Feasibility Study on Determining Focal Mechanism Solutions of Small Earthquakes Using the Velocity Amplitude Ratio of -and -Waves

The focal mechanism parameters of small earthquakes are determined by the maximum velocity and displacement amplitude ratio of the direct ^-P- and ^-S-waves recorded by digital stations. The displacement is obtained from the velocity by emulation, and the two results are compared and analyzed. Results of theoretical analysis and practical measurement indicate that the two results of velocity and displacement are consistent, and it is feasible that the maximum displacement amplitude ratio be replaced by the maximum velocity amplitude ratio of the direct ^-P-and ^-S- waves recorded by regional seismic networks when determining focal mechanism solutions of small earthquakes.     

利用ML振幅研究地壳横波Q值Ⅱ:Q横向变化特征

利用中国地震年报(1984～2004年)测定M_L所用的54000余条区域地震最大振幅数据,采用二维层析成像方法反演中国大陆地壳介质品质因子Q₀结构.反演结果表明,中国大陆地壳介质品质因子Q₀平均为370,Q₀横向变化量可达±200.在整个研究区解的分辨率能够达到3°×3°,大部分地区能够达到2°×2°.Q₀的变化显示出与地质构造分区相关的特征：低衰减 (高Q₀值) 异常区主要分布在塔里木盆地、四川盆地、鄂尔多斯高原及华南地区,鄂尔多斯高原北部Q₀值最高;高衰减异常区(低Q₀值)主要分布在青藏高原以东的川滇地区、华北平原、渤海湾,最低Q₀值在渤海湾地区,天山、祁连山和汾渭地堑Q₀也呈较低异常变化.总体看来,构造上稳定的克拉通地台的介质品质因子Q₀较高,而构造上活动的地区往往Q₀较低,显现出区域的衰减变化特征与地壳结构和区域构造之间的密切关系.     

利用ML振幅研究地壳横波Q值Ⅱ:Q横向变化特征

利用中国地震年报(1984～2004年)测定M_L所用的54000余条区域地震最大振幅数据,采用二维层析成像方法反演中国大陆地壳介质品质因子Q₀结构.反演结果表明,中国大陆地壳介质品质因子Q₀平均为370,Q₀横向变化量可达±200.在整个研究区解的分辨率能够达到3°×3°,大部分地区能够达到2°×2°.Q₀的变化显示出与地质构造分区相关的特征：低衰减 (高Q₀值) 异常区主要分布在塔里木盆地、四川盆地、鄂尔多斯高原及华南地区,鄂尔多斯高原北部Q₀值最高;高衰减异常区(低Q₀值)主要分布在青藏高原以东的川滇地区、华北平原、渤海湾,最低Q₀值在渤海湾地区,天山、祁连山和汾渭地堑Q₀也呈较低异常变化.总体看来,构造上稳定的克拉通地台的介质品质因子Q₀较高,而构造上活动的地区往往Q₀较低,显现出区域的衰减变化特征与地壳结构和区域构造之间的密切关系.     

基于人工电离层扰动对地-电离层波导传播的VLF波的影响

基于低电离层加热理论和甚低频电波在地-电离层波导中传播理论,建立低电离层扰动对甚低频电波传播影响的分析模型,并利用实验数据验证了该模型的正确性.据此模型,研究了加热功率、加热波极化以及背景参数所导致的低电离层扰动对不同频率甚低频电波传播的影响.结果表明,低电离层扰动越强,则通过该区域内甚低频波幅度和相位的相对变化越强,通过研究地-电离层波导甚低频信号通过人工扰动区域后幅度和相位的变化,可望用于诊断人工电离层扰动强度.     

Reflection and transmission of inhomogeneous waves in a composite porous solid saturated by two immiscible fluids

This paper is concerned with reflection and transmission of a plane, elastic, and inhomogeneous wave striking obliquely at some discontinuity inside a porous medium composed of two distinct solids and saturated by two immiscible fluids. It is found that four P‐ and two SV‐waves are reflected, whereas four P‐ and two SV‐waves are transmitted at the interface. All reflected and transmitted waves are inhomogeneous in nature and specified with different directions of propagation and attenuation vectors. An expression for the Umov–Poynting energy flux vector is derived for the system. Continuity of energy flux along normal to the interface gives 12 required boundary conditions. Expressions of amplitude and energy ratios of various reflected and transmitted waves are derived. Variations in amplitude and energy coefficients of reflected and transmitted waves with angle of incidence are numerically studied for a porous matrix composed of shaley sandstone and clay, saturated with water and oil. The effects of change in oil saturation and volume fraction of clay are also observed on amplitude ratios. Numerical simulation reveals that the change in sign in the difference of capillary pressure across the interface causes jump in the values of amplitude ratios of all waves.     

