On the role of ancient earthquakes in the building style and in the occupation patterns

15 November 2018 14:40

Stathis C. Stiros (1)

(1) Dept of Civil Engineering, Patras University, Patras 26500, Greece

Have earthquakes influenced building style and occupation patterns in various regions and periods? Despite the recent progress in the study of various aspects of ancient earthquakes, a clear answer to this question is not easy. Clearly, in several cases archaeological and historical data provide evidence of full re-organization of town planning, of changes in the building style, even shifting of inhabitation centers after ancient and sub-modern earthquakes. In other cases, on the contrary, urban patterns seem insensitive to earthquakes, but occasionally, with reversal of the long-term pattern.

There is also evidence that the persistence of old styles/patterns, or the selection of new ones is controlled by a “cost-benefit analysis” of various factors (security, natural resources, broader politico-economic context etc.), by catalyzing role of earthquakes facilitating impeding changes, by migration, and by episodic environmental effects (especially loss of fresh water supply). Understanding these processes requires a detailed and reliable database from various periods and regions, and a synergy between different disciplines, but also refinement and expansion of results of Historical Seismology and Achaeoseismology, which for the moment are not without problems. Just to notice that the theory of aseismic oases inside broad zones of deformation and seismicity collapsed only after a 1995 M6.5 Greek earthquake, and that in critical regions the apparent earthquake rates with time seem inconsistent.

A main reason for these problems is imperfections in the analysis of literary sources, and that apparent highly catastrophic events are usually uncritically adopted, ignoring the limitations of ancient authors and the ideological and political perception and exploitation of physical events through different generations, leading to missed or biased, even physically impossible events. On the other hand, studies of earthquakes based on archaeological evidence tend to a priori adopt deterministic approaches, while the probabilistic and conditional character of palaeoseismological studies is usually ignored, along with the engineering and socio-political context of each case study. Because of these approaches, small deformations of buildings are unconditionally regarded as seismic effects, while Kourion-type destruction layers are regarded as evidence of deliberate actions, and dubious correlations of damages are attempted.

Uncertainty and bias in palaeoseismic data is inevitably reflected and amplified in the study of cultural and historical impacts of earthquakes, and of their impacts in the built environment.