Studying On Focal Mechanism And Source Rupture Model Of 2018 Mw7.1 Anchorage Earthquake Using Geodetic And Seismic Wave Data

The study of source properties mainly includes two parts:one is the study of focal mechanism,exploring the types of seismogenic faults and obtaining the geometric parameters of fault plane,which can directly describe the geometric and kinematic characteristics of earthquake rupture;the other is the study of source rupture model,which can obtain the temporal and spatial rupture process and slip distribution,which is of great significance to the study of the kinematic mechanism of earthquake rupture behavior,it can deeply understand the whole process of earthquake from occurrence,development to stop.In this paper,geodetic data（high-rate GPS,conventional GPS,In SAR）and seismic wave data（near and far field broadband seismic data）are used to study the 2018 Mw7.1 Anchorage earthquake of American.The source properties of the event is fully discussed by making full use of the various kinds of data.Based on the g CAP method,the focal mechanism solution of Anchorage earthquake is obtained by seperate and joint inversion using the near-field observation data such as high-rate GPS and broadband seismograph records.At the same time,in order to explore the influence of different velocity structure models on the inversion results,two velocity models（Crut1.0/AEC）are used for comparison and analysis.The inversion results show that:（1）the two nodal planes of focal mechanism solution are north-south strike,dip angles are about 30°and 60°respectively,and the focal centroid depth is 54-55 km,it is an intraplate normal fault event;（2）the source parameters obtained from high-rate GPS waveforms are consistent with those obtained from broadband waveforms and previous research results,which indicates that a small amount of near-field high-rate GPS data can obtain reliable focal mechanism solution（3）the inversion results of the two kinds of data and the two kinds of velocity models are consistent,and close to the focal mechanism results given by the previous researches,which shows that the inversion results are stable and reliable;（4）the addition of high-rate GPS waveforms in the joint inversion provides more effective constraints on the focal depth and improves the depth results.As a result,a more accurate velocity model is helpful to obtain more reliable focal mechanism and reveal more information about source properties of the complex earthquakes.Then,based on the geometric parameters of fault plane obtained from the joint inversion result of focal mechanism solution(strike/dip/rake:nodal plane I 1°/26°/-96°;nodal plane II 188°/64°/-87°.Utilizing the coseismic displacement field obtained from GPS and In SAR Data and the teleseismic P waveforms,the rupture model under finite-fault is inverted,and the temporal and spatial distribution of earthquake rupture process is obtained.In order to obtain a reliable rupture model,the generalized ABIC（Akaike’s Bayesian information criterion）method is used.The inversion results show that the maximum slip of nodal plane I is 3.71m,the average slip is 0.61m,and the total released moment is 4.438×10¹⁹N·m,which is equivalent to the moment magnitude Mw7.03,and the rupture duration is 13.5s.The initial rupture propagates along the downdip direction,and then propagates along the strike to the north of the source;the maximum slip of nodal plane II is 3.51m,the average slip is 0.51m,and the total released moment is 4.177×10¹⁹N·m,which is equivalent to the moment magnitude of Mw7.01,and the rupture duration is 15.5s.The rupture propagates along the downdip direction first,and then unilaterally propagates towards northeast direction.At last,through the analysis of data fitting,rupture centroid depth and ABIC objective function value,the west-dipping nodal plane（nodal plane II）is determined as the seismogenic fault.Finally,the three rupture models are compared,and the seismogenic mechanism and structure are discussed.It is considered that the extensional tectonic environment caused by the rapid change of plate dip angle is the cause of this event.The seismogenic fault is not the nearby Castle Mountain Fault,but a newly developed fault.It is necessary to assess the seismic hazard of this fault.