Based On GPS Data Analysis Of Tectonic Stress-strain Field And Earthquake Hazard Along The Middle And Southern Segment Of The Tan-Lu Fault Zone

Tancheng-lujiang fault zone is located in eastern China,it is the largest fault zone in the eastern part of China which across the northeast area,Bohai Sea,Shandong,Jiangsu,Anhui and other regions with a total length of about 2400 km.The southern part of the Tancheng-lujiang fault zone which located in the south area of the Bohai Bay has developed a lot in the beginning of the Quaternary such as The Anqiu 7.0earthquake in the 70 years and the Tancheng 8 1/2 earthquake in 1668,which made it one of the the main active earthquake area in China.After the Wenchuan M8.0earthquake in 2008,the post-earthquake effect of the underground fluid has persisted in some parts of the middle-southern area of the Tancheng-lujiang fault zone,and the result of the velocity structure research shows that the exist of medium velocity structure condition which may cause earthquakes with a higher intensity from middle to strong.In 2011,the Miyagi MW9.0 earthquake in Japan caused the magnitude of the coseismic anomalies in the eastern and western regions of the eastern part of China.Many former studies have shown that the subduction of the Pacific plate to the Eurasian plate is one of the main sources of power in the North China.Earthquakes in Japan have an important impact on the Earthquake activity in North China.Historical earthquake,seismicity,modern tectonic activity and other data show that the south central of the Tan-Lu fault zone have a deep seismic structure condition.Therefore,it is of great significance to strengthen the understanding and the analysis of the present crustal deformation characteristics in the south central part of the Tan-Lu fault zone,and to determine the future seismic hazard of the Tan-Lu fault zone and even in North China.Based on the rigid motion model and the least squares configuration method,the stress-strain state of the middle-southern section of the Tan-Lu fault zone is retrieved from the two-stage GPS level field data from 1999 to 2007 and 2013-2015,and on the basis of the obtained results,The seismic hazard of the study area is discussed.Finally,the acknowledge we got as follows:1,The velocity profile of the study area is calculated based on the two-stage GPS velocity field data,and then the comparative analysis is carried out.The results show that the segmental characteristics of the south-central segment of the Tan-Lu fault zone are obvious.The results of the 1999-2007 stage velocity show that the Juxian-Tancheng section is characterized by tensile and extrusion alternation in the vertical fault direction,walking the turning point which located in the right-hand cut or the left-hand cut.The results of the 2013-2015 velocity profile show that the surface strain in the south-central segment of the Tan-Lu fault zone after the Wenchuan earthquake and the Miyagi earthquake in Japan shows an increasing trend,and the whole data shows the right-hand shear and is accompanied by the strain characteristics of the extrusion.By comparing the results of the two-stage velocity profile,it can be seen that the regional strain field in the middle-southern section of the Tan-Lu fault zone after the Wenchuan earthquake and the Miyagi earthquake in Japan has been changed obviously,which suggests that the segment is still affected by the two post-earthquakes' effects,and the Miyagi earthquake in Japan has a more significant effect on the south-central segment of the Tan-Lu fault zone,which is the main reason for the near east-west tensile strain in the south-central section of the Tan-Lu fault zone.2,using the least squares configuration method to calculate the Tan-Lu fault zone in the south of the surface strain rate.The results show that the shear strain in the study area after the Wenchuan earthquake and the Miyagi earthquake in Japan is enhanced,and the area with the most significant increase in shear strain is located in the Juxian-Tancheng section,which may show that the Juxian-Tancheng section still has the post-earthquake adjustment slip.3,It is helpful to calculate the Coulomb stress accumulation rate in the middle and southern part of the Tan-lu fault zone for the evaluation the seismic hazard of the fault.The inversion results of the 1999-2007 data show that the Coulomb stress accumulation rate gradually decreases from the south to the north of the study area.The inversion results of the 2013-2015 data show that the Coulomb stressaccumulation rate in the study area has an increasing trend,and the Coulomb stress accumulation rate of the Anchu section is the largest one,followed by the Xinyi-Sihong section,and the Juxian-Tancheng section is the smallest one,Indicating that the formation of high-magnitude earthquake in Anqiu segment have the greatest risk,followed by Xinyi segment.4,through the discussion of the danger of earthquake in the south-central area of the Tanlu fault zone we found that the region has a strong seismic earthquake environment,and the earthquake risk on each segment is not consistent.According to the new seismic crater in North China,it is speculated that the magnitude of the earthquake that may occur in this segment in the future is between the Tancheng earthquake and the Tangshan earthquake.And from the contrast between the results of previous inverses and the stress-strain analysis of the study area.The risk of earthquakes in Anqiu segment is the highest,followed by Xinyi,and the possibility of the generation of earthquake in Juxian-Tancheng segment is properly lower than the former.