Abstract:Two end members of the Xinmocun lacustrine sediment grain size in the upper reaches of the Minjiang River were inverted using the end member (EM) model of sediment grain. The provenance of sediments and activity of paleoearthquake of each EM were discussed based on the frequency of the EMs, sedimentology analysis, geological and tectonic background. EM1 deposited in lacustrine environments during aseismic period and represents very fine particles brought by wind nearby; EM2 deposited in lacustrine environments in an extremely disastrous condition (e.g. earthquakes, landslides etc.) and represents the dust and few fluvial deposits from nearby sources. Comparative analysis of EM2 percentage, mean grain size, magnetic susceptibility and geochemical ratios (e.g. SiO2/Al2O3, TiO2/Al2O3, CaO/Al2O3, Sr/Al2O3, Rb/Sr, Na2O/Al2O3) indicates that all the indexes vary greatly with grain sizes and possibly point to seismic events. A total of twenty-six possible earthquake events have been identified. Based on the relation of the cumulative thickness of sand sediments with magnitudes of earthquakes, earthquake magnitudes representing seismic events were obtained in this study: sixteen earthquakes of magnitude 5.0~6.0, five 6.0~7.0 and five more than 7.0. Compared to the traditional method of sediment grain size analysis, the EM model can not only determine the EMs and percentage of each component, identify the sediment provenance and dynamic regional sedimentary environment, but also recognize the tectonic events (earthquake, etc.) of sedimentary record. Therefore, this method can better explain the role of tectonic activity in geological and geomorphological evolution.