The Relocation Of Earthquakes Using Double Difference Algorithm In Tangshan Area And The Analyze Of Coulomb Failure Stress Following The 1976 Tangshan Earthquake

With the incessant construction and development of digital seismic observation network,the density of observation stations has gradually increased.So these stations can provide a good deal of accurate continuous and dependable observation datas for the study of earthquake distribution in Tangshan.Double-difference relocation is a relatively mature relative relocation method.The official observation report was collected to apply to the double difference relocation.The observation repot observed by the Hebei Digital Telemetry Network.And all these datas concentrated on Tangshan and its adjacent areas(117.00 ° ~ 120.00 ° E,39.00 ° ~ 41.00 °N).The time of this report start from January 2009 to December 2018.The residual and the error range of the relocation resualt became much smaller.All these changes proved that the presicion of relocation was improved.After analysising the relocated results of earthquakes location from different dimensions,it sames that the relocated earthquakes gather to some faults and there exists a latent fault.The distribution of the relocated earthquakes reveals that the edge of the earthquakes activities is about23 km.Coulomb failure stress research is an acquainted means to explore the earthquake mechanism.After couculated the coulomb failure stress of the Tangshan Ms7.8earthquake to the Luanxian Ms7.1 earthquake,the result was 0.12-0.2 MPa.By calculating the coulomb failure stress combined the Tangshan Ms7.8 with the Ninghe Ms6.9 earthquake to the Luanxian Ms7.1 earthquake the result was 0.04-0.15 MPa.So it was obtained that the Tangshan earthquake had a trigger effect on the occurrence of the Luanxian earthquake.The coulomb stress under the joint action of the Tangshan earthquake and the Luanxian earthquake has a triggering effect on the Ninghe earthquake.Through the evolution of coulomb failure stress under the joint action of the three big earthquakes in the Tangshan area,it was found that the absolute value of coulomb was gradually expanded then deceleratedslowly.This phenomenon reflect the viscoelastic medium relaxation characteristics of the Maxwell body.The magnitude 1.5 and above earthquakes which occurred in Tangshan and its adjacent areas before relocation and the magnititude 1.0 and above earthquakes after the relocation were projected to the coulomb pictures at the corresponding time.The results showed that the number of earthquakes in the positive stress area was dominant.So we considered that the Tangshan Ms7.8 earthquake,the Luanxian Ms7.1earthquake and the Ninghe Ms6.9 earthquake still have a triggering effect on the occurrence of earthquakes in Tangshan area.