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Fig. 2 A map showing all seismographic stations for which we could locate seismic bulletin ma-
terials with earthquake observations from before 1921 (from Schweitzer and Lee 2003)
Circulars” (Schweitzer and Lee 2003). Milne seismographs were soon superseded
by more advanced instruments, and the Headquarters of the International Asso-
ciation of Seismology was established in Strassburg im Elsass (now, Strasbourg,
France) by 1904 (Adams 2002).
Seismographs for recording teleseisms were installed at many observatories, es-
pecially meteorological and astronomical observatories. By 1920, about 250 seismic
stations were established (although some operated only briefly), as shown in Fig. 2.
The early enthusiasts included academic professors, Jesuits, and gentleman scien-
tists. Revolutions and wars, however, frequently disrupted progress, especially in
collecting and distributing earthquake information, during the first half of the 20th
century.
2.2 WWSSN and ESSN
In the late 1950s, attempts to negotiate a comprehensive test ban treaty failed, in
part because of perceptions that seismic methods were inadequate for monitoring
the underground environment for nuclear testing (Richards 2002). The influential
Berkner report of 1959 advocated major support for seismology (Kisslinger and
Howell 2003). As a result, the World-Wide Standardized Seismograph Network
(WWSSN) was created with about 120 continuously recording stations, located
over much of the world (except China and USSR) in the early 1960s (Oliver and
Murphy 1971), as shown in Fig. 3. Each WWSSN station was equipped with iden-
tical sets of short-period and long-period three-component seismographs and accu-
rate chronometers. Seismograms were sent to the United States to be photographed
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