The Simulation Of Six-component Seismic Wave Fields In Isotropic Media

In the process of seismic wave propagation,the particle motion includes not only three independent translational components,but also three independent rotational components.Rotational motion can cause objects to revolve and deform,and can result in serious damage to buildings and structures.Furthermore,a large number of damage investigations resulted from earthquake also verifies the existence of rotational motion in the field of geotechnical and engineering earthquakes.In the multi-wave and multi-component seismic exploration,we can describe the ground motion entirely and understand the nature of the earthquake rupture more comprehensively if we explore translational components and rotational components at the same time,and thus we can obtain information from underground media.The study of six-component wave field propagation characteristics is an important content in the six-component theory research.At present,the theoretical numerical simulation of rotation motion is scarce in China.In order to understand the rotational motion and the wave propagation characteristics of the rotational component,it is necessary to simulate the six-component seismic elastic wave field.On the basis of forward modeling,we can study the wave field characteristics from different media,different source mechanisms and different observation systems.At the same time the differences and similarities between the translational components and rotational components are compared and analyzed,and then the six-component seismic data can be used to separate the different wave fields,suppress noises and reverse the media structure and so on.Based on the basic theory of the first-order velocity-stress elastic wave equation,this paper uses the staggered grid finite difference method to deduce the discrete formula of elastic wave velocity and stress under the two-order time difference precision and the high-order space difference precision.Moreover,the numerical dispersion relation and the stability condition are given,at the same time we introduce the absorbing boundary condition of the splitting complete matching layer(SPML)and the free boundary conditions of the absorption layer boundary whose stress is 0.Finally,we briefly summarized different source types,and realized the six-component wave field simulation in different media with different source types.In this paper,we simulated the seismic wave fields which are generated from the concentrated force source,the expansion source and the shear source respectively in the three-dimensional isotropic full-space homogeneous media.We verified that the differences of the source can affect the elastic wave field.At the same time we realized the stimulation of the six-component seismic wave field in the two-dimensional isotropic homogeneous half-space media and two-layer media,and compared the similarities and differences between translational components and rotational components.Furthermore we analyzed the propagation characteristics of different wave patterns in different media.Finally we simulated Rayleigh wave successfully,and understand the propagation characteristics of surface wave more deeply.The simulation results of different media and different seismic sources show that the staggered grid finite difference method can simulate the seismic wave field quite well.The absorbing boundary condition of the splitting complete matching layer(SPML)can absorb boundary reflection perfectly.Considered the free boundary,the acoustic boundary replacement method can simulate more effectively.It is meaningful to study multi-component because the differences of six-component seismic wave fields have been proved.The rotational component plays a significant role in earthquakes and it should not be ignored.