Attenuation of peak ground accelerations from the great Wenchuan earthquake

Over 800 accelerograms recorded by 272 ground-level stations during the Wenchuan earthquake are used to analyze the influence of rupture distance, local site conditions and azimuth on peak ground accelerations （PGAs）. To achieve a better understanding of the characteristics of ground motions, the spatial distributions of the EW, NS and UD components of PGAs are obtained. Comparisons between the EW and NS components, the fault-normal and fault-parallel components, and the vertical and horizontal components of PGAs are performed, and the regression formula of the vertical-to-horizontal ratio of PGAs is developed. The attenuation relationship of peak horizontal accelerations （PHAs） is compared with several contemporary attenuation relationships. In addition, an analysis of residuals is conducted to identify the potential effects of rupture distance, azimuth and site conditions on the observed values of PHAs. The analysis focuses on medium-hard soil site conditions, as they provided most of the data used in this study.

Geometric effects resulting from the asymmetry of dipping fault:Hanging wall/ footwall effects

Root-mean-square distance Drms with characteristic of weighted-average is introduced in this article firstly. Drms can be used to capture the general proximity of a site to a dipping fault plane comparing with the rupture distance Drup and the seismogenic distance Dseis. Then, using Drup, Dseis and Drms, the hanging wall/footwall effects on the peak ground acceleration (PGA) during the 1999 Chi-Chi earthquake are evaluated by regression analysis. The logarithm residual shows that the PGA on hanging wall is much greater than that on footwall at the same Drup or Dseis when the Drup or Dseis is used as site-to-source distance measure. In contrast, there is no significant difference between the PGA on hanging wall and that on footwall at the same Drms when Drms is used. This result confirms that the hanging wall/footwall effect is mainly a geometric effect caused by the asymmetry of dipping fault. Therefore, the hanging wall/footwall effect on the near-fault ground motions can be ignored in the future attenuation analysis if the root-mean-square distance Drms is used as the site-to-source distance measure.

Capillary bridges and capillary forces between two axisymmetric power-law particles

Capillary interactions are fundamentally important in many scientific and industrial fields. However, most existing models of the capillary bridges and capillary forces between two solids with a mediated liquid, are based on extremely simple geometrical configurations, such as sphere-plate, sphere-sphere, and plate-plate. The capillary bridge and capillary force between two axisymmetric power-law profile particles with a mediated constant-volume liquid are investigated in this study. A dimensionless method is adopted to calculate the capillary bridge shape between two power-law profile particles based on the Young-Laplace equation. The critical rupture criterion of the liquid bridge is shown in four forms that produce consistent results. It was found that the dimensionless rupture distance changes little when the shape index is larger than 2. The results show that the power-law index has a significant influence on the capillary force between two power-law particles. This is directly attributed to the different shape profiles of power-law particles with different indices. Effects of various other parameters such as ratio of the particle equivalent radii, liquid contact angle, liquid volume, and interparticle distance on the capillary force between two power-law particles are also examined.