Examining the Fidelity of Seismic Data Recovered from Mircoformats

During 1960s and 1970s, substantial numbers of analog seismograms recorded on paper were converted into microfilm or microfiche film chips (Figure 1). Unlike paper records, these microforms are small, and require special equipment to visualize their contents. This project investigates the feasibility of extracting high quality digital data stored on microfiche or microfilm, and determines the best practices and strategies for their scanning. Preliminary examination we have performed on of a limited number of microform recordings suggests that there may be significant differences between data stored on certain subsets of microforms and their corresponding original paper records (Figure 2). The issues may be due to how the microform records were originally generated, in which case, any existing original paper records need to be preserved. Alternatively, the issues may be resultant of how the records are scanned, in which case, better scanning equipment or instructions are needed. This project will help to develop guidelines and best practices that will not only allow for greater standardization and efficiency as future analog data rescue is performed, but also will help to inform priorities for triage of analog records.

Another important issue with microform recordings is the limitation in scanning. In order to obtain the highest possible resolution to discern faint seismograms, only a portion of the microfiche or microfilm can be converted to a digital image file. As a result, this project will also explore how the small image segments can be effectively and efficiently combined to reproduce the full seismogram recording for retrieval of digital time series. Microform records will also be digitized with a range of various scanning parameters to determine the minimum scanning requirements needed to obtain high-quality time series. The knowledge of such requirements will help to ensure that future legacy data rescue is conducted in a manner that allows for the maximal extraction of information.

Figure 1: Flowchart showing the path of information from initial ground motion to digital waveforms. Gray boxes show type of information, and black arrows indicate tools for processing this information.

Figure 2: Zoomed in portions of the seismogram showing the seismic signal from the July 16, 1945 Trinity Nuclear test as observed at Tuscon, Arizona, with (a) a color scan from a paper record and (b) a bi-tonal scan from microform. Note the loss of the signal from (a) to (b). Courtesy of James Dewey, USGS.

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Department of Earth and Planetary Sciences / Harvard University / 20 Oxford Street / Cambridge / MA 02138 / U.S.A. / Telephone: +1 617 495 2350 / Fax: +1 617 496 1907 / Email: reilly@eps.hartvard.edu