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In-Depth Information
Quantitative Analysis of Early Seismograph
Recordings
J. Batll o, D. Stich and R. Maci a
Foreword
Seismograms are the most comprehensive and quantitative documents of
ground motion produced by earthquakes. First preserved records account for more
than 100 years of instrumental seismology already, outperforming the time-span
covered by modern broad-band seismic networks. But their uniqueness, as a docu-
ment, prior to the generalization of massive methods of copy and distribution, limits
the usability and availability of the earliest seismograms for research purposes. Con-
temporaneous analysis of old seismograms predated fundamental developments in
quantitative seismology, as well as the digital revolution, suggesting the reanaly-
sis of these unique and valuable records with modern seismological tools for the
direct calculation of earthquake source parameters, at least for the most relevant
events.
However, this is not straightforward: Early seismograms have been recorded
at instruments with low dynamic range and narrow frequency band. Many times
the complementary information required to process the records and to recover
ground displacement, like instrument calibration and time accuracy, has been lost
or is doubtful. In fact, procedures to make old seismograms useful for quanti-
tative analysis are, in many aspects, similar to those needed to process and to
use old macroseismic information. The present contribution reviews the main top-
ics 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 pa-
per seismogram to digital ground displacement, involving digitization, trace cor-
rection and deconvolution of the instrument response. We discuss the potential
and the limitations of such treatments, and review some applications of recov-
ered records in retrieving earthquake source parameters through full waveform
analysis.
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