Although it was built as a fully grade separated line, the M1 line operates with shorter trainsets and shorter station platforms than is standard on a traditional metro line, hence its "light metro" designation. The M1 line was later extended from Aksaray towards the western suburbs, reaching Atatürk Airport in the southwest in 2002.[9] Construction of the M2, began on September 11, 1992, but faced many challenges due to the numerous archaeological sites that were discovered during the drilling process, which slowed down or fully stopped the construction of many stations especially at south. Taking into account the seismic activity in Istanbul, the entire network was built with the cut-and-cover method to withstand an earthquake of up to 9.0 on the Richter magnitude scale.[10][11]