Research Of Features In Present Three-dimensional Crustal Movement And Deformation In Liupanshan Region

LiuPanShan region is located in the southeast part of the northeastern margin ofthe Qinghai-Tibet plateau. From the seismic background, Liupanshan region belongsto part of the North-South seismic belt. Also, it is the active tectonic boundary of thestable Ordos block and the strongly deformed Qinghai-Tibet plateau. From thetectonic view, the Liupanshan region is located in central China-Mongolia axis, and isthe transition part of the Ordos block and the Qilianshan fault zone. Due to thenortheast movement of the Qinghai-Tibet plateau, the Liupanshan region is a tectonicactive area. In historical record, several strong earthquakes occurred in theLiupanshan region, such as the600Qinlong M6~7earthquake, the1219Guyuan M7earthquake, the1306south Guyuan M7earthquake, the1622north Guyuan M7earthquake, the1704Longxian M6earthquake, the1709Zhongwei M7.5earthquake,and the1920Haiyuan M8.5earthquake.The seismic risk of the LiuPanShan region received much attention after the2008M8.0Wenchuan earthquake. Many researchers from various fields carried out alot of studies for this region, and believed that the possibility of strong earthquakeoccurrence in the Liupanshan region cannot be ruled out based on the geologicalconditions in the near future. Due to the special tectonic location and strongearthquake potential, the Liupanshan region has attracted much attention from manygeologists and geophysicists.Present-day three-dimensional crustal deformation fields observed by GNSS andleveling measurements can help us to understand interaction between different blocksand explore the dynamic characteristics of the earth.For this thesis, the study area includes the Haiyuan fault, the Liupanshan easternpiedmont fault, the Liupanshan western piedmont fault, and the Longxian-Baoji faultzone. Based on the national important scientific project "China crustal movementobservation network", the major national science and technology infrastructureprojects "China tectonic environment observation network", the major projects ofscientific research, and "Integrated geophysical field observation in China-the eastmargin of Qinghai-Tibet plateau" project, I analyzed the seismic tectonic activities,GNSS data, level data, and InSAR observations. And the present-day crustalmovement of the Liupanshan region and its adjacent area was achieved. At the sametime, the current motion state around the Liupanshan region was also studied by usingthe GPS cross-section, long fault-crossing leveling cross-section measurement, shortfault-crossing leveling cross-section measurement and negative dislocation simulation.Details and the main conclusions are as follows:（1）Based on the previous works implemented around the Liupanshan region, Icarried out tectonic partition and studied the tectonic evolution history. And theneo-tectonic characteristics of the region was also achieved. By collecting thehistorical seismic records, I concluded that the historical strong earthquakes and thecurrent small earthquakes share the same spatial distributions. Most of them is located around the Guyuan and Haiyuan area. However, the Guyuan-Longxian-Baoji arealocated in central and southern Liupanshan region should be considered as a seismicgap. The last M7earthquake happened about1400years ago. Therefore, that seismicgap has the potential for strong earthquake occurrence.（2） Based on the GAMIT/GLOBK software developed by MIT and SIO, Iprocessed the GNSS data for Liupanshan region taken from1999-2007and2009-2013, and achieved the horizontal displacement velocity field. The results showthat the north part of the Liupanshan fault is pressing, while the south part showsextension and strike-slip, with a little thrust component.（3）I collected and processed precise leveling data taken from1970s by usingelevation difference rate as the observations and the vertical deformation rate as theunknowns. We concluded that the vertical deformation rate is positively correlativewith the local topography, indicating successive and uplifting characteristics.（4） Based on InSAR technology, I analyzed the vertical deformationcharacteristics around the Liupanshan region. And three deformation cross-sectionsshow that the central part was uplifting, and the deformation difference between thefault two sides was significant, indicating a deformation state of―strong in the west,weak in the west‖.（5）Through the cross-sections of GPS, long leveling, and fault-crossingleveling data, I concluded that the deformation pattern is different in the north andsouth parts around Liupanshan region. Then I found that the Liupanshan fault waslocked from analyzing the negative dislocation inversion results.