Abstract
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.
Highlights
Major faults represent stable geological structures where huge amounts of strain energy can accumulate in response to stress produced by tectonic movements
Knowing the energy released by major earthquakes, and the slip kinematics, size of the ruptured surface, and distribution of displacement on the fracture is fundamental for the definition of the potential of the causative seismogenic faults, and for the assessment of the associated seismic hazard
Seismic source studies are mainly based on the analysis of the large amounts of digital data that are collected with modern instruments
Summary
Major faults represent stable geological structures where huge amounts of strain energy can accumulate in response to stress produced by tectonic movements. Seismic source studies are mainly based on the analysis of the large amounts of digital data that are collected with modern instruments These data allow for detailed reconstructions of a seismogenic processes. With recurrence times of hundreds or thousands of years, detailed information on the characteristics of an earthquake source is only available for a relatively small number of significant events. On these grounds, investigations into historical earthquakes are fundamental, and, they have become progressively more important in recent years
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