Using the 137Cs technique, we assessed spatial variation in soil erosion and its impact on lateral movements of soil organic carbon (SOC) and total nitrogen (total N) in a terraced series and a complex slope in the Longmenshan Fault zone, China. The complex slope derived from three terraced fields with damaged banks, resulting from the 8.0 Wenchuan Earthquakes in 2008. The terraced series and complex slope are the dominant sloping farmland patterns in this area, which represent for earthquake non-affected and affected sloping farmland, respectively. Soil loss occurred over the upper parts of slopes and deposition occurred towards the downslope boundary of each terrace. Also, soil loss occurred on upper terraces and soil accumulation on lower terraces. Net soil erosion rates for the terraced toposequence were estimated at − 3.70 ± 14.38 Mg ha⁻¹ yr⁻¹, indicating the terraced toposequence played an important role in soil conservation. For the complex slope, higher soil erosion rates occurred at the summit and other slope positions with greater slope curvature, and soil accumulation occurred at the toe slope and other slope positions with lower slope curvature (15 m, 25 m, and 40 m). In addition to water erosion, collapses resulting from earthquake and tillage erosion were also important soil erosion processes for the complex slope. Moreover, Net soil erosion rate on the complex slope (4.89 ± 18.03 t ha⁻¹ yr⁻¹) was significantly higher than on the terraced series. SOC and total N inventories showed similar patterns to the 137Cs inventory. Such results confirm that 137Cs can help to trace SOC and total N dynamics on sloping farmland in this area.