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.
Highlights
Introduction and Aims The city ofQalhat is located on the coastline of Oman
The coastal geomorphology of the shorelines of the northern Indian Ocean in Oman is divers: large beaches characterise the distal parts of alluvial fans in the north of the country, whereas rocky coastlines dominate along the eastern coast where the mountains are close to the sea
Recent deformation of the lithosphere within our study area is seen in faults cutting through terrace fill deposits, in the geomorphology of the terraced landscape and in deflected drainage patterns
Summary
Qalhat is located on the coastline of Oman. The coastal geomorphology of the shorelines of the northern Indian Ocean in Oman is divers: large beaches characterise the distal parts of alluvial fans in the north of the country, whereas rocky coastlines dominate along the eastern coast where the mountains are close to the sea. The coastal zone of Oman is an area of preferred settlement mainly for climatic and economic reasons. In contrast to the interior of the country where arable land is scarce, agriculture is possible within the coastal zone due to exploitation of a shallow aquifer. A further benefit is the access to food resources including sea food. Geological and archaeological research projects currently concentrate on the quantification of coastal dynamics including short term sea level changes in form of tsunami Geological and archaeological research projects currently concentrate on the quantification of coastal dynamics including short term sea level changes in form of tsunami (e.g. Hoffmann et al 2013) and storm surges (e.g. Fritz et al 2010), tectonically induced long term vertical crustal uplift
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