The Variation of Waveform and Analysis of Composition for the Geoelectrical Field before Moderate or Strong Earthquakes in Qinghai-Tibetan Plateau Regions

详细信息   

• 责任者：Tan Dacheng (Lanzhou Institute of Seismology ; China Earthquake Administration ; Lanzhou 730000 ; China) ; Zhao Jialiu
• 刊名：Chinese Journal of Geophysics
• 出版年：2012
• 卷期：55(3)
• 关键词：地震前兆 ; precursor ; 地电场 ; geoelectric field ; 青藏高原 ; Qinghai-Tibetan Plateau
• 页码：p.875-885
• 图表：6 illus., 25 tables, 3 refs.
• 分类号：0500
• issnNo：ISSN0001-5733
• isbnNo：CN11-2074/P

摘要

Site-selective phenomenon exists in the normal waveforms of the geoelectrical fields of Qinghai-Tibet Plateau and its adjacent areas： rock structure of the sites,cracks and fissure water,tectonic activity and other factors affect the normal waveforms of the geoelectrical field,a large lake will contribute to the occurrence of TGF-A waveforms nearby,TGF-B waveforms will mostly occur in the areas where there are thick Quaternary sediments,high water content,and good water permeability of rocks,while the geoelectrical fields with no diurnal variation are prone to appear in the bedrock mountains where there are intense tectonic activities.Before moderate or strong earthquakes in the region,short-term and impending anomaly of the geoelectrical field has a cluster phenomenon,in which there is a temporal synchronization or a few days′ difference,while spatially it can be distributed near several faults in the region,manifested as a discrete phenomenon.This phenomenon of temporal clustering and spatial scattering is the short-term and impending precursor characteristics of the geoelectrical field in the region.The Σ-Δ summation method is introduced to analyze the usual stability of spontaneous field through the observational data of the geoelectrical field,which indicate that before a moderate or strong earthquake,background value jumps of part of geoelectrical fields are a transformation phenomenon of spontaneous field;the concept and calculation method,in which the TA value is the sum of the first 10 order tidal harmonic amplitude divided by the sum of the first 100 order harmonic amplitude,are established to show from a quantitative point of view that the tidal effect of waveforms of TGF-A,TGF-B and non-diurnal variation are successively reduced;the first order difference method of ΔE is adopted to analyze the higher frequency electromagnetic components in the minute order geoelectrical field monitoring data,usually the high-frequency jumps show a certain degree of randomness and limitedness.By using three different methods of analysis,the features of spontaneous field,the telluric field and high-frequency electromagnetic components are analyzed from the composition of the geoelectrical field,which provides a theoretical and methodological basis for the physical analysis of the geoelectrical field.