Conservation and Utilization of Historical Seismograms from Early Stage (A.D. 1904–1948), Mainland China

The history of seismographic observation in the first half of the twentieth century on the Chinese mainland can be divided into three eras. The first era was from 1904 to 1929 when there were some seismographic stations that were built in Mainland China by foreigners. The second era started from 1930 when the stations near Beijing and in Nanjing were built by the Chinese. Advanced seismographic instruments were purchased from abroad, including Wiechert instruments with the heaviest pendulum of 17,000 kg. The development of Chinese seismic observation was disrupted by the Japan invasion and war in 1937. The third era was during a time of war, from 1937 to 1948. The historical changes of seismographic stations and relevant instruments are introduced in this article. Recent effects to preserve the early historical seismograms by means of microfiches and scanning are illustrated. The contribution of these historical seismograms to the compilation of Chinese earthquake catalogs is analyzed. The deficiencies of seismogram utilization and digitalization are pointed out. Future work is proposed.

On the recovery and analysis of historical seismograms

The analysis of historical seismograms has proven to be a fundamental tool to help with the definition of the seismic risk in specific regions. Indeed, modern quantitative reappraisal of relevant earthquakes that occurred before the 1960’s; i.e., prior to both the developments of modern recording instruments and the theoretical progress, has been essential for the assessment of the seismic potential of a source area. However, due to the characteristics (transducing and recording) of the old analog seismographs, the data available are affected by intrinsic uncertainties, and errors can be introduced during the processing of waveform digitization. These drawbacks can seriously influence the quality and reliability of an investigation. In general, no standard technique can be applied when dealing with historical seismograms. Thus, specific tests and cross-checks have to be designed to estimate the limits of each specific analysis. Here, we aim to provide an overview of the whole procedure while focusing on the most crucial steps, from the seismogram recovery to the application of modern techniques for the retrieval of the seismic source information. We also suggest possible checks for the robustness of the data and for the available instrument characteristics, with a description of the effects of various uncertainties on the results that can be obtained. We thus provide useful indications for the analysis of historical seismograms, and also for the correct interpretation of the resulting characteristics of the seismic source.