In Turkey, the North Anatolian Fault (NAF), which accommodates the westward movement of Anatolia with respect to Eurasia, is one of the most active faults in the world.A series of earthquakes (M>6.8) have propagated from east to west during the last century. The next rupture seems to be expected in the Marmara region, south of Istanbul.However, the geometry of this fault becomes more complex in this region. It splits into three branches, one of which borders the southern Marmara Sea and Lake Iznik. This median segment of the NAF (MNAF) has very low seismicity today, and low displacements are recorded by GPS, which leads to considering it inactive. However, the city of Iznik, the cradle of Christianity, has preserved valuable historical evidence in contrast to its observations. Six destructive earthquakes have been mentioned since antiquity. To better understand the seismic hazard in this area, it is necessary to catalogue the seismic activity and locate past ruptures.The use of lakes as natural seismometers has already proved its worth. This thesis has identified two active faults after different geophysical and coring campaigns in Lake Iznik.The first part of this work focuses on the antic period. The study of short (<4m) sediment cores sampled on both sides of the E-W fault passing near the Iznik city shows that the last rupture, dating from 1065 CE, corresponds to a devastating historical earthquake.In addition to this localised rupture, numerous other event deposits are present in the sediments (laterally and temporally). This thesis has (1) differentiated between flood deposits and deposits related to slope destabilisation, most of which are associated with high confidence with historical earthquakes; (2) shown that different types of deposits are recorded for the same earthquake. At the lake scale, the difference in depositional type depends on the source-core distance. One type of deposition is only observed for the 1065 CE earthquake, which takes place in the lake, unlike the others, suggesting that this type of deposition may depend on ground motion parameters. This thesis also presents a compilation of marine and lake palaeoseismological work carried out at the scale of the northwestern part of the NAF, allowing discussion of the limitations of this method. Thus, the concept of basin sensitivity (relationship between the sedimentation rate and the triggering of a slope destabilisation due to an earthquake) does not work in the marine environment, contrary to the lacustrine environment. It is also shown that Lake Iznik records earthquakes from both the NNAF and the MNAF, while the Sea of Marmara seems to record only earthquakes from the NNAF. We also show that contrary to what was previously thought, no earthquakes of Mw>5 have been recorded on the MNAF since the 11 th century, suggesting a significant accumulation of stress on this fault since then. The last part of this thesis focuses on the long term (>2000 years) using seismic and core data. Significant lake level variations have been revealed for mo...