Pre-instrumental earthquakes in a low-seismicity region: A reinvestigation of the macroseismic data for the 16 November 1931 events in Central Finland using statistical analysis

摘要

The earthquake in Central Finland on 16 November 1931 and its aftershock the same day are investigated. It is the strongest event known to have occurred in this area and thus of importance for understanding the seismicity there. The original macroseismic questionnaires were re-examined using statistical analysis and taking into account the recommendations for intensity assessments according to the European Macroseismic Scale (EMS-92,-98). The data were augmented with contemporary press reports. Test theory was applied when preprocessing the data, and intensity assessment was carried out by means of correspondence analysis. Different approaches were applied to determine the macroseismic field and trace the isoseismals. Some of the practical problems involve the treatment of audible observations. The macroseismic magnitudes were estimated at 4.3 (±0.2) for the main shock and 3.7 (±0.2) for its largest aftershock. Despite the small magnitudes, earthquake light sightings were also reported for the events.