Estimation Of Effects Of Different Earth Models In Crustal Deformation Study

The relationship between motion on the fault plane and the deformation observed on the ground can be described by dislocation theory, Green’s functions can describe the relationship between the fault slip and ground deformation, strain and strain gradient. By means of dislocation theory model, we can use earthquake rupture models to simulate the earthquake deformation, strain and other physical quantities observed at the surface; On the contrary, we can also use geodetic observations(GPS, InSAR, etc.) to invert slip distribution on earthquake rupture surface, and then study the internal dynamics of the earth fault activities, and provide the necessary theoretical basis for research to predict earthquakes, tsunamis and other natural disasters.Since the dislocation theory is introduced to seismology, dislocation theory has been developed rapidly, many scholars have studied the problem of co-seismic deformation based on dislocation theory in different earth models. Okada(1985) summarized and analyzed previous work, gave a complete set of the co-seismic deformation calculating formula in homogeneous half-space medium earth model; because this model is too simple, the results in semi-infinite space often have big error. On this basis, Wang et al(2003) gave the displacement Green’s function based on layered earth model; Considering the of the Earth’s layered structure and curvature, Sun(1992), Sun and Okubo(1993) developed a new dislocation theory based on layered spherically symmetric earth model.Compared with the other dislocation in different earth models, layered spherical earth model is much closer to the real earth model, because it takes earth’s layered structure and curvature into account, calculation precision has been improved, and this provides a more accurate theoretical support for analysing earth deformation observation data. To study the differences between these four different dislocation theories in different earth models more comprehensively, this paper analyzed from both forward and inverse calculating respectively.The main research of this paper includes the following sections:1. Regards to the existing theory of dislocation model(homogeneous half-space, layered half-space, homogeneous spherical and heterogeneous spherical earth model) co-seismic deformations of different point fault models in different situations(depth, magnitude, fault type, etc.) are calculated, and we can analyze the effect of earth’s layered structure and curvature. Then, we use earthquake rapture model(2013 Mw6.6 Lushan earthquake) to calculate co-seismic deformation distribution at the surface in these different types of earth models, analyze the difference of different dislocation theories in forward modeling and different dislocation theory’s applicability.2. Distribution of seismic deformation depends mainly on earthquake fault rupture model, seismic deformation distribution features(regional scope and size) response to different earthquake magnitudes are different, the relationship between seismic deformation distribution and magnitude is nonlinear dependent. We based on spherical dislocation theory to study the co-seismic deformation response characteristics of different type and magnitude, and analyze the relationship between seismic deformation response in the vertical direction of the fault strike and earthquake magnitude.3. Through simulation inversion calculation, we analyzed the effect of the earth’s layered structure on strike-slip and dip-slip fault inversion results at different observation data densities. Then, we take 2001 Ms 8.1 Kunlun earthquake as example, use GPS observations date to invert slip distribution on the fault plane based on dislocation theories in different earth models, and analyze of effect of earth’s layered structure in the inversion calculating and different dislocation theory’s applicability.