In the real study and work, everyone is always in contact with papers. Thesis is a tool to describe academic research results for academic exchange. So, how to write a paper? The following are some typical papers on geophysical principles that I have compiled, hoping to help you.
Title:
Several typical geophysical principles
abstract:
Geophysics is a discipline of geology and mineral resources, taking the whole earth from the solid core to the boundary of the atmosphere as the research object. The basic principles involved cover the comprehensive contents of physics, geochemistry, geology and other disciplines, which requires students' logical thinking ability and numerical calculation ability. This paper focuses on several basic principles necessary to solve geophysical problems.
Key words:
Typical; Geophysics; principle
Judging from the composition of geophysics, there are two main types. One is theoretical geophysics, which studies large-scale and general principles. The second is to explore petroleum, metal and nonmetallic minerals or solve other geological problems, which is called applied geophysics. Obviously, theoretical geophysics is the premise of practical application, and the basic principle of geophysics is the most basic part of theoretical content.
First, the basic principles of the earth's shape and gravity distribution
The earth is a planet in the solar system, with rotation and revolution. Generally speaking, the shape of the earth is an ellipsoid with slightly flat poles and slightly bulging equator. The study of the shape of the earth is a common subject of geodesy and solid geophysics. Its purpose is to determine the shape and size of the earth, the position of ground points and the fine structure of gravity field by using geometric method, gravity method and space technology. The shape of the earth is mainly determined by the gravity of the earth and the centrifugal force generated by its rotation. The earth is very close to a rotating ellipsoid with a long semi-axis of 6378 136 m and a oblateness of 637. Strictly speaking, the shape of the earth should refer to the geometric shape of the earth's surface, but the natural surface of the earth is extremely complex. Therefore, people take the average sea level and the geoid formed by its extension to the mainland as the research object of the earth's shape, because the geoid is very close to the shape of the earth's surface and has obvious physical significance. However, the geoid is not a simple digital surface, so it is impossible to measure and process data directly on this surface. From the mechanical point of view, if the earth is a rotating uniform fluid, then its equilibrium shape should be a rotating ellipsoid. Therefore, it is further envisaged to approximate the geoid with a suitable ellipsoid of revolution. To determine this ellipsoid, we only need to know its shape parameters (long semi-axis A, oblateness α) and physical parameters (geocentric gravitational constant GM and rotational angular velocity ω). The ellipsoid closest to the geoid is called the average earth ellipsoid. If the deviation between the geoid and the ellipsoid can be determined, that is, the gap (geoid gap n) and inclination (vertical deviation θ) between the geoid and the ellipsoid, the shape of the geoid can be completely determined.
The gravity of the earth comes from Newton's law of universal gravitation, that is, any two particles in the universe attract each other, and its gravity is directly proportional to their mass and inversely proportional to the square of their distance. The approximate gravity of the ground point is 980Gal, the equatorial gravity is 978Gal, and the polar gravity is 983Gal. Due to the extreme curvature and day-and-night motion of the earth, gravity tends to increase from the equator to the poles. The magnitude and direction of gravity on the earth are only related to the position of the attracted point, which should be constant in theory, but gravity changes with time, that is, the gravity observed at the same point at different times is different.
Second, the propagation law of earthquakes and elastic waves in the earth.
Seismic wave is a kind of vibration that propagates underground, and it must be related to the elasticity of rock. It is generally assumed that rocks are completely elastic. In the calculation of seismic waves, the earth medium can be regarded as an isotropic complete elastic body. In seismic wave theory, the earth medium is usually regarded as a uniform, isotropic and completely elastic medium, which is only a simplified assumption. Practice has proved that this assumption can greatly simplify the analysis, and in most cases, the results are quite consistent with the observation results. There are two main methods to study the propagation of seismic waves in the earth: dynamic method and kinematic method. The dynamic method is to directly solve the wave equation, study the reflection and refraction of plane waves on the plane interface, seismic surface waves in uniform half-space and parallel layered space, and the free oscillation of the earth with spherical symmetry model. This method is complicated, so I won't introduce it in this book. We introduce the second method: kinematic method, which simplifies the solution of wave equation to the ray theory of wave propagation, and studies the kinematic characteristics of seismic wave propagation in the earth by using the concept of seismic ray.
