Hydrogeology and possible effects of the Mw 7.4 Marmara Earthquake (17 August 1999) on the spring waters in the Orhangazi-Bursa Area, Turkey

Nadir, Kaynarca and Ilipinar springs are important water supply sources for the town of Orhangazi, Turkey. These originated from the Middle to Upper Palaeozoic marble formations that overly low-permeability Lower Paleozoic basement schists. Pliocene lake sediments and younger alluvial sediments act as confining layers and contain low volume confined aquifers in their coarser materials to the east of the springs. These springs appear at the boundary of the confining units and along faults and fractures near the town of Orhangazi. Dye tracer experiments at Nadir Spring show that the source of water for Nadir spring is from a different direction than the other two springs, although the chemistry of the water for all three springs is similar. The effects of the Marmara 17 August 1999 Earthquake were relatively minor although temporary changes in flow and turbidity occurred almost immediately after the earthquake. Possible long-term changes may have occurred at a Keramet Hot Spring located approximately 15 km from northeast of Orhangazi, but this spring is not used for water supply. The aquifer that provides most of the water for Orhangazi is highly karstic in nature and has the potential for contamination in the recharge areas and along much of the flow path to the spring. Because of this potential for contamination, the recharge areas of the spring waters should be protected from degradation by uncontrolled land use. In addition, Ilipinar spring has great potential to contribute toward a solution for the chronic water supply problems in Orhangazi and nearby coastal towns.