The DMC collects and archives a number of different types of data.
Time Series Data
Time Series Data (or Waveform Data) includes sensor recordings of a variety of (primarily seismological) measurements. This is the primary type of data available from the DMC.
Event Data provides information about earthquakes and other seismic events.
Metadata include station siting and instrumentation information.
The IRIS DMC archives historical seismic data including scanned seismograms and other information from pre-digital sources.
... old seismograms, if properly interpreted, provide invaluable information on earthquakes in the past, and every effort should be made to save them, regardless of their quality, from possible loss and to make copies in an easily readable form.Hiroo Kanamori (1988)
SeismoArchives Seismogram Archives of Significant Earthquakes of the World
The SeismoArchives website features scanned seismograms from historical earthquakes.
The main purpose of these online SeismoArchives is to preserve seismograms and related materials in computer data files so that they are readily accessible online as source materials for research.