Research On The Characteristics Of Crustal Deformation In Bohai Rim Region

Bohai Rim Region is composed of North China Plain, Yanshan, Ordos, LudongHuanghai active blocks, which is the keen area for the study of modern crustal movement in China. Also it plays a pivotal role in political, economic and cultural filed of China. This region, in which tectonic movement is prominent since the New Geology Time, is one of the earthquakes hardest-hit zone in China mainland. The geological structure is complex and the seismic activity is strong in this region. To get the high accuracy crustal deformation information can provide necessary basic information for studying tectonic deformation characteristics of this region.The development of GPS which as a space geodetic technique, provides technical support for the study of crustal deformation characteristics of this region. In this paper, we use four years continuous GPS data between 2010 and 2013 and two periods of national leveling data to study the characteristics of of horizontal and vertical crustal deformation in the Bohai Rim Region, establish crustal movement and deformation model. At last, we describe the regional deformation and strain characteristic exactly by using the triangle method to get the crustal strain field characteristic parameters.The main conclusion of this paper includes:(1) Based on global and Eurasian plate, we calculate and obtain the earth’s crustal horizontal movement velocity field of Bohai Rim Region. The results show that under the framework of ITRF2008, the earth’s crust of the Bohai Rim Region as a whole towards to south-east, this reflects the status that the mainland of China as a whole move towards south-east. Relative to the Eurasian plate, the move trend of Bohai Rim Region as a whole stay stable, the velocity value of Yanshan region is significantly smaller than other place.(2) The Zhangjiakou-penglai active tectonic zone manifest as left-lateral strike-slip movement, there are relative left-lateral movement between the north and south plate. The Tan-Lu fault zone manifest as staged strike-slip movement, much of the area from Shandong Bohai gulf area north to Liaoning manifest as significant right-lateral strike-slip movement. The differential movement in the both sides of the fault zone in Shandong is not obvious, Shandong central mountain area present rapid southern movement.(3) This paper uses triangle method to calculate the crustal strain field characteristic parameters of Bohai Rim Region include maximum principal strain, superficial expansion, maximum shear strain and so on. Through analysis we can find that high value region of maximum shear strain and superficial expansion in this area is in south Liaoning around Bohai Bay, south-central of Hebei, south-west of Shandong and around fault zone. Comparing with the distribution of maximum shear strain and superficial expansion value of Bohai Rim Region, and combining with history earthquake data, we can find that strong earthquakes tend to occur in the junction of two high value areas, rather than the center of high value area.(4) Yanshan area, locate at the north of northern China plain, manifest as upward movement, the average rose is about 3mm/yr. Hebei plain is descending area, there exists violent descending area which take Hangu, Tianjin, Cangzhou as the center, the biggest drop is about 60m/yr, formed a near NE-SW trending elongated subsidence area. The main reason is the excessive exploitation of groundwater. The west of Laizhou Bay and the belt of Dongying, Heze, Weifang are relativly sink area, the middle, the south and the east of Shandong are rising. The south and east of Laizhou Bay and the coast of Yellow Sea are relativly rising, area around the Yellow River Mouth in the west are relativly slight sink. The coast region of southern Jiaozhou Peninsula is basically downtrend. Liaodong Peninsula in the west of Liaoning is upward area, the average rose is about 1-2mm/yr. Shenyang, Xialiao River estuary and Bohai coast in west Liaoning are sink area, the drop are about 2-3mm/yr, the biggest drop in Liao River estuary is about 8mm/yr. By compareing the distribution of sink area of Bohai Rim Region in different periods, we can find that the significant sink area is essentially unchanged, but the subsiding center have a trend to move towards south-west and the north.