Implications for the water level change triggered moderate (M ≥ 4.0) earthquakes in Lake Van basin, Eastern Turkey

The water level in Lake Van has shown alternating rises and decreases in history, causing economical, environmental and social problems over the littoral area. The water level changes were obtained to be in the order of 100 m between 18000 and 1000 B.C., in the order of 10 m between 1000 B.C. and 500 A.D. and relatively stable and fluctuating in the order of a few metres during the past 1500 years. The most recent change of the water level took place between 1987 and 1996, during which the water level increased episodically about 2 m and its altitude changed from approximately 1648.3 m to about 1650.2 m. All these changes were mainly related to climate changes. In this study, the water level changes in the lake after 1860 are compared with the seismic activity of faults lying close to the basin. Temporal correlations of seismicity with the water level changes are very persuasive and dramatic, indicating hydrogeological triggering of the earthquakes. This study shows that 14 M ≥ 5.0 earthquakes and increasing number of 4.0 ≤ M < 5.0 earthquakes accompanied or followed the dramatic (about 1 m or larger) changes of the annual mean of the water level in the lake and that there was a tendency of M ≥ 4 earthquakes to occur between November and February, during which the lake level is low within a year.