| Earthquake process along with energy accumulation and release process in lithosphere.During this process, lithospheric magnetic field could vary anomaly. In recent years, China earthquake prediction project also proved that lithospheric magnetic field anomaly variety were often related to earthquake epicenters.In order to extract the lithospheric magnetic field anomaly variety, the main approach is to build a high resolution model of lithospheric magnetic field. Due to the measurements for earthquake prediction are all regional, the lithospheric magnetic field modelling method should have three advantages:first, it is suitable for regional geomagnetic modelling; second, it is possible to extract lithospheric magnetic field from the inner field precisely; third, it could represent the tiny lithospheric magnetic field anomaly variety precisely. If it is possible, use field survey data and satellite data together could fill the survey blank area in west China as well as control the results along political boundary. That means the modelling method could also fit the r direction. But not so much method could have all three functions above, not to mention fitting r direction. In this paper, plenty of modelling methods were evaluated and carefully been chose. After model design, computer code, modulus assign and modelling verification processes, the "harmonic spline" might be the suitable method for geomagnetic modelling of China and adjacent areas, which was regarded as the method that have all three functions above as well as r direction fitting. Finally, writer compared other models with "harmonic spline" model in China and adjacent areas, to prove the "harmonic spline" model could reach the anticipate target.Geomagnetic modelling methods such as spherical harmonic analysis, spherical cap harmonic analysis, reversed-spherical cap harmonic analysis, equivalent source method, spline function fitting, biharmonic function fitting, harmonic spline fitting have been compared and selected.In this paper, a huge amount of calculations and research have been done in order to success the mathematical formula Derivation, algebraic formula built and Matlab code programming progress.In order to get a best solution of harmonic spline model, the energy distribution of eigen value has similar features as of Spherical harmonic coefficients. That means different eigen value order may contain energy that belongs to different orders of spherical harmonic coefficients. So we could extract energy that come from different sources by eigen value truncate.During "harmonic spline" calculating, choose suitable "harmonic spline" truncated order is one of the key factors that affect the quality of "harmonic spline" model. Based on plenty of experiments, we choose "harmonic spline" truncated order L=90,and calculate harmonic spline modles as using EMM2010 synthetic data, CGRF ground data and satllite data and their combinations Respectively as candidate models of "2010.0 epoch China and adjacent areas’harmonic spline reference field "。Finaly, we choose the candidate model which use "2010.0 epoch CGRF ground data" and "satellite data reducted to 0km altitude" as "2010.0 epoch China and adjacent areas’harmonic spline reference field ".Then we calculate spherical harmonic coefficients orders from 1 to 15 as main field, and subtract the main field from "2010.0 epoch China and adjacent areas’harmonic spline reference field" to get lithospheric field. At the same time, we calculate regional crustal anomaly field by choose "eigen value truncated order" as 16. Finally, we compared regional crustal anomaly field of MF6, EMM2010, CGRF2010 and harmonic spline model of China and adjacent areas. And proved that the "harmonic spline" model could reach the anticipate target. |
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