Late Quaternary tectonics and seismotectonics along the Red River fault zone, North Vietnam

A study of active tectonic development in Vietnam is of great importance. Right lateral strike-slip offsets along the Red River fault during the Pliocene‐present are determined by analyzing tributaries, Quaternary alluvial fans, river valley from Landsat, SPOT images, detailed topographical maps and field observation. Along the SW fault of the Red River, right lateral offsets of stream channels range between 150 and 700 m (mean offsets of 300 m). Drainage offsets (170–450 m) are found on the eastern branch. Assuming the major phase of incision is visible in this area which is close to the Red River delta due to the onset of Riss glaciation. Using the average length of offset channels and a minimum rate of 100–150 mm/yr for river propagation, we estimate the horizontal slip rates of 2.9 ± 1.7 mm/yr for Song Chay fault, 2.3 ± 1.5 mm/yr for Red River left side fault and 2.1 ± 1.5 mm/yr for Red River left side fault. Several active faults associated with it are observed in Son La area. The Phong Tho‐Nam Pia fault is clearly seen in the geomorphology which separates Tu Le and Song Da rift zones. In normal fault segments striking NW–SE, SW dipping is observed clearly from SPOT images. In the field, triangular facets indicate typical dip slip displacement. Based on different data, vertical slip rate of Phong Tho‐Nam Pia fault is estimated to be 0.2–0.4 mm/y for Pliocene-present, 0.5–3 mm/y for Quaternary‐present and 0.6–1.7 for the present time. Based on various methods, maximum credible earthquakes for different fault segments in Vietnam were estimated.