Three-dimensional Modeling And Gravity Inversion Of The Crustal Structure Of The Longmenshan Fault Zone

The structural deformation pattern of the Longmenshan fault zone is complex.The analysis and generation of the three-dimensional lithospheric structure is the premise for understanding the active dynamic crustal deformation and seismic dynamics mechanism.Many scholars have carried out geophysical research on this area and accumulated rich two-dimensional section of deep structure.The 3D geological modeling technology is an intuitive expression of the geological body and a way to realize the scientific management and sharing of geological information.This paper summarizes the previous results of the deep structure exploration in the Longmenshan area and established a three-dimensional geological structure model of the area.The main results include:(1)Summarized the complete process of how to construct 3D geological model by Geomodeller and how to modify model through forward and inverse combination.(2)Wavelet analysis and WORMS algorithm were used to study the relationship between gravity field and fault property,and the gravity anomaly identification based on fault property was used in Longmenshan area,which verified that three main fault zones in Longmenshan merged into one in the deep,which was consistent with previous research results.(3)Combing and summarize the main achievements of the existing deep structural section of Longmenshan,select some seismic sounding profiles as modeling data sources.Construct a two-dimensional profile database of deep structures in the Longmenshan area,and establish a corresponding surface model,based on which the final 3D-model of Longmenshan crustal structure was builded.The model was modified by gravity data inversion finally,and the three-dimensional visualization of the Longmenshan crust structure was realized.(4)The model shows that the depth of the Moho surface is around 40?66 km.The boundary of the Longmenshan fault zone is obvious,showing a trend of low in west,high in east and low in north,high in south;the lower crust is thicker in the northwest and thinner in the southeast,with a thickness of 9?31km;The thickness of the middle crust is around 7?19km,which varies irregularly;the thickness of the upper crust is around 22km,which is gradually thinner from north to south;the depth of the interface below the sedimentary layer is around 9km,the depth of the northeast corner is shallow,the southwest corner The buried depth is large.(5)By performing a profile analysis of the profile in any direction,The section across the southern section,the middle section and the northern section of the Longmenshan fault zone shows that the depth of the Moho in the Longmenshan fault zone is slower at both ends and is faster in the middle section.The sedimentary layer in the southern section is thicker and thinner in the north.The sections parallel to and on either sides of the Longmenshan fault zone show that the upper and lower crust of the Songpan-Ganzi block in the northwest of the Longmen Mountains are thicker,while the thickness of the upper crust and lower crust in the Sichuan Basin in the southeast of the Longmen Mountains is thinner.while the thickness of the middle crust and sedimentary layer is not obvious changed.