floods, and severe tropical storms, usually
bring huge damage and loss to human beings. According to the statistics of Ministry
of Land and Resources of the People's Republic of China, the average financial
losses caused merely by geological disasters in China have amounted to about 4300
million US dollars each year since 2008 and, in years with frequent disasters, the
loss caused by all kinds of natural disasters can reach one-sixth of the Chinese
national gross domestic product (GDP). Therefore, countries worldwide set great
store on preventing and fighting disasters. At present, excluding tropical storms
(which can by and large be forecast accurately), it is still hard to predict massive
earthquakes successfully, which reflects the inadequacy of man's knowledge of the
science of the Earth. There is still a long way to go to improve our ability to prevent
and mitigate natural disasters, which is an important mission of the geosciences,
including geodesy.
Modern geodetic techniques, especially space geodesy, will be increasingly
crucial in research on the monitoring and forecasting of earthquakes. Most earth-
quakes are distributed along the plate subduction zones and active intra-plate fault
zones. According to historical statistics of earthquakes, the seismic activity of a
seismic zone has a certain statistical periodicity. Geological evidence on prehistoric
earthquakes in the plate subduction zones of the northwest Pacific Ocean has
already been recognized, and the results of geodetic studies on crustal strains are
in accordance with the accumulation of elastic strain in the period between two
earthquakes, which supports the view of the Earth's recurrence period whose
physical ground is the elastic rebound theory. This theory also serves as the basis
for using the geodetic method to monitor crustal strains in a seismic zone over a
long period to provide information for the medium- and short-term forecast of