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and management of the WWSSN data centre, in charge of the centralization and
distribution of the recorded seismograms over the world. Also, in the 80s, follow-
ing the resolutions approved by the IASPEI and the task of the IASPEI/UNESCO
Working Group on Historical Seismograms, the World Data Centre A (WDC-A)
started collecting, microfilming and archiving of seismograms recorded before 1963
(Glover and Meyers 1982, 1988 and references therein). More recently, applying the
modern digital facilities, other efforts to store copies of the old seismograms as im-
ages in digital format have been undertaken. Among them, we may point to the SIS-
MOS and the EUROSEISMOS projects at European scale (Michelini et al. 2005).
Also Lee impulses a project to digitize part of the microfilm chips of the WWSSN
(see Lee and Benson, this volume).
If we are interested to study an old earthquake, we face the necessity to use old
records. At a first glance, it looks like it involves only the digitization of the relevant
portions of the waveforms in the old recordings, and to process those time series
with the available tools. But, at this point, problems arise. Among them, it can be
mentioned that old seismograms have been recorded with narrow-band, low-range
instruments, now technologically surpassed and let behind. Many times the com-
plementary information (metadata) required to process the records and to recover
ground displacement, like instrument calibration and time accuracy, has been lost
or is doubtful. Even, sometimes, the physical support of the record, the paper itself,
is in poor conditions and physical restoration of the document is needed (Ferrari
and Roversi Monaco 2005). In few words, the use of historical waveforms is not
straightforward. In fact, procedures to make old seismograms useful for earthquake
analysis (restoration, metadata, study of the context) are, in many aspects, similar to
those needed to process and to use old macroseismic information.
In the next sections we report some of our own experience in processing and
evaluating this particularly challenging kind of data, and summarize other efforts
within the seismological community to use early waveforms for the quantitative
analysis of seismic sources. The present contribution reviews the main topics and
methodologies leading to a proper use of old seismograms and related documents,
including the location and distribution of the original seismograms and recording
system information, as well as the sequence from the original paper seismogram to
digital ground displacement, involving digitization, trace correction and deconvolu-
tion of the instrument response. We discuss the potential and the limitations of such
treatments, and show the performance of recovered records of ground displacement
in analyzing earthquake source parameters.
2 Early Seismic Sensors and Recording Systems
The beginning of quantitative recording of earthquake ground motion is more re-
lated to the solution of technical problems that of scientific ones. Even though the
nature of earthquakes sources and shaking was not well understood, it was known
from old times that a suspended mass (a pendulum) oscillates with earthquakes.
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