Is the Seismic Hazard in Tunisia Underestimated? An Archaeoseismological Study

The recent seismicity of Tunisia is considered sparse and moderate. A number of historical studies are available, but the archaeological evidence has not been properly used. Pilot studies were carried out at three sites in the less seismic middle part of Tunisia: Roman Thysdrus (Arabic El-Jem), and the Islamic medina (old town) of El-Jem, Sousse and Monastir. A selection of earthquake archaeological effects observed is shown (dropped keystones, fractured or extruded masonry blocks, columns displaced from plinth), marking the potential minimum intensity of shaking. To create this level of damage, local intensity IX is hypothesized. This is certainly higher than the 2007 seismic hazard map produced by WHO, where only medium intensities are indicated for the region. It is suggested that a systematic archaeoseismological study of Tunisia will contribute in improving seismic hazard assessment.