| Super-shear rupture is a fault rupture phenomenon in which the rupture propagation velocity of a fault in an earthquake exceeds the shear wave velocity of the propagating medium,super-shear rupture earthquakes produce much more severe damage than normal earthquakes of the same intensity.Many scholars have proposed that the 2008 "5.12" Wenchuan earthquake caused such heavy casualties and serious economic losses,not only related to the high intensity of the Ms8.0 earthquake,but also closely related to the super-shear rupture of the earthquake fault.At present,the engineering community still has limited knowledge about the conditions of fault super-shear rupture generation,propagation law and its influencing factors.In order to reveal the generation mechanism and propagation law of fault super-shear rupture,this paper carried out the inversion of the fault slip distribution of the "5.12" Wenchuan earthquake in 2008,the influence of the propagating medium properties on the propagation of super-shear rupture,the interaction and research work on fault rupture process,etc.The main research contents and achievements are as follows:(1)The displacement was obtained by quadratic integration of the acceleration records of some strong earthquakes of the "5.12" Wenchuan earthquake,and the coseismic displacement field of the Wenchuan earthquake was obtained by combining the displacement data obtained by GPS;The slip distribution of the Wenchuan earthquake seismogenic fault was inverted by the coseismic displacement.The following conclusions are drawn: the permanent deformation displacement of the Wenchuan earthquake is centered on the Yingxiu-Beichuan fault zone,and in the front section of the Yingxiu-Beichuan fault zone,the fault has obvious thrust properties;the characteristics of spin-strike-slip;the main slip and rupture areas of the fault are concentrated in Wenchuan and Beichuan.(2)The dynamic rupture process of the Yingxiu-Beichuan section of the main fault zone of the Wenchuan earthquake is simulated,and the influence of the propagation medium on the occurrence of supershear rupture and the propagation of fault rupture is analyzed.The results show that the strength and velocity of fault rupture will increase with the increase of the density of the medium and the Poisson’s ratio to a certain extent;the density and Poisson’s ratio of the propagation medium in the Gaochuan terrace are higher than those in other surrounding areas,and the super-shear rupture phenomenon was produced in the propagation process of the rupture after crossing the Gaochuan terrace.(3)The geometric model of the surface plane of the Longmenshan fault zone of the Wenchuan earthquake is established,and the influence of the interaction between the faults in the Longmenshan on the fault propagation is simulated and analyzed.The results show that the interaction between the faults in the Wenchuan earthquake promoted the rupture propagation of the faults in the Longmen Mountains,so that the fault ruptures of the rear mountain fault zone of the Longmen Mountains and the central fault zone crossed the fault terrace and completed the entire rupture propagation process.And a relatively obvious super-shear rupture occurred in the Beichuan-Qingchuan section of the Longmenshan central fault zone.(4)A finite element model of the Wenchuan earthquake fault was established,and the rupture propagation process of the three-dimensional fault was simulated and analyzed,and the spatial distribution characteristics of the displacement of the fault plane and the ground surface were obtained.The results show that the speed and strength of the fracture will increase sharply after crossing the inflection point,thus promoting the occurrence of super-shear rupture;due to the overshear rupture in the Gaochuan-Beichuan section,the peak displacements of the fault plane and the ground surface are mainly concentrated in this section,which makes the actual rupture of this section more serious than the surrounding areas. |
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