Journal of Earthquake and Tsunami

In this study, a pipe-soil finite element analysis model was built using the shaking table test results of buried pipelines that were achieved through longitudinal multipoint excitation and multipoint excitation under different seismic intensities, so as to numerically simulate the seismic response of buried pipelines under longitudinal multipoint excitation and multipoint excitation under different seismic intensities. As indicated by the result of this study, the numerical calculations and the shaking table test findings in terms of long-distance oil and gas pipelines under longitudinal multipoint stimulation were well consistent, such that the validity of both sets of results was verified. The peak pipe stresses during the multipoint excitation under different seismic intensities declined by 13.8% to 30.9% compared with case 2 longitudinal multipoint stimulation. The acceleration of the pipe and the soil was reduced rapidly as the measuring point moved farther away from the pipe’s leftmost distance. The displacement variation of the oil and gas pipelines under longitudinal multipoint excitation suggested that the soil displacement was increased with the length of the monitoring point from the bottom of the soil box for different elevations of the same section. The soil displacement declined notably for the same stretch at the identical elevation with the reduction of seismic intensity. The findings of this study can lay a basis for in-depth research on the effect of multipoint stimulation with different seismic powers on the seismic response of underground pipes.

One of the important factors in the amplification of seismic waves arriving the ground surface is site effects. Site effects, known as topographic irregularities, lead to seismic wave scattering, and this phenomenon can amplify or reduce the displacement recorded in different parts of a site. Therefore, it is necessary to investigate these effects for an accurate evaluation of the dynamic response of the structures built on these sites. One of the topics that has been given little attention is the interaction effects of topographic irregularities on each other’s dynamic responses. Using the three-dimensional boundary element method (3D-BEM) in the frequency domain, this study investigated the dynamic response of the site with canyons and hills adjacent to each other at different intervals and under SH seismic waves with different angles and dimensionless frequencies and with the hill in different geometries (semi-elliptical, triangular, semi-circular). The obtained results indicated that parts of the canyon that are adjacent to the hill underwent the greatest amplification, especially when the distance between the canyon and the hill is small. It was also found that the incident angle of the waves is one of the important parameters in the obtained displacement pattern on the site. Although the wave hit the canyon-hill site vertically, the results revealed that an asymmetric displacement pattern was experienced on the dynamic response of the site due to the phenomenon of amplification of seismic wave dispersion.

This work investigates the scattering of antiplane shear waves by tunnel in inhomogeneous half-space. The inhomogeneity of the medium is reflected in that the shear modulus is a two-dimensional function. Based on the complex function method, the analytical expressions of wave fields are obtained. The unknown coefficients can be obtained by boundary conditions. In the numerical example, the displacement amplitude of the horizontal surface and the dynamic response of lining structure are discussed. The results show that the inhomogeneous parameters, the reference wave numbers and the positions have obvious effects on the displacement amplitude and the dynamic response.

A new method is presented that simulates nonstationary multipoint earthquake accelerograms at local field points, when the observed ground motions are specified at several locations. This process effectively avoids the stochastic decomposition of the spectral matrix. In addition, it does not use the target spectrum and spatial coherence function to define the information of each point. First, the observed ground motions are reconstructed using an autoregressive model. Second, a new cross-regressive model is proposed based on the formulation of the auto-regressive model. The cross-regressive model can reconstruct different observed ground motions by using recordings from any nearby area. To consider the nonstationary characteristics and spatial coherence, the ground motions of unobserved points between two observed points can be generated using an interpolation algorithm. This new method simulates the ground motions of target points in the Chiba array using partially observed earthquake accelerograms. The simulated earthquake accelerograms satisfy the nonstationary characteristics and spatial coherence of the Chiba array. This study is promising for engineering applications and hazard analyses.

This paper presents the steel tunnel–sand–pile interaction (TSPI) response under scaled (0.05g and 0.1g) seismic excitations (Kobe and Loma Prieta) and sinusoidal wave (frequencies of 1, 5, and 7Hz) along with the sand relative densities of 48% and 80%. For this reason, a scaled shake table test was performed in the laboratory, and the 3D numerical analysis was performed by the Plaxis for the simulation. No joint was considered along the length of the tunnel to avoid complexity. In most cases, the excess pore pressure ratio exceeds the unit value at bottom and top locations of the TSPI model to inform the occurrence of liquefaction. Maximum lateral and translational displacements of the tunnel were found to be 143mm and 72mm, respectively, at the crown. In addition, the maximum vertical translation of sand and root mean square (RMS) value of the pile strain were obtained to be 61mm and 20$\mu$m/m, respectively. However, close variations of numerical and experimental studies may convince the accuracy of the simulation. By the way, it has a scope to enhance this study in the future by varying the geometry of the TSPI model.

Probabilistic seismic hazard analysis (PSHA) has become a fundamental tool in assessing seismic hazards and for estimating seismic design and seismic safety evaluation of ground motions. This report describes a study to test and verify the numerical approaches and software used in PSHA on Semnan, one of the important cities of Iran country. The geological and seismological data are integrated into a probabilistic seismic hazard model for the region. Historical and instrumental earthquake data, geology, tectonics, fault activity, and seismic source models associated with seismic events are taken into account. A probabilistic approach within a logic-tree framework is used to calculate seismic hazard for Semnan. The results were also displayed in terms of uniform hazard spectra for rock sites for return periods of 100, 475 and 2475 years, which is deemed appropriate for structural design standards in the Iran building code. As the results of this study have been displayed on the map for different return periods and different natural periods, it can provide the basis for the preparation of new seismic risk maps.