| The three-component seismic data contains one vertical and two horizontal components,Z,X and Y component,while longitudinal wave mainly contained in Z-component,and shear wave contained in X and Y-components.Because of the different vibration direction of shear wave and longitudinal wave,the single shot records of the three components are of different spectrum characteristics and SNR.As spectrum analysis is an important method for seismic data analysis,it paves a way to study the relationship between frequency and amplitude of Z,X and Y-components data.Signal to noise ratio(SNR),as a reliable standard for measuring seismic data quality,is usually used to compare seismic data.Based on the three component seismic exploration project of Yushe Wuxiang,single gun records in the whole area were divided into three types,then the characteristics of five example records were studied.After separating the Z,X and Y components of the example records,the same time window is selected and to analyze the spectrum characteristics of the three components of each record in Fourier transformation,and the spectrum characteristics of the 3C seismic data in the study area are summarized.Then by consulting the literature,we studied all kinds of SNR calculating methods,selected the frequency domain method,calculated the SNR of the records of the 3Cs of the five example records,and sum up the SNR characteristics of the study area.Finally,the spectrum and SNR characteristics of digital geophone Z-component recording and analog geophone recording are compared.Conclusions drawed as the following:(1)The three components have different spectrum characteristics,Usually,the Z-component has the highest main frequency and the largest bandwidth.The spectrum characteristics of X and Y-components are similar and share the same main frequency and the bandwidth,but the X-component energy is slightly higher than the Y-component.In the study area,the energy of X and Y-components is higher than Z components in seismic information above 70 Hz.From the point of view of Z-component,high quality data can be obtained in theexcitation of bedrock or loess.For X and Y-components,bedrock excitation data has wider bandwidth and stronger energy.(2)Different waves don't share main frequencies,neither bandwidth and energy,but they are all affected by the medium itself and offset.Usually,the large offset gather means small amplitude in spectrum curve?But exceptions exist,some gathers have large offset and large amplitude.In the same gather,the main frequency of reflected waves of the target layers decrease with time.If the waves record in large offset and time are characterised as different in mediumand travel time,the effects of travel time is smaller than the medium itself.(3)The SNR calculated by the frequency domain method is influenced by the defined signal interval,if the signal interval is consistent with the main frequency of the analysis,and the energy of the wave is higher than the other wave,the SNR is high,otherwise its low.When the signal interval is changed,the summit of SNR curve moves.In the same record,the T-SNR curves of X and Y-components is similar,while they are different with Z-component.The Z-component has the highest SNR,and the X component is the next.Usually,the Y component has the lowest signal-to-noise ratio.(4)The reflection medium has great influence on SNR,and the SNR is different in different reflection locations.High SNR can be stimulated in both the base rock and the loess,but the SNR of the X and Y-components may be lower than the common data of the base rock,even if the SNR of it's Z-component is very high.The reason is that the absorption and attenuation of converted shear waves in thick loess is serious.(5)The reflection location(time window)and the defined signal interval affect the SNR.The digital detector has higher main frequency and wider frequency band.For the seismic waves above 50 Hz,the amplitude of single DSU3 is larger than three DX-10 stacking records.However,the background noise of DSU3 is more serious than DX-10.(6)From the reflected wave of the coal seam in this experimentation area,the SNR of the digital geophone is more advantageous in various aspects. |
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