基于GPS连续运行基准站的中国区域共模误差研究

共模误差是GPS台站位置时间序列中的主要误差源之一,分离和消除共模误差可以探测到原先淹没在噪音中的微弱信号。本文对中国260个卫星导航定位基准站2011～2018年的数据进行处理,获得了位置时间序列,采用主成分分析（PCA）方法对其扣除构造运动等形变信号后的残差序列进行区域共模误差分析。结果表明,PCA方法有效地提取了中国区域共模误差,经过滤波后时间序列的信噪比明显提高,第一主分量空间分布均一,第二主分量空间分布呈现明显的梯度变化,表明第二主分量不是少数台站的局部效应,是对第一主分量的补充和修正,中国区域的共模误差分析不能忽略二阶分量。对振幅调制的影响进行了对比分析,发现顾及振幅调制的共模误差不仅明显减弱了年周期的特征,还显著降低了闪烁噪声,表明由于参数过于简化而未被估计的“信号”会演变成共模误差,未被正确模型化的“信号”会影响区域滤波的准确性。     

Frequency‐ and angle‐dependent poroelastic seismic analysis for highly attenuating reservoirs

We extend the frequency‐ and angle‐dependent poroelastic reflectivity to systematically analyse the characteristic of seismic waveforms for highly attenuating reservoir rocks. It is found that the mesoscopic fluid pressure diffusion can significantly affect the root‐mean‐square amplitude, frequency content, and phase signatures of seismic waveforms. We loosely group the seismic amplitude‐versus‐angle and ‐frequency characteristics into three classes under different geological circumstances: (i) for Class‐I amplitude‐versus‐angle and ‐frequency, which corresponds to well‐compacted reservoirs having Class‐I amplitude‐versus‐offset characteristic, the root‐mean‐square amplitude at near offset is boosted at high frequency, whereas seismic energy at far offset is concentrated at low frequency; (ii) for Class‐II amplitude‐versus‐angle and ‐frequency, which corresponds to moderately compacted reservoirs having Class‐II amplitude‐versus‐offset characteristic, the weak seismic amplitude might exhibit a phase‐reversal trend, hence distorting both the seismic waveform and energy distribution; (iii) for Class‐III amplitude‐versus‐angle and ‐frequency, which corresponds to unconsolidated reservoir having Class‐III amplitude‐versus‐offset characteristic, the mesoscopic fluid flow does not exercise an appreciable effect on the seismic waveforms, but there exists a non‐negligible amplitude decay compared with the elastic seismic responses based on the Zoeppritz equation.     

Probability Data Screening Method in Airgun Signal Processing Application

The signal excited by the airgun source is weak, and is easily affected by human motion noise, instrument failure, and earthquake and blasting events, resulting in insufficient utilization of the amplitude information of the airgun signal. The effective removal of interference and the preservation of true amplitude information of the signal is difficult in airgun signal processing. Based on the randomness of noise and the highly repetitive characteristics of airgun signals, we propose probability data screening method. The airgun data from experiments conducted in the Ansha Reservoir and Shanmei Reservoir in Fujian Province in June, 2017 are taken as the research object to assess the effect in practical applications. The results show that the probability data screening method can automatically reject multiple interferences and effectively preserve the amplitude information of the signal by screening out large amplitude records in appropriate proportions. Compared with direct linear superposition, the probability-related linear superposition method can effectively reduce the impact of abnormal interference, and significantly improve the quality of the observed data.     

利用振幅谱差识别水淹层的变化

储层在长期水驱前后,其中的流体及储层本身会发生变化,导致速度和密度的变化,这一变化为应用四维地震监测油藏的变化提供了依据.本文基于平面波入射水平层状介质,推导出了用振幅谱差（四维振幅谱差）预测油藏变化的公式,并给出数值模拟的结果.理论计算表明,不同程度水驱和不同层位发生水淹其振幅谱差呈现明显的不同,从而在理论上证实了用振幅谱差预测油藏油水变化的可能.这为实际工作中利用振幅谱差预测地下油水变化奠定了理论基础.     

青海东部地震波参数的分析

以青海东部5个台站（湟源、西宁、乐都、大武、门源）十几年的地震观测资料为基础,分析震前地震波波速比、振幅比、S波衰减率、尾波持续时间的异常,并提取了异常指标为地震预报提供客观依据。