Features of the January 8, 2018, Muong Ang Earthquake in Northwest Vietnam

Macroseismic and instrumental data on the January 8, 2018, Muong Ang earthquake in northwestern Vietnam are comparatively analyzed. Good agreement is found between the macroseismic and instrumental data, which in turn correlate perfectly with the tectonic data. The Muong Ang earthquake consisted of foreshocks, the mainshock, and three series of aftershocks. The first series of aftershocks occurred on the left wall of the Tuan Zao fault, at its terminus in Sha Zung, Muong Ban. Then, aftershocks gradually migrated north-northeast. Finally, aftershocks migrated south. The migration process of aftershocks not only indicates that the seismic activity is largely related to tectonic elements, but also confirms the notion that the Tuan Zao and other faults in this area are active. It can be also assumed that the Tuan Zao fault extends rather far south to the area of Chieng Sho, instead of terminating in Sha Zung and Muong Ban, as shown on modern tectonic maps.