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    DigitSeis: Software to Extract Time Series from Analogue Seismograms

    Miaki Ishii, Hiromi Ishii

    analogue seismograms, digitization, DigitSeis software

    Fig.1 Screenshot of DigitSeis version 1.6β(with display in Japanese) showing the short-period vertical recording from Tuczon, Arizona between July 15 and 16, 1945. Digitized traces in colour have been overlain on top of the scanned seismogram image with yellow vertical bars indicating each minute (each hour is also labelled in yellow). The large arrivals in white are those associated with the Trinity nuclear test.

    Fig.2 Part of long-period north-south motion recorded at COL station (College, Alaska) on December 19, 1966.
    (Left) The section of the scanned microfiche image.
    (Right) Same image with digitized traces for two of the lines shown in cyan and magenta.

    A vast amount of analogue seismograms recorded between the end of the nineteenth century and late twentieth century are often inaccessible for seismological research since they are not available as digital time series. This manuscript describes freely available software, DigitSeis, that takes a digital image of an analogue seismic record and returns waveforms either as a function of their x-y position on the image or as time–amplitude information. The overall structure and approach of the software are provided along with how they have evolved over different versions. The effectiveness of the software is demonstrated with three examples. The first example is a long-period east–west seismogram recorded at the Harvard Seismographic Observatory on photographic paper in May of 1938, which contains signals associated with a magnitude¬†7.7 earthquake that occurred off the coast of Northern Ibaraki, Japan. The second example is an analysis of a 35-mm microfilm copy of the short-period vertical seismogram recorded at Tucson, Arizona, on July 16, 1945, that shows blast signals from the first nuclear bomb detonation. The final example uses a 70¬†mm microfiche image of a long-period north–south seismogram recorded at College, Alaska in December of 1966, which shows a pair of earthquakes with nearly identical waveforms. The software is, by no means, perfect, and discussion of its limitations such as the compatibility with pen- and Develocorder-type seismograms is included, as well as comments about challenges of incorporating machine learning into the digitization process.