The responses of two types of soft basins for incident SH, SV, P , and Rayleigh waves in a 2-D elastic half-space are investigated with special reference to the long duration of strong motions observed in Mexico City during the Michoacan, Mexico, earthquake of 1985. First, the difficulty for simple 1-D models to reproduce the later part of the accelerogram observed in Mexico City is shown. Then the effect of a 2-D deep basin structure of a relatively large scale (10 km wide and 1 km deep) and a moderate impedance ratio (2.5) is studied. The results show that surface waves generated at the edges of the basin are clearly propagating inside the basin back and forth. However, the increase in duration by these surface waves is 20 sec at most. Introducing another much softer layer inside the basin, we found that the calculated durations and envelop shapes become very similar to the observed ones because of the slowness of surface-wave propagation. These theoretical studies suggest that the exceptionally long duration observed in Mexico City might be caused by a strong, constructive interaction of soft-surface layers with a deep basin structure beneath the city.

A study on the response of a soft basin for incident S, P, and Rayleigh waves with special reference to the long duration observed in Mexico City

The responses of a semi-circular canyon for incident SH, SV, P , and Rayleigh waves in a two-dimensional elastic half-space are investigated in time domain as well as in frequency domain. The author proposes the discrete wavenumber boundary element method, in which the direct boundary element method is used with the discrete wavenumber Green's function. This combination achieves both the efficiency in computation and the flexibility for boundary configurations. First, the validity of the method is confirmed by comparing its results with published ones in frequency domain. Then time histories of seismic motion along the surface in and around the canyon are studied for incident SH, SV, P , and Rayleigh waves with the shape of a Ricker wavelet. In all cases, the diffracted waves called the creeping waves can be seen propagating inside the canyon with P - or S -wave velocity. For SV -wave incidence, Rayleigh waves generated at the edges of the canyon carry a significant portion of energy outward, while for SH -wave incidence the direct and reflected waves play a major role. It should be noted that the amplitude fluctuation in frequency domain does not always mean that in time domain because different arrival time of wavelets results in the fluctuation in spectral amplitude even if each wavelet propagates with the same shape and amplitude.

Time-domain response of a semi-circular canyon for incident SV, P, and Rayleigh waves calculated by the discrete wavenumber boundary element method

The data on the present degree of purity of chalcogenide glasses for fiber optics, on their methods of production and on the properties, which are essential for their actual application, are generalized. The content of limiting impurities in the best samples of chalcogenide glasses is 10–100 ppb wt.; of heterophase inclusions with size of about 100 nm is less than 103 cm−3. On the basis of chalcogenide glasses the multimode and single mode optical fibers are produced with technical and operation characteristics sufficient for a number of actual applications. The minimum optical losses of 12–14 dB/km at 3–5 µm are attained in the optical fiber from arsenic-sulfide glass. The level of losses in standard chalcogenide optical fibers is 50–300 dB/km in 2–9 µm spectral range. The factors, affecting the optical absorption of glasses and optical fibers, are analyzed, and the main directions in further development of chalcogenide glasses as the materials for fiber optics are considered.

High-purity chalcogenide glasses for fiber optics

http://users.ntua.gr/gbouck/downfiles/numerical_evaluation_of_slope_topography_effects.pdf

Numerical evaluation of slope topography effects on seismic ground motion

Connection machine simulation of ultrasonic wave propagation in materials III: The three-dimensional case

The effect of topography and subsurface inhomogeneity on surface motion is investigated in the case of incident SV waves Several types of topography, such as a cliff, a cliff with a soft layer and filled land, are considered Computations are made using a new method combining a particle model with a finite element method The accuracy of this method is discussed through comparisons with Wong's solutions, which are in good agreement It is found that the surface displacement is very much influenced by surface irregularities when the incident wavelengths are comparable to the size of the topographic features Rayleigh waves are strongly produced in the neighbourhoods of the slopes of a cliff and a cliff with a soft layer, the latter being a cliff adjacent to and covered at its foot by a soft layer Thus, a zone of large amplification takes place near a slope, combining incident SV waves and Rayleigh waves A large displacement also occurs at the upper corner of the slope In filled land, vertical and horizontal displacements are produced, which are 3 times larger than those at a distance The present results are considered to be significant from the viewpoint of engineering seismology

Effect of topography and subsurface inhomogeneities on seismic SV waves

High-speed, large-memory computers have made feasible accurate computer simulations of ultrasound in solids. The basic equations and models used for the simulations are presented, and some 400 results are outlined. The results are shown to be quite accurate by comparison with experiments. Current and possible future applications of the technique to NDT are discussed.

Computer simulation of ultrasonics in a solid

The effect of topography and subsurface inhomogeneity on surface motion is investigated in the case of Rayleigh waves. In the previous paper, the same effect was investigated in the case of SV waves. Several types of topography, such as cliffs both with and without a soft layer at the foot of the slope, are considered. Computations are made using a new hybrid method combining a particle model with a finite element method. In cases of harmonic Rayleigh waves, surface motions with amplitudes as large as 1.5 to 5 times the horizontal surface displacement of the incident Rayleigh waves are produced near the slope and the sloping interface. When a Rayleigh wