Strain-Rates from GPS Measurements in the Ordos Block, China: Implications for Geodynamics and Seismic Hazards

A number of devastating earthquakes have occurred around the Ordos Block in recent history. For the purpose of studying where the next major event will occur surrounding the Ordos Block, much work has been done, particularly in the investigation of the Earth’s surface strain rates based on GPS measurements. However, there exist striking differences between the results from different authors although they used almost the same GPS data. Therefore, we validated the method for the calculation of GPS strain rates developed by Zhu et al. (2005, 2006) and found that the method is feasible and has high precision. With this approach and the updated GPS data, we calculated the strain rates in the region around the Ordos Block. The computed results show that the total strain rates in the interior of the Block are very small, and the high values are mainly concentrated on the peripheral zones of the Ordos Block and along the large-scale active faults, such as the Haiyuan fault, which are closely aligned to the results by geological and geophysical observations. Additionally, the strain rate results demonstrated that all rifted grabens on the margin of the Ordos Block exhibit extensional deformation. Finally, based on the strain rate, seismicity, and tectonic structures, we present some areas of high earthquake risk surrounding the Ordos Block in the future, which are located on the westernmost of the Weihe Graben, both the east and westernmost of the Hetao Graben, and in the middle of the Shanxi Graben. Hence, this work is significant in contributing to a better understanding of the geodynamics and seismic hazard assessment.

在近代历史上，鄂尔多斯地块周围发生了多次毁灭性地震。为了研究鄂尔多斯地块周边下一次重大地震将发生在哪里，人们做了大量工作，特别是在基于全球定位系统（GPS）测量来研究地表应变率方面。然而，尽管不同作者使用的几乎是相同的GPS数据，但他们得出的结果却存在显著差异。因此，我们验证了朱等人（2005年，2006年）提出的GPS应变率计算方法，发现该方法是可行的，且具有较高的精度。利用这种方法和更新的GPS数据，我们计算了鄂尔多斯地块周围区域的应变率。计算结果表明，地块内部的总应变率非常小，高值主要集中在鄂尔多斯地块的周边区域以及沿着大型活动断层，如海原断层，这与地质和地球物理观测结果密切吻合。此外，应变率结果表明，鄂尔多斯地块边缘的所有裂谷地堑都呈现伸展变形。最后，基于应变率、地震活动和构造结构，我们提出了未来鄂尔多斯地块周边一些地震高风险区域，它们位于渭河地堑的最西端、河套地堑的最东端和最西端以及山西地堑的中部。因此，这项工作对更好地理解地球动力学和地震危险性评估具有重要意义。