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USA. The fourth seismogram in Fig. 6 shows the 9 April, 1968 Borrego Mountain
(California) earthquake recorded by a WWSSN electromagnetic seismograph at San
Juan, Puerto Rico. All these electromagnetic seismographs belong to the second-
generation of seismic instruments. After the 1960s, electronic seismographs were
developed leading to digital, on-scale recordings of seismic waves. These electronic
seismographs became the dominant seismic instruments for observing earthquakes
starting in the 1980s.
Although seismic signals recorded by electromagnetic seismographs on photo-
graphic paper have a dynamic range of about 1000, they constitute the instrumental
earthquake records we have from about 1910-1980. Although these analog seis-
mograms are far inferior to the modern digital seismograms (with a dynamic range
better than 1,000,000), we can still retrieve many useful information from them as
shown by Kanamori (1988).
8 Discussion
The number of scanned images of the WWSSN and historical seismograms cur-
rently in the SeismoArchives is barely over 1%, numbering only approximately
50,000 out of a total of about 4 million available WWSSN film chips and about
0.5 million available on microfilms of historical seismograms. Nevertheless, it is
a good first step toward preservation of these valuable seismograms. W.H.K. Lee
volunteered to perform some quality assurance tasks and to prepare the prototype
web pages of the current 30 “earthquake archives”. The staff of the IRIS DMC
provided the time necessary to post these earthquake archives online at the IRIS
web site.
The hope is that institutions may be willing to fund scanning of analog seismo-
grams that are of interest to them, and make the scanned image files available after
their research interests are satisfied. So far, two institutions have provided modest
funding for scanning specific sets of WWSSN seismograms: five Italian earthquakes
by the Istituto Nazionale di Geofisica e Vulcanologia (INGV) of Italy, and the 1964
Great Alaska earthquake by the URS Corporation of Pasadena, California.
At present, it costs about $2 US dollars to scan one WWSSN film chip and about
$0.5 US dollars to scan one historical seismogram on microfilm roll. Projections
suggest that it will cost a few million US dollars to scan a significant portion (e.g., 1
million) of the WWSSN and historical seismograms, and at least twice the amount
of money (or equivalent volunteers' time) to perform quality assurance tasks and to
prepare seismogram archives of earthquakes.
As we were preparing this manuscript in the fall of 2006, the USGS Albuquerque
Seismological Laboratory began an 1-year project to scan and create images of
about 60,000 WWSSN more seismograms in order to start constructing archives
of “Earthquake Reference Stations”: San Juan, Puerto Rico; and Honolulu/Kipapa,
Hawaii (C.R. Hutt, personal communication, 2006). In addition, the National Earth-
quake Information Center (NEIC) of the USGS in Golden, CO scanned about
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