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records, and by various methods of telemetry since about 1950s. When we speak
of a seismic station, it may be an observatory with multiple instruments in special
vaults, or a small instrument package buried in a remote unmanned site.
2.1 Early Years
In the beginning of instrumental seismology, observatories with various types of
seismographs operated independently. The observatories were linked by mail, which
could take months. Many seismological studies require seismograms or their read-
ings from multiple stations. For example, arrival times of seismic waves from at least
four well-distributed stations are needed to locate an earthquake satisfactorily. Even
after one managed to get a few seismograms, it was difficult to work with records
from different instruments with poorly synchronized time until after about 1930.
In the late 19th century the need for standardization and for data exchange
was recognized by G. Gerland, J. Milne, and E. von Rebeur-Paschwitz. With
the support of the British Association for the Advancement of Science, over 30
Milne seismographs were placed at locations throughout the British Empire be-
ginning in the late 1890s, and seismogram readings were reported to Milne's
observatory at Shide on the Isle of Wight, England. A global earthquake sum-
mary with seismogram readings was issued by John Milne beginning in 1899, as
shown in Fig. 1 by Milne (1900). These summaries are now known as the “Shide
Fig. 1 Global earthquakes and seismograph stations in 1899, as published in Milne (1900). Num-
bers refer to earthquakes listed in Milne's catalogue and show approximate positions
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