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chip). Lamont-Doherty Earth Observatory and the USGS Albuquerque Seismolog-
ical Laboratory (ASL) each hold a complete film chip set of the WWSSN seismo-
grams. The slow degradation of these film chips, however, prompted a pilot scanning
project.
4.1 First Rescue Attempt of WWSSN Seismograms
The idea of scanning the WWSSN film chips within the USGS came about in 1996
by Charles R. Hutt. A limited amount of USGS “data rescue” funding was used
to perform some test film-chip scans. Direct scans of the 70 mm film chips were
found possible if one used scanners having a resolution of at least 3200 dpi. One
of the original ideas was to also digitize the waveforms on the scanned images,
but this was judged to be too expensive. In late 1998, two high-resolution scanners
were purchased to scan as many film chips as possible with the available funding.
The main events of interest at the time were underground nuclear tests, along with
some earthquakes. The event list was chosen in consultation with other government
agencies and researchers interested in the project, resulting in scanning about 30,000
film chips of 156 nuclear events and 78 earthquakes.
The film chips are black and white and were scanned with a resolution of
3200 dpi. This is equivalent to scanning the original 300
900 mm seismogram
at 394 dpi (the seismogram image on the film chip is approximately 8 times smaller
than the original seismogram). The image has been cropped to exclude areas on the
film chip which do not contain the image of the original record, but includes the
record stamp containing station name, component, start and stop date and time of
the record, and magnification. Because the primary selection was on U.S. nuclear
explosion events, the 78 selected earthquakes were made for comparison purposes,
and thus are not necessarily of primary interest to earthquake seismologists. In 2004,
it was agreed that the IRIS Data Management Center would be the perpetual archive
for these and other image files of non-digital recorded seismograms (see Section 5.1
for a description).
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4.2 Second Rescue Attempt of WWSSN Seismograms
In fiscal year 2004, the International Council of Scientific Unions (ICSU) provided
modest funding to the USGS to scan some WWSSN film chips. The USGS provided
a similar amount of “in-kind” support (film-chip storage, work space, management
oversight, etc.). A total of 10,548 film chips were scanned for 117 selected earth-
quakes on the basis of interest to earthquake seismologists. Due to funding limita-
tions, seismograms from only 38 out of 123 WWSSN stations were selected.
The earthquake selection was made by W.H.K. Lee, starting with the Centen-
nial Earthquake Catalog of Engdahl and Villasenor (2002) and selecting the largest
earthquakes down to magnitude of 6.9 for the time period from 1962 to 1974. He
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