TESEO2: Turn the Eldest Seismograms into the Electronic Original Ones

Abstract

Historical seismograms contain a rich harvest of information useful for the study of past earthquakes. This requires proper digitization of the analog records if modern analysis is sought. The digitization procedure usually involves the extraction of the sample sequence directly from the image and, successively, a correction mapping from the (x,y) image coordinates to the amplitude and time of the samples. We present here a different digitization approach that relies on an intermediate parametric vectorial representation of the seismogram trace using piecewise cubic Bezier curves. Our proposed workflow standardizes the historical seismograms vectorization process into various stages insuring proper quality control. We have developed a software for seismogram digitization/vectorization named Teseo2 within the Sismos project (Michelini et al., Eos, Vol. 86, No. 28, 12 July 2005). Teseo2 is a plug-in for GIMP - a multiplatform photo manipulation tool - that extends its functionalities for seismological studies. Teseo2 allows primarily for: - additional operations on the vectorized trace (i.e. resampling and alignment) - supervised vectorization algorithms (color weighted mean) - features of post-analysis of the trace (curvature correction, time realignment) - trace import/export in several formats (such as SAC, SVG, DXF, ASCII, Timemarks distances). In order to keep track of the stages and parameters of a seismogram vectorization, Teseo2 is able to write this information into the image saved in XCF format. Teseo2 is developed following the "Open-Source" philosophy and it is freely distributed under GPL license. Finally, it is cross-platform and the sources, the binaries for Linux, Windows and Mac OS X, are periodically provided on the Sismos web site.