DigitSeis: A new digitization software for digitizing old analog seismograms
Point of contact: Petros Bogiatzis
DigitSeis is a new open-source, interactive digitization software written in MATLAB that converts digital, raster images of analog seismograms to readily usable, discretized time series using image processing algorithms. We are currently using DigitSeis to digitize old seismograms of the Harvard-Adam Dziewoński Observatory Collection
An analog seismogram is typically subject to various distortions. For example the spiral way of recording around a rotating drum, also known as helicorder drum causes a quadratic distortion (Figure 1a). Additionally, storage conditions, scanning or photo shooting process further distort the seismogram and consequently the final raster image with (e.g., Figure 1b). Such distortions that often cannot be handled deterministically (i.e., by fitting a mathematic distortion model), may deteriorate the digitization and the timing of the traces. DigitSeis automatically identifies and corrects for various geometrical distortions of seismogram images.
Figure 1: Example of various distortions that exist in seismogram images. (a) Helicorder distortion along the traces. The solid line in the middle of the image represents the second-degree polynomial that fits the observed distortion. (b) Distortion along the time marks showing horizontal stretching or shrinkage. The two insets show zoom in around two vertical strips, and the dashed lines are identical in both windows, drawn to follow the position of the time marks in the left strip.
With human supervision, DigitSeis identifies and classifies the different features of the seismogram such as time marks, main trace and noise such as stains and handmade notes (e.g., Figure 2).
Figure 2: An example of classification of traces into three categories, main traces (white), time marks (green) and noise (red).
DigitSeis uses the classification result to digitize both the traces and the time marks, by using the intensity information (Figure 3). Although a large effort has been made to minimize the human input, DigitSeis provides interactive tools to deal with challenging situations such as trace crossings and stains in the paper.
Figure 3: Demonstration of the digitization process.
One of the advantages of DigitSeis is that it corrects time-mark offsets from the main trace to produce continuous seismograms (Figure 4). Furthermore it uses the locations of the time marks to accurately time the traces.
Figure 4: This animation demonstrates the reasoning based upon DigitSeis corrects for the time marks off-set. At the top is shown the digitization result for various relative positions between the normal trace and offset. At the bottom is shown the corresponding mean amplitude of the first derivative of the digitized trace.
Check our poster at the 2016 SSA Annual Meeting in Reno, Nevada
by Petros Bogiatzis*, Isabella Lorrainy Altoé, Alexandra Karamitrou, Miaki Ishii and Hiromi Ishii.
Session: Active Tectonics, Faults and Large Earthquakes, Thursday, April 21, 2016, Room: Tuscany F
This project was supported by the U.S. Geological Survey Earthquake Hazard Program G14AP00016. Earthquake information used in this work is obtained from the International Seismological Centre on-line bulletin (http://www.isc.ac.uk,last accessed March 27, 2015). We also have used data from the Global Seismograph Network and specifically the IRIS/IDA: Scripps Institution of Oceanography (SIO) and IRIS/USGS: Albuquerque Seismological Laboratory (ASL)/USG. The data were provided by IRS Data Management Center.