Proceedings of the 12th International INQUA meeting on paleoseismology, active tectonic and archaeoseismology

recorded within tectonically stable continental regions. These two events ruptured four individual faults (Bulnay, Tsetserleg, Teregtiyn and Dügen Faults) with a total rupture length of ~676 km (Choi J-H et al., 2018). Detailed mapping of the coseismic rupture based on satellite data shows at least 114 km for the Tsetserleg rupture and ~388 km for the Bulnay rupture. Such a scenario offers a unique opportunity to investigate the occurrence of large earthquakes deep within continental interiors. However, our current understanding of the earthquake behavior of the Bulnay Fault is quite limited. On one side, the remoteness of the area, together with extreme climatic conditions, makes difficult human settlements, resulting in the absence of historical seismicity records. On the other hand, paleoseismic investigations are quite limited. Rizza et al (2015) documented two paleoearthquakes, prior to the 1905 event, the most recent one occurred between 2300 yr and 3250 cal B.P, and before that, one paleoevent constrained between 5000 and 9000 yr ago. Although it could be possible to excavate new trenches to have a more robust and complete earthquake time series, this particular area imposes important limitations in terms of logistics during the classical paleoseismological approach (fault-trenches). The major limitation is the permafrost development in the northern side of Mongolia (Walther & Kam, 2023). Local near-surface extension and contraction of the sediments related to the freeze and thaw process results in cryoturbation of the sedimentary sequence (Bertran et al., 2019a). Additionally, the low rates of sedimentation and the scarcity of datable material (charcoal) yield incomplete paleoseismic records and wide ranges of earthquake age uncertainties. Lake sediments, conversely, are sensitive to seismic shaking, are isolated from external climatic agents by the water column, and provide very high temporal resolution with continuous sedimentation (Strasser et al., 2006; Kremer et al., 2017). Thus, they can be used to extend the knowledge of the temporal distribution of prehistoric earthquakes. In order to reconstruct the past earthquake activity of the Bulnay system, we spent one month in the summer of 2022 collecting eight sediment cores from three lakes around the Bulnay fault (Figure 1). We cored two sites within the Takhilt Lake (96.81356°E, 48.81541°N) located ~80 km south of the Bulnay fault. Three sites within the Oygon Lake (96.516628°E, 49.148542°N), which is located 5 km south of the central section of the fault. Furthermore, three sites were cored within the Sangiyn Dalai Lake which is situated on the fault near the eastern tip of the