| Four earthquakes above medium-sized have occurred near Tianzhu earthquake hollow district since the earthquake electromagnetisms in Tianzhu in Gansu province has been observed by China and France, which are Ms 5.8 in Yongdeng in 1995, Ms 5.4 in West Tianzhu in 1996, Ms 5.9 in 2000, and Ms 6.1 in 2003 in Minle-Shandan.Many researchers have done significant study on the phenomenon of electromagnetic abnormality, crustal resistivity change and electric field dimension-detached occurred before Yongdeng earthquake, which recorded by Songshan station. But restricted by the lack of earthquake cases, data and research method, they have not obtained the regularity knowledge and adaptive data processing method of the local earthquake electromagnetic phenomenon.With the support of China-French Advanced Research Plan of International Cooperation which is called PRA project, the thesis does research on the phenomenon mentioned above, including the phenomenon of electromagnetic abnormality, high frequency change and disturb pedigree structural change, uses the data recorded by the stations of Songshan, Daiqian, Jiayuguan and Lanzhou. And interprets the mechanism of earthquake short-arrive electromagnetic phenomenon. By these researches, it has obtained several conclusions and cognitions as follow:(1) Obvious electromagnetic abnormality and high frequency disturbance. Magnetic field and electric field occurred shape abnormality and high frequency electromagnetic disturbance synchronously seven days before Ms 5.8 earthquake in Yongdeng. And it came back normally after the earthquake. Before Ms 6.1 earthquake in Minle-Shandan, the stations of Songshan and Daiqian occurred the similar phenomenon. But the phenomenon of the stations of Jiayuguan and Lanzhou is not clear.(2) The energy of magnetic field and electric field enhanced two to four magnitudes. At the stage of electromagnetic abnormality in the Ms 5.8 earthquake in Yongdeng, the disturbance energy of magnetic field and electric field in Songshan enhanced two magnitudes.At the stage of electromagnetic abnormality in the Ms 6.1 earthquake in Minle-Shandan, the disturbance energy of magnetic field and electric field in Songshan enhanced about three magnitudes, and in Daiqian enhanced about two magnitudes, which is synchronous with Songshan. The 24h~2h periods component of electric field increased totally two to four magnitudes about 20 days before the earthquake. The short periods energy of electric field increased approximately half magnitudes in Lanzhou and Jiayuguan.(3) Typical field short period disturbance pedigree structural change of magnetic field and electric.The course of short period disturbance strengthening is similar in the Ms 5.8 earthquake in Yongdeng and Ms 6.1 earthquake in Minle-Shandan. It shows that the short period disturbance energy persists a lower value about half a month, and then enhances about two to three magnitudes. (4) Combines the phenomenon and mechanism of resistance anisotropism in the earthquakes in Minle-Shandan and in Yongdeng, it interprets the phenomenon and mechanism of magnetic field and electric field by the mechanism of little break transform of electromechanics and viewpoint of"crustal wave-guide". The following is the mechanism of the electromagnetic abnormality wave, the increase of high frequency, and the change of the prominent spectrum of short period. In the later phase of seismogenic stage, there are some macroscopical physical processes: the number of the new micro-crevice has a accelerated and non-line increases,lots of micro-crevtic orientation . The electromechanical transform occurring in the birth phase of the new micro-crevice excitateds synchronized the strong energy component of the short periods electromagnetism. Then the short period electromagnetism disturbs the normal waves of electric field and magnetic field. At last this induces the aberration of wave.(5) When the earthquake is coming, the intensity of electromagnetism has some relationships with the distance from the epicenter. The distance from Songshan, Daiqian, Jiayuguan, Lanzhou to Yongdeng, Minle, Shandan accords whit the calculation about the spread range of the electromagnetic of epicentre in subterranean medium approximately. To the near distance, such as Songshan, Daiqian, the abnormality of wave is very obvious, the part of high frequency vibrates a huge scope, and the disturbance of short time energy increases to 2/3 magnitudes. To the long distance, such as Jiayuguan, Lanzhou, the disturbance of short time energy increases to 0.5 magnitudes, the abnormality of wave is illegible, the part of high frequency has a narrow scope.(6) In Songshan there is no record about the wave aberration of magnetic field and electric field before the occurrence of Ms 5.4 earthquake in west Tianzhu. At the same time the electromagnetism phenomenon about the abundance of high frequency and the change of the prominent spectrum of short period also have no record. According to the elementary qualitative explanation, the special seismogenicenvironment and the mechanism of epicenter may cause to these phenomena.As the results, one thesis has been written, two theses are planned. The results have been communicated in Mar. 2007 in OPGC in CNRS and in LPCE, Orl'eans University, and obtained authorization and recognition of the cooperators. |
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