Past Economic Conditions Affect the Reconstruction of the Seismic History of Italy

I analyzed the historical seismic catalog of Italy to assess the factors of the past that could have influenced the capacity of earthquake reporting through time. The analysis was performed looking at the deviation at low magnitudes from the Gutenberg-Richter magnitude-frequency earthquake distribution. I found that the quality of the catalog between the fourteenth and the nineteenth centuries has a nonmonotonic trend, characterized by large fluctuations. The fluctuations are strictly correlated with those of the gross domestic product of the country, supporting the hypothesis that economic conditions affected the production of documents referring to earthquakes (e.g., descriptions of damage to properties or administrative acts for their repair). I found also a marginal improvement during the seventeenth century, probably caused by the diffusion of newspapers. However, such improvement did not increase in the following two centuries, despite the large augment of journals and readers.