Abstract
The medieval city of Qalhat was an important trade town along the sea routes in the Indian Ocean. The reasons for the decline of the city are unclear, as the archaeological evidence is inconclusive. Geological field work was conducted and a digital elevation model analysed to test the hypothesis that the city was destroyed by an earthquake. The study area is located along the passive continental margin of the Arabian Plate. The coast shows a set of Pleistocene marine terraces. These landforms are in indication of lithosphere uplift. Faulted terrace fill deposits and deviating fluvial streams indicate rather recent lithosphere deformation. Processes responsible for the deformation are seen as subduction related forebulge uplift, serpentinite diapirism as well as isostatic response to karstification of limestone. We conclude that earthquake activity along the most prominent structural element, the Qalhat Fault, is a plausible reason for the decline of the medieval city.