A study on characteristics of tectonic block motion and tectonic setting of strong earthquakes in northern part of the Shanxi fault depression zone

Introduction Shanxi fault depression zone (SFDZ) is one of important Cenozoic fault basin zones and strong earthquake belts in Chinese mainland. Its northern part has aroused wide research interests due to the complicated tectonics and high activity of strong earthquakes there. Early researches on this depression zone were carried out since 60s of last century (DENG, et al, 1973; DENG, YOU, 1985; LU, DING, 1985; XU, 1990; XU, et al, 1996, 2002). In 90s of last century, the geologica…

A study on characteristics of tectonic block motion and tectonic setting of strong earthquakes in northern part of the Shanxi fault depression zone

This paper makes a systematical study on characteristics of structure and motion of the tectonic blocks in northern part of the Shanxi fault depression zone by means of geometrical and kinematical analysis of the blocks. The ki-netic behavior of the blocks is discussed by comparing associated geomorphic features of fault movement. All analyses and studies are based on a Domino model. The block movement, fault basin extension and their regional distribution are systematically investigated. The result shows: (a) The studied region is divided into sub-regions by NW striking faults: the western, middle and eastern sub-region with crustal extension being 4.46 km, 2.80 km and 1.86 km, respectively. The extensional amount of each block in the region is estimated being generally about 1 km. The calculated result using the block motion model approximately fits the data of geologic survey. (b) Block kin-ematical features are obviously different between the northern and southern part, with the Hengshan block in be-tween, of the studied region. Moreover, the magnitude of the largest historical earthquake in the northern part is about 6, while that in the southern is 7. The faulted blocks in the northern sub-region show northwestward exten-sion, indicating a feature of extensional graben, while the blocks in the southern part manifest tilt motion, extend-ing southeastward, in the opposite sense of fault dipping. Additional tectonic stress generated by block rotation may be one of major factors affecting seismogenic process in the region. It is responsible for the difference in the movement of the block boundary faults and seismic activities between the two sub-regions.