The Study On Digitizing Historical Seismograms

Before the construction of digital seismic stations, seismic data has been recorded by mechanical instruments for about 100 years, leaving a number of historical seismograms. Those historical seismograms contain massive valuable earthquake information which is important to seismologists. In order to use modern seismology technology to study the historical seismograms and extend the preservation time of the historical seismograms, it is important to digitize historical seismograms.In this paper, the background and the importance of digitizing historical seismograms is described firstly, and then the key problems of the digitization are researched while the methods to solve those problems are presented at the same time. The main contributions of this paper are:1) Curve extraction from historical seismograms is studied. In this part, the method to extract the curve points and the tangential directions of the seismic curves is proposed by the analysis of the gray profiles of the seismic curves. And in order to facilitate the subsequent analysis and filter the noise points from the extracted curve points, the linking algorithm to link those extracted curve points is described afterwards by using the tangential directions of the seismic curve. The experimental results show that our method can extract curves from historical seismograms with a high accuracy.2) Tracing historical seismograms is studied depended on the work of the curve extraction. The algorithm which combined the inherent characteristics of seismic curves, such as the similarity around the knee point of seismic curves and the motion characteristic that the seismic curves move around with their own equilibrium lines, with the idea of the branch and bound algorithm is proposed to finish the tracing work. The experimental results show that the proposed method can trace historical seismograms automatically and correctly, and the dealing with the intersecting and disconnection seismic curves with a good result.3) The tilt correction for historical seismograms is studied based on the work of the curve extraction. Noticing that historical seismograms contain massive parallel lines which record the time information of the seismograms and the direction of those parallel lines can represent the tilt angle of the seismograms. The method to select the curve from seismograms whose shape is close to the straight line is described firstly, and then its tilt angle which can be used as the tilt angle of seismograms is calculated; finally the tilt correction is achieved by doing the rotation transformation of the original seismograms with the calculated tilt angle. The experimental results show that our method can finish the tilt correction work fast and have a high accuracy.4) The extraction of the timing-marks is studied based on the work of the curve extraction. Seismograms contain a large number of timing-marks which present as regular short lines. The proposed algorithm extracts timing-marks from the curve extraction result of the seismograms, based on the length of timing-marks. The experimental results confirm the reliability of the proposed algorithm.5) In order to further summarize our work, the arc correction for historical seismograms is studied based on knowledge of the low rank. The rank of the image can be used as to measure the self similarity of the image, and the rank of the seismograms which do not occur the arc distortion is lower than that of the seismograms occurring the arc distortion, thus the arc correction can be considered as to find a transformation to minimize the rank of the seismograms. The algorithm to testify that idea is proposed and the experimental results show that the reliability of the proposed algorithm.