Although construction on Istanbul's first Metro line started in 1992, the first line did not open until September 16, 2000 due to delays caused by the discovery of archaeological findings during construction. As of 2015, there are two "full metro" lines in operation, one in Europe and the other in Asia. There is a plan to build a train tunnel under the Bosporus to connect the two, otherwise separate networks, but it has been delayed many years and there is no target completion date. All sections of the line are designed to withstand an earthquake measuring up to 9.0 on the Richter Scale.