Inversion of the Activity Characteristics of the Red River Fault Zone Using GPS Data

In order to study the activity characteristics of the Red River fault zone in recent years, the GPS measurements from 1999 to 2014 in the surrounding blocks of the Red River fault zone are modeled by block model, and the rigid block rotations, internal strain rates, fault slip rates and three-dimensional locking degree are obtained. The inversion results show that the block model considering the internal strain can significantly improve the fitting effect to the GPS velocities, the inverted slip rates of the Red River fault are in good agreement with the results of the velocity profiles. The locking degree of the Red River fault is roughly symmetrical that the middle section is relatively strong, and the southern and northern segments are weak. The locking degree of the southern, middle and northern sections are about 0.34-0.52, 0.67-0.75 and 0.26-0.53 respectively from the surface to 15 km depth, and the dextral slip rate deficit were 1.7, 3.0 and 1.4 mm/a, respectively. The distribution of strain field in the study area is calculated by the least squares collocation, it is found that the Red River fault zone is converted from compression in the south to tension in the north. The middle section is in the transfer zone of compression and tension, and its shear strain is lower than the northern and southern sections, which may be due to the stronger locking degree of the middle, so that the fault dislocation is smaller.