Elements of a Quantitative Archaeoseismological Study

16 November 2018 09:00

Klaus‐G. Hinzen(1)

University of Köln

Earthquakes cause ground motions and ground motions can cause damage to engineered structures. Engineering seismology’s main goal is to design structures that withstand such ground motions with the primary goal to prevent casualties. Models for simulating ground motions, given that the seismic source and the travel path parameters are known, can be constructed which help to quantify damage scenarios. In practice often statistical measures of ground motions are used to define the potential dynamic input. By applying a variety of models, the dynamic behavior and capacity of engineered structures can be calculated and their design adapted to meet the earthquake challenges.

In archaeoseismology, the timeline of operation is somewhat reversed. It is a discipline that includes time travel and a forensic approach; i.e., to reconstruct the situation of the site when the damage occurred as opposed to merely modeling a contemporary structure with its usually well‐known design and material parameters. The only available data is the evidence of damage to structures revealed by archaeological techniques in ongoing or completed excavations; in the latter case, documentation may be limited, particularly if the archaeological work started a long time ago. In addition the environmental conditions including seismic site effects might have changed since the damage occurred. Therefore, the task becomes one of starting with the damage, and travel backwards in time, make models of structures and their subsurface, evaluate possible non‐seismic damage causes, estimate ground motion characteristics, and eventually conclude on the existence and character of the assumed earthquake source.

The tools available to the quantitative archaeoseismologist include Laser scanning and photogrammetry to document the current status, Finite and Discrete Element techniques to virtually test structures and a considerable range of methods to calculate synthetic site‐specific seismograms. On‐site data acquisition is often necessary to quantify parameters required for the models, and these include estimates for anthropogenic structures e.g. their natural frequencies and for the subsurface. The complexity of the problem introduces large uncertainties in the results; however, by continuously striving to quantify, these methods can also provide a reasonable estimation of uncertainty, more so than ‘common knowledge’ interpretations of archaeologically documented damage. We use field cases from Greece, Turkey, Israel and Italy to illustrate the quantitative archaeoseismological concept.