Seismogenic structures and velocity structure characteristics of middle-north section of red river fault and adjacent areas

The Red River fault is a Holocene active fault between the Indo-China plate and Yangtze plate, its great earthquake risk has gained attention. The middle-north section and nearby areas of the fault can be divided into three tectonic units. In the study, the crustal velocity structure images and accurate earthquake locating results were obtained for various zones by using the tomoDD method. The results showed that the northern and middle section of the region were characterized by low-velocity anomalies in NW and NS directions, and such feature became more obvious as the depth increased. On the west section, large-scale low-velocity anomalies were correlated with the Kainozoic volcanic zone. In addition, from the results of stress drop and velocity structure, the correlation between them is not obvious. Our study may help to understand seismogenic structures of complex fault systems in the Middle-north section of Red River Fault and adjacent areas.