Probabilistic Seismic Hazard Assessment Using Legacy Data in Georgia

The Caucasus has a documented history of cataloging earthquakes stretching back to the beginning of the Christian era. Instrumental seismic observation in the Caucasus began in 1899, when the first seismograph was installed in Tbilisi, Georgia. During the Soviet era (1921-1991 in Georgia), the number of seismic stations increased in the region, providing better network coverage and a valuable dataset for seismic research. Data from many thousands of earthquakes recorded by this regional network was stored on paper in seismic bulletins. As part of the project outlined in this article, we pulled together and digitized all available paper bulletins from Georgia and neighboring countries. This allowed significant Limprovements in location accuracy and recalculation of more robust moment magnitudes for earthquakes in this region. It also paved the way for future collaboration and data exchange among the countries in the Caucasus. The resulting earthquake catalog with the new locations and magnitudes was used to conduct a probabilistic seismic hazard assessment to support a major update to the building code in Georgia to align it with the European codes. This article outlines the improvements made to the earthquake catalog in Georgia using legacy data and the new hazard assessment based on this improved dataset.