Three-dimensional Numerical Simulation Of Electromagnetic Effects Associated With Natural Earthquakes

People have discovered and recorded electromagnetic phenomena related to natural earthquakes very early,including the space magnetic disturbance and ionospheric disturbance observed by the magnetometer and ionosonde before the earthquake,as well as those measured by GPS.Changes in the total content of electrons in the ionosphere,etc.These phenomena show that with the occurrence of earthquakes,the electromagnetic field in space will change to a certain extent.Therefore,the existing earthquake prediction system can be improved to a certain extent by relying on electromagnetic methods.To achieve this goal,it is first necessary to establish a numerical simulation algorithm for electromagnetic effects associated with earthquakes in three-dimensional space.On this basis,to further improve,and finally establish a corresponding earthquake early warning system.The main research content of this paper is the three-dimensional numerical simulation of electromagnetic effects associated with natural earthquakes.In the process of numerical simulation,in order to eliminate the influence of the singularity of the source,the total field is decomposed into a primary field and a secondary field are calculated separately.The primary field starts from the differential form of Maxwell's equations,establishes a spherical cavity model,and derives the spherical harmonic series solution of each field component.The theoretical formula requires the calculation of two types of high-order bulk Bessel functions.Because the model scale is large and the physical parameters between layers are different,the calculation of bulk quantities will often lead to overflow due to insufficient computer accuracy.Aiming at this problem,this paper adopts the calculation method of multiplying these two types of Bessel functions to solve this problem.As for the calculation of the high-order Bessel function,this article is divided into two parts: low-order and high-order calculations.The low-order uses the traditional recursive formula for calculation,and the highorder uses the high-order approximation.The quadratic field starts from the integral form of Maxwell's equations and uses the staggered grid finite difference method to obtain the numerical solution of the quadratic field.Because the scale of the electromagnetic field generated by underground fault zones and earthquakes is often large,considering the influence of the curvature of the earth,this paper carries out forward modeling in the spherical coordinate system.The frequency distribution of the electromagnetic field excited by the underground fault zone is basically in the ultra-low frequency and extremely low frequency range,and the electromagnetic wave has a very long wavelength,so the influence of the ionosphere is considered in this article.After completing the formula derivation,the design model in this paper considers the spatial distribution of the electromagnetic field excited by the finite-length galvanic source equivalent to the fault zone when there is an abnormal body underground.The influence of the length of the underground fault zone on the field distribution is considered,and the influence of the electromagnetic wave of different frequencies emitted by the equivalent galvanic source on the field distribution is also considered.