The characteristics of seismic activity in the ladder zone of Da river hydro-electric plants. The occurrence of natural earthquakes in the ladder zone of Da river hydro-electric plants is the strongest in Vietnamese territory. An earthquake magnitude of M= has been observed in the Tuan Giao and Lai Chau areas, with a b coefficient value (GutenbergRichter law) of | The characteristics of seismic activity in the ladder zone of Da river hydro-electric plants