| Summary: | The Caspian Sea is the world's largest closed body of water, and it has a number of unique features, not least, the considerable fluctuations in water level during the 20th century. This water level dropped by 3 m from 1929 to 1977, increased rapidly by 2.6 m during thetwo decades following, and from 1995 a slow rate of change continues. It is likely that the underlying causes of these water level changes are the human activities in the Caspian Sea Basin but literature shows that climate change also had a significant effect. Moreover, these sea level changes occur in a region with a high intrinsic level of seismic activity due to its tectonic setting. Since the sea level fluctuations represent very large scale changes in the loading of the Earth's crust, it seems likely that they are responsible for aspects of the overall seismicity. This is analogous to the problem of Reservoir Induced Seismicity, although even the largest reservoirs are tiny compared to the Caspian Sea. The research reviews the available data to create a reliable database of seismic events in the desired timeframe and location. It was observed that there was a correlation between the Caspian Sea level fluctuations and changes in regional seismicity. Further analysis indicated changes in the b-value of the Gutenberg-Richter Relationship that had an inverse correlation with water level fluctuations, demonstrating that RIS effects are significant. Through statistical examination of the earthquakes listed in the catalogue, the research attempted to find events which could possibly be induced earthquakes. Another large scale effect of the Caspian Sea level changes is investigated on its coasts where the beach profiles were affected by these changes. This sea is a unique laboratory for studies related to sea level rise and several studies have been performed by other researchers on the northern and western Caspian Sea coast. The southern coast, however, has not been adequately explored, thus this research aimed to investigate this part of the coastline. Three field surveys were made along 700 km of the southern coast. In addition to shore sediment sampling, land forms were mapped. Also, deep sediments were sampled by divers along profiles at right angles to the coast at 5 depths up to a depth of 10 m, and hydrographic profiles were surveyed. Laboratory tests were performed on the collected sediment samples. Several classifications were generated based on different factors, and finally, the southern Caspian Sea coast was classified into four categories with respect to their behaviour in response to sea level change. This study investigates the cause and two large scale impacts of the changing water level in the Caspian Sea, and provides a database for future studies. The result can be applied to predict future problems if the water level of the Caspian Sea continues to show considerable changes.
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