Quantifying seismic effects on European populations and economic activities during the Middle Ages.

New maps on population density during the Middle Ages

Thanks to national and international historical seismic catalogues, we already know with accuracy where earthquakes occurred during the high and late Middle Ages in Europe. The real unknown is to gauge how great the impact of these seismic events was on societies and their economies. GIS data management allows us to run a crude analysis to quantify the effects of earthquakes on people and economic activity and produce risk maps. To do this, a set of preliminary maps was created showing the medieval population density for every century in 1000-1550 time-window. These data were obtained from pre-existing studies of medieval demography (for instance, Malanima 2010) which illustrate, for example, regions of Europe with the highest population density during the Middle Ages (Italy and Flanders), and  fluctuations in European medieval population, characterised by progressive growth up to 1348 followed by a profound contraction and a weak recovery. The creation of those maps is still in progress, and a better refinement of  regional-scale outputs is coming.

Population density map, year 1300 AD.
Mosaic of Population density maps in 1000-1500 AD time-window.

To map those regions where economic activities were concentrated, charts can be produced such as the attached map which shows the distribution of cities with a population higher than 10,000 inhabitants in 1300 (from Jotischky, Hull 2005).

Distribution of cities with a population higher than 10.000 inhabitants, 1300 AD.

The next step is to overlay these population and urban density maps with raster maps displaying the macro-seismic effects (isoseismal maps) of each single medieval earthquake with an equivalent Magnitude > 5. The end result, we hope, is a predictive ‘risk’ map  which infers the distribution of seismic-related archaeological contexts in medieval Europe but within a contemporary social and economic context. Understanding the magnitude of earthquakes in the past is important, of course, but it is also interesting to see where and when human exposure to risk was at its highest. After all, a large and potentially devastating earthquake in a sparsely populated region has very different consequences to a seismic episode of exactly the same magnitude which impacts one or more cities.

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