Amplitude-dependent effects of longitudinal seismic wave propagation in the interhole space

Field investigations of the amplitude dependence of the P wave velocity in dry and water-saturated rocks are carried out in the space between two shallow boreholes. The seismic wave velocity nonlinearly varies with the strain amplitude in the range ～(4–50) × 10^?8. The pattern of the velocity variation with amplitude depends on the pulse propagation direction. In dry and partially water-saturated rocks, the wave velocity decreases by 1.5% with the amplitude increasing within the range mentioned above and increases by 0.4% in completely water-saturated rocks (with an accuracy of up to 0.1%). Amplitude variations within a closed cycle (A _min … → A _max … → A _min) lead to hysteresis in the V _p (A _min-max-min) dependence (i.e., the ascending and descending branches of the curve do not coincide). If the hysteretic loop is not closed, the residual velocity component ΔV _p (A) is present. This effect is observed in dry and weakly saturated rocks. In a completely saturated rock, hysteresis of the velocity dependence is absent; the ascending and descending amplitude branches coincide. It is suggested that the amplitude characteristics and their hysteresis can be used in the future as an additional criterion for the differentiation of rocks by their fluid saturation.     

Dynamic microplasticity manifestation in consolidated sandstone in the acoustical frequency range

Microplasticity manifestations caused by acoustic wave in the frequency range of about 4.5 kHz–7.0 kHz are detected in consolidated artificial sandstone. Equipment was tested by means of comparison of data obtained for a standard material (aluminium) and sandstone. Microplasticity manifestations in acoustic records are present in the form of ladder‐like changes in the amplitude course. The stress plateaus in the acoustic trace interrupt the amplitude course, transform the wavefront, and shift the arrival time along the time axis. Microplasticity contribution to the acoustic record changes with the increase in the strain amplitude value. The combined elastic–microplastic process conditions the wavefront steepness and its duration. Stress plateaus exert influence on the waveform and, accordingly, on pulse frequency response. These results confirm the earlier data obtained for weakly consolidated rock. This contribution to wave propagation physics can be useful in solving applied problems in material science, seismic prospecting, diagnostics, etc.     

Strain amplitude-dependent attenuation of P and S waves in dry and water-saturated sandstone under confining pressure

The dependence of P- and S-wave attenuation on strain amplitude and frequency has been studied experimentally in dry and water-saturated sandstone samples under a confining pressure of 20 MPa. Attenuation of P and S reflections was measured at a frequency of 1 MHz in a strain range of ε ～(0.3?2.0) × 10⁶. The measured P-wave attenuation (Q_P^?1) in dry sandstone and S-wave attenuation (Q_S^?1) in dry and saturated samples turned out to be inversely proportional to strain amplitude while Q_P^?1 in saturated sandstone showed no strain dependence. The frequency-dependent attenuation spectra in dry and saturated sandstone differed considerably in S waves but were generally similar for P reflections. Strain amplitude variations were found out to influence the frequency dependence of attenuation and to shift the relaxation spectra of S waves toward high frequencies relative to those of P waves. As strain increased, the S-wave attenuation peak in saturated sandstone became notably (to 40%) narrower. The unusual strain amplitude-dependent behavior of attenuation may be due to joint action of viscoelastic and microplastic mechanisms. The reported results may be useful for improving geological interpretation of acoustic and seismic data.     

Attenuation of coda waves and Q_c value beneath the Chengdu telemetered seismic network

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基于ArcGIS的中温带不同天气类型点太阳辐射分析——以佳木斯市辖区为例

考虑天气情况对入射太阳辐射的影响,研究和分析日照时数、天气类型和辐射参数的关系,并将散射模型、透射率和散射比例与4种常用天气类型相对应。以佳木斯市辖区为例,采用ArcGIS的点太阳辐射分析批处理工具,对佳木斯辐射台站进行日入射太阳辐射分析。通过将默认情况和天气类型两种模拟结果与辐射台站的实测值进行分析和验证,获得两者的相关性R2分别为0.573 4和0.899 5。研究结果表明按不同天气类型进行中温带地区点太阳辐射分析的方法切实可行,并获得更好的点日太阳辐射模拟效果,其有利于研究不同天气类型下物理和生物过程模型所受到的太阳辐射影响。     

基于改进的MT-CLIM模型的中高纬低山丘陵区太阳辐射模拟——以小兴安岭为例

将DEM、坡度和坡向作为地形因子,基于ENVI/IDL编写MT-CLIM模型批量处理程序,使用改进MTCLIM模型对小兴安岭地区的地面气象台站进行太阳辐射模拟,并将模拟结果分别与辐射台站实测数据和二次趋势面统计模型进行验证。研究结果表明:从整年上,其与辐射台站的拟合精度R2为0.813 3,其中,夏季模拟太阳辐射日值拟合精度偏低,而其与二次趋势面统计模型拟合精度R2值范围为0.571 3~0.793 3;采用改进的MT-CLIM模型模拟较大区域的太阳辐射,比统计模型具有更好的普适性和高效性,能获得较好的中高纬低山丘陵区模拟效果,且为森林生态过程模型的输入参数研究提供依据。     

Characteristics of fault rocks and paleo-earthquake source along the Koktokay-Ertai fault zone,Xinjiang,China

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Dynamic microplasticity manifestation in consolidated sandstone in the acoustical frequency range

Microplasticity manifestations caused by acoustical wave in the frequency range of about 4.5 kHz–7.0 kHz are detected in consolidated artificial sandstone. Equipment was tested by means of comparison of data obtained for a standard material (aluminium) and sandstone. Microplasticity manifestations in acoustic records are present in the form of the ladder‐like changes in the amplitude course. The stress plateaus in the acoustic trace interrupt the amplitude course, transform the wavefront, and shift the arrival time along the time axis. Microplasticity contribution to the acoustic record changes with the increase in the strain amplitude value. The combined elastic–microplastic process conditions the wavefront steepness and its duration. Stress plateaus exert influence on the waveform and, accordingly, on pulse frequency response. These results confirm the earlier data obtained for weakly consolidated rock. This contribution to wave propagation physics can be useful in solving applied problems, as, for instance, the reservoir properties prediction by means of wave attenuation in acoustic logging and seismic prospecting.