Modern science is based on experimental data. In most disciplines, these data are acquired in laboratories by means of planned and pre-prepared experiments. By contrast, the laboratory of geophysical research is the entire planet Earth and the experiments are prepared by Mother Nature herself. For data, which have not been observed and recorded today, no full-valued replacement can ever be found.
The basis of observational activities is formed by permanent observatories, which provide long term picture of studied phenomena. Most valuable are long-term continuous homogeneous series of observations on fixed sites, which give evidence of long-term trends of natural processes or anthropogenic influences. Any interruptions deteriorate the series. Observatory data are delivered in nearly real time to data centres and are used by the worldwide geophysical community for research and applications. For example, all available data are used for location of earthquake and estimation of its magnitude. Local network, on the other hand, are built in selected regions important for basic research or applications and are linked to concrete research programs. Temporary mobile networks are usually operated in the frame of international projects.