Crustal strain fields in the surrounding areas of the Ordos Block, central China, estimated by the least-squares collocation technique

Abstract

The Ordos Block and its surrounding areas play a special role in the kinetic pattern of current tectonic deformation in mainland China (East Asia). In order to better understand the recent crustal deformation and geodynamics of this region, we use GPS velocities and employ the least-squares collocation (LSC) technique to estimate the distribution of the crustal strain rate fields. We calculate the principal components of strains, such as the maximum shear strains, the plane strain gradients and the principal axes of strains. The strain fields obtained in this paper can well portray crustal deformation in the region. Our results show that the relatively higher maximum shearing strain rates are mainly distributed over region surrounding the Ordos Block, indicating these periphery areas have intense crustal activities. Indeed, these periphery areas encompass major active tectonic belts (e.g., the western edge of the Qilian Fold System, the northeastern margin of the Tibetan Plateau and the Taihang Mountain) and active grabens (e.g., Yinchuan, Hetao, Shanxi and Weihe Grabens). Significant plane strain gradients concentrated over the periphery areas of the Ordos Block, indicating that these areas have more intense crustal activity and are more prone to earthquakes. The principle strain rates also show the strain rates for the periphery of the Ordos Block are higher than other regions. The highest strain rates are along the southwestern side of the Ordos Block, indicating that the eastward extrusion dynamics from the Tibetan Plateau may still be the main cause of tectonic deformation in this region. The extensional strains are present in most parts of the Yinchuan, Hetao and Shanxi Grabens. Finally, the characteristics of the strain fields predicted by the LSC technique are discussed, and some interesting tectonic deformation information can be found through further comparison with the strain results predicted by other methods The detailed results and findings obtained in this paper, could further help us better understand the recent active deformation and geodynamics in the surrounding areas of the Ordos Block.