The study of seismic wave propagation in the earth is mainly based on the following basic principles. One is Huygens' principle, that is, in a uniform elastic medium, a point vibration source generates spherical waves and propagates around. When the distance r approaches infinity, the spherical wavefront has a large radius and a small curvature, and then the spherical wave becomes a plane wave. The second is Fermat's principle, that is, the travel time (propagation) of seismic waves along the ray is the smallest compared with any other path. In other words, waves always travel along the path with the least propagation time, which is also called Fermat's minimum principle and ray principle.
To sum up, Huygens describes the law of wave propagation in dielectric space from the perspective of wavefront, while Fermat's principle describes the law of wave propagation from the perspective of wave ray.
Third, the magnetic phenomenon of the earth and the electrical properties of the earth.
Geomagnetic phenomenon refers to the spatial distribution of magnetic field around the earth. The earth's magnetic field is similar to that of a magnetic dipole located in the center of the earth. Its magnetic south pole (S) roughly points to the geographical north pole, and its magnetic north pole (N) roughly points to the geographical south pole. The distribution characteristics of its magnetic field lines are that the magnetic field direction near the equator is horizontal, while the magnetic field direction near the poles is vertical to the earth's surface. The magnetic field on the earth's surface changes with time under the influence of various factors, and the north and south poles of geomagnetism are geographically opposite. The geomagnetic field includes two parts: the basic magnetic field and the changing magnetic field. The basic magnetic field is the main part of the geomagnetic field, which originates from the interior of the earth and is relatively stable, belonging to the static magnetic field. The changing magnetic field includes all kinds of short-term changes of geomagnetic field, which mainly comes from the interior of the earth and is relatively weak. The variation of geomagnetic field can be divided into two types: quiet variation and disturbance variation. The intensity of the geomagnetic field is about 0.5-0.6 gauss.
According to the detection of atmospheric electrical phenomena, from the point of view of static electricity, the earth and the atmosphere approximately form a leaky spherical capacitor. According to the atmospheric electrical measurement, the electric field near the surface is perpendicular to the surface, and its value is about E= 100V/m in sunny days, while the surface charge density is-8.85×1kloc-0/0c/m2, so it can be calculated that the total negative charge carried by the surface is 4.565438. The total current is about 1350 amps, and the total electric power consumed in the atmosphere is P = 520 billion watts. Due to the rotation of the whole earth, the positive and negative charges are separated, and the positive charges are distributed in the core and the negative charges are distributed on the surface, and then an annular current is generated in the outer layer, and the direction of the current is from east to west (the direction of the current is opposite to the direction of the negative charges), thus generating geomagnetic field from south to north.
Four. conclusion
Understanding the basic theories and principles of geophysics is helpful for students to establish a self-knowledge framework and has a very good combing effect on the overall content of geophysics. The author also suggests that the majority of students in school can study from the most basic content, so as to have certain advantages in future study.
References:
[1] Teng Jiwen. Opportunities, development space and challenges of the times faced by geophysical research in China [J]. Progress in Geophysics, April 2007:11-112.
, Ren, Hua Xilai. Forward modeling and inversion of electromagnetic field in geophysics [J]. Progress of Geophysics, 2007,04:1181-kloc-0/194.
Chen Yuntai, Teng Jiwen, Zhang Zhongjie. Retrospect and Prospect of Geophysics [J]. Progress of Geoscience, 200 1, 05:634-642.
Huo Zhenhua, Dai Shikun, Jiang. Forward modeling of electromagnetic integral equation in geophysics [J]. Progress in Geophysics, 2014,02: 742-747.
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