| The uneven horizontal movement of the earth's crust causes each block to squeeze or shift.This phenomenon is closely related to the occurrence of earthquakes and the generation of large-scale geological disasters.At present,GPS has been widely applied to the research of crustal deformation monitoring with its advantages of high precision,large scale,and quasi-real time.Using long-term GPS monitoring data,a high-precision data processing strategy can be used to obtain a high-accuracy velocity field of the crust.A reasonable interpolation method can be used to obtain continuous deformation and strain information of the crust.Based on this,the crust movement deformation and its dynamic characteristics can be analyzed.It is of great theoretical and practical significance to grasp regional crust activity and geological disaster monitoring and early warning.Therefore,this paper selects the junction of the Pacific-North America plate at the junction of the ocean-continent plate and the periphery of the Ordos block at the junction with the“inland”block.These two types of typical tectonic activity areas are different.Using the long-term GPS monitoring data,the spherical least squares collocation method was used to study the characteristics of the crustal deformation field and the strain field in the two regions.Furthermore,the dynamic mechanism of the crustal deformation in the two different types of regions was further explored in combination with the characteristics of the regional geological structure.The main results achieved are as follows:?1?The GPS high-precision data processing strategy was discussed,and the meaning and implementation method of the crustal motion velocity field under different reference frames were analyzed.The method of establishing three kinds of crustal movement velocity field and strain field is analyzed.The spherical least squares collocation method is introduced in detail and the formula is deduced.The biggest advantage of this method is that it takes into account the statistical properties of the measured data and the factors of the actual scale of the area,can truly reflect the regional structural deformation information.?2?The spherical least squares method is applied to the study of the deformation and strain characteristics of the crust along the western boundary of the North American plate at the junction of the"ocean-continental"plates.The results show that the area around the San Andreas fault in the northern part of St.Mary's is the maximum value of the compressive strain,and the magnitude is about-1 1?9?10-7/a;the southwestern part of San Francisco and the northwest of St.Mary's are the maximum domains of the shear strain,and the magnitude is about 6?9?10-7/a.The characteristics of the regional strain field better represent the subduction extrusion dynamics of the Pacific plate to the North American plate.?3?Based on the long-term GPS monitoring data of the periphery of the Ordos block around the"inland"block boundary,the crust GPS velocity field in the region was obtained by adopting a high-precision data processing strategy.The results show that the direction of the overall movement of the area is SE direction,and the magnitude is about 5-10mm/a.After deducting the overall movement trend of the area,it is found that the Ordos block has a more obvious counterclockwise movement;through the typical velocity field profile,it is further revealed that Ordos There are significant differences in movement characteristics between different tectonic zones around the block.?4?The distribution of strain field around the Ordos block around the Ordos block is obtained by spherical least squares collocation method.The results show that the tensile strain of the crustal in the Weihe Basin is significant and the magnitude is 0.5?9?10-8/a approximately;the boundary between the southwestern edge of the Ordos block and the northeastern margin of the Qinghai-Tibet block is a significant compressive-strain region with a magnitude of-1.5?9?10-8/a approximately;the western edge of the Ordos block and the southeastern margin of the Alashan block and the northeast margin of the Qinghai-Tibet block is the maximum value of the maximum shear strain,the magnitude is about 1.6?9?10-8/a,and the maximum principal strain profile further reveals that the values and characteristics of the strain value in the basin structural belt at the periphery of the Ordos block have changed significantly.?5?Based on the obtained crustal deformation and strain distribution characteristics of regional crusts and combined with regional geological structure background,the dynamic mechanism of crustal deformation in these two types of regions,ie,the junction of the“ocean-continent”plate and the“inland”block,is discussed:The North American plate boundary crust activity is mainly affected by the dynamics of subduction and extrusion of the Pacific plate,resulting in structural features of significant earthquakes at the boundary fractures,while the Ordos block is affected by the inhomogeneous forces at its periphery,especially the Qinghai-Tibet Block.The northeast body extrusion force has a significant effect,resulting in a significant development of the faulted basin in the periphery of the block,and a frequent structural pattern of earthquakes and ground fissures. |
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