Q estimation based on logarithmic spectral areas with different high and low frequencies

基于高低频对数谱面积差的Q值估算方法

When a seismic wave propagates through subsurface viscoelastic media,the formation absorbs the high-frequency energy of the seismic wave more strongly than the low-frequency energy.As the depth and the off set increase,the diff erence between the logarithmic spectral areas with high and low frequencies gradually increases.Based on this seismic wave characteristic,we have developed a novel Q-estimation method based on logarithmic spectral area diff erence of high and low frequencies(referred to as the LSAD_LH method).In this paper,we derive the theoretical relationship between the Q value and difference of logarithmic spectral areas with high and low frequencies and prove the applicability of the LSAD_LH method using a single-layer medium numerical model.To verify the sensitivity of the LSAD_LH method to bandwidth selection and noise,we compare the LSAD_LH method with two credible methods—the logarithmic spectral ratio(LSR)and logarithmic spectral area diff erence(LSAD)methods using a synthetic model containing the random noise.The results demonstrate that the LSAD_LH method is not highly dependent on bandwidth,and in terms of noise immunity,it is signifi cantly better than the LSR method and has the same advantages as the LSAD method.To further highlight the advantages of the LSAD_LH method,we apply the LSAD_LH and LSAD methods to the vertical seismic profi ling(VSP)numerical simulation of the multilayer media and the fi eld zero-off set VSP data.The application of the two cases proves the applicability of the LSAD_LH method and the accuracy of the high Q-value estimation relative to the LSAD method.Moreover,via the transmission coeffi cient,the LSAD_LH method overcomes the weakness of the LSAD method.

地震波在粘弹性介质中传播时,地层对高频能量的吸收作用强于对低频能量的吸收,因此随着深度的增加和偏移距的增大,高频分量和低频分量的对数谱面积差值会逐渐增大。根据这一特征,本文提出一种基于高低频对数谱面积差法的Q值估算方法(A method for Q estimation based on the logarithmic spectral area difference between high and low frequencies,简称LSAD_LH),推导了品质因子Q值与高低频对数谱面积之差的理论关系,并通过单层衰减介质模型证明该方法估算Q值的适用性。为进一步验证本文LSAD_LH法对频带宽度选择和噪声的敏感度,利用包含有随机噪声的模拟地震记录,将LSAD_LH法与谱比法(LSR)和对数谱面积差法(LSAD)两种方法比较,结果表明:LSAD_LH法对频带宽度选择的依赖性不强;在抗噪性方面明显优于LSR法且与LSAD法具有相同的优势。因为LSAD法受透射系数影响,为进一步凸显LSAD_LH法的优势,本文将此方法应用于数值模拟的多层介质零偏VSP资料和实际零偏VSP资料,两种情况的应用进一步充分证明了LSAD_LH法的适用性和相对于LSAD法在高Q值估算的准确性,并且克服LSAD法受透射系数影响的缺点。