The Muong La–Bac Yen–Cho Bo fault is one of the seismic faults in the northwest region of Vietnam. Neo-tectonic activities and exogenous processes have influenced the drainage system and topographic–geomorphologic features on both walls of the fault. The results of topographic analysis and geomorphological indices have confirmed the active tectonics of the fault during the Neo-tectonic period (Pliocene–Quaternary, about 5 million years). The valley floor width-to-height ratio (V_f) of less than 0.5 indicates the “rejuvenation” of the streams and the obvious influence of tectonic activities on the two walls of the studied fault. The Hypsometric curve (HC) in the study area has a straight–convex shape and the basins on the northeast wall have hypsometric integral index values ranging from 0.46 to 0.481, which are lower and more convex than those of the southwest wall. The Mountain-front sinuosity index (S_mf) from 1.92 to 3.28 along the foot slope of the Hoang Lien Son range (the segment from Than Uyen to Bac Yen and Phu Yen) and the highly variable stream-length gradient index (SL) value on the northeast wall signify the relative tectonic uplift on the northeast wall of the fault. The deformed geomorphological indications (steep cliffs, slip surfaces, etc.) in the field confirm the active tectonics of the Muong La–Bac Yen–Cho Bo fault during the Neo-tectonic period.

The Muong Te fault zone is known as the active tectonic area in Northwest Vietnam, proved by earthquakes with the most recent one of Ms 4.9 on June 16, 2020 and hundreds of aftershocks accompanying with landslides. The neotectonic activities of the study area is asssessed by analysing 61 sub-basins in term of geomorphological indices: Ratio of valley floor width to valley height (V_f), Stream-Length gradient index (SL), Hypsometric integral index (HI), Hypsometric curve (HC) and Index of Relative Active Tectonics (IRAT). As a results, this are has: relative lowV_f corresponding to the terrain of V-shape valleys; SL in large range from 10 to 7000 (gradient - m); straight – convex H ccurve and HI in the range of 0,422 – 0,51 corresponding to the developing phase of river basins; More than 50% of asymmetric basins (AF) due to tectonic impacts. IRAT ranging from 1.25 to 2.5 divided into 3 classes according to the tectonic levels: (1) – strong uplift with - IRAT < 1.5, (2) moderate uplift with IRAT from 1.5 to 2.0 (strong) and (3) weak uplift with IRAT more than 2. The calculated values of the indices are seemed very consistent with the tectonic-geological features of the Muong Te area.