We propose a method for mOdeling azimuthal AVO responses from a fractured i reflector. The method calculates the integrated reflected wavetrains, and the wavetrains contain elastodynamic information including the con...We propose a method for mOdeling azimuthal AVO responses from a fractured i reflector. The method calculates the integrated reflected wavetrains, and the wavetrains contain elastodynamic information including the contrast in impedance and anelasticity i across interfaces, the intemal anisotropic propagation, the dispersion and attenuation along i the wave path, and tuning and interference. The results suggest that for large angles of incidence, the velocity dispersion and attenuation increase the amplitudes of PP waves from the top and decrease those from the bottom. For azimuthal responses at specific angles of incidence, the reflected wavetrains of PP waves tend to have longer duration with increasing azimuth. In contrast, model-converted PSV and PSH reflections show stable azimuthal features and are less affected by the reflector thickness. The amplitudes of PSV reflections increase with increasing azimuth; moreover, the waves have no reflection energy at 0° and 90° azimuth and maximum amplitude at 45° azimuth.展开更多
Rupture directivity effect causes spatial variation in strong ground motion parameters. It causes difference between the strike- normal （V.） and strike-parallel （Vp） components of horizontal ground motion amplitud...Rupture directivity effect causes spatial variation in strong ground motion parameters. It causes difference between the strike- normal （V.） and strike-parallel （Vp） components of horizontal ground motion amplitudes. These variations become significant for strong ground motion velocity and the authors have developed a modification to define directivity effect factor to account for the effect of rupture directivity in empirical velocity attenuation relations which are based on modeling Silakhor earthquake, using finite element method by ANSYS. The ground motion parameters that are modified include ratio of Vn/Vp component of horizontal velocity and Vn component to average horizontal velocity （V）. The ratio of Vn to Vp is large in both the forward directivity direction, where velocity is larger, and in the backward directivity direction, where velocity is smaller. Therefore the authors expected that the Vn/Vp was mainly controlled by directivity angle. Also the variation of fault normal velocity to average horizontal velocity ratio by directivity angle （0） is defined from earthquake modeling. It shows Vn/V is controlled by directivity angle, distance between the site, epicenter and rupture length. This ratio has the same trend in Silakhor earthquake strong ground velocity data. In this paper the equation for Vn/Vp variations by directivity angle is recommended. The authors used Somervill et al. （1997） directivity model parameters as （R/L） cos2 ~ to define directivity effect on Vn/V ratio and therefore directivity factor is determined to account in near field empirical strong ground velocity attenuation relationships.展开更多
基金sponsored by the National Natural Science Foundation of China(under Grant Nos.41404090 and U1262208
文摘We propose a method for mOdeling azimuthal AVO responses from a fractured i reflector. The method calculates the integrated reflected wavetrains, and the wavetrains contain elastodynamic information including the contrast in impedance and anelasticity i across interfaces, the intemal anisotropic propagation, the dispersion and attenuation along i the wave path, and tuning and interference. The results suggest that for large angles of incidence, the velocity dispersion and attenuation increase the amplitudes of PP waves from the top and decrease those from the bottom. For azimuthal responses at specific angles of incidence, the reflected wavetrains of PP waves tend to have longer duration with increasing azimuth. In contrast, model-converted PSV and PSH reflections show stable azimuthal features and are less affected by the reflector thickness. The amplitudes of PSV reflections increase with increasing azimuth; moreover, the waves have no reflection energy at 0° and 90° azimuth and maximum amplitude at 45° azimuth.
文摘Rupture directivity effect causes spatial variation in strong ground motion parameters. It causes difference between the strike- normal （V.） and strike-parallel （Vp） components of horizontal ground motion amplitudes. These variations become significant for strong ground motion velocity and the authors have developed a modification to define directivity effect factor to account for the effect of rupture directivity in empirical velocity attenuation relations which are based on modeling Silakhor earthquake, using finite element method by ANSYS. The ground motion parameters that are modified include ratio of Vn/Vp component of horizontal velocity and Vn component to average horizontal velocity （V）. The ratio of Vn to Vp is large in both the forward directivity direction, where velocity is larger, and in the backward directivity direction, where velocity is smaller. Therefore the authors expected that the Vn/Vp was mainly controlled by directivity angle. Also the variation of fault normal velocity to average horizontal velocity ratio by directivity angle （0） is defined from earthquake modeling. It shows Vn/V is controlled by directivity angle, distance between the site, epicenter and rupture length. This ratio has the same trend in Silakhor earthquake strong ground velocity data. In this paper the equation for Vn/Vp variations by directivity angle is recommended. The authors used Somervill et al. （1997） directivity model parameters as （R/L） cos2 ~ to define directivity effect on Vn/V ratio and therefore directivity factor is determined to account in near field empirical strong ground velocity attenuation relationships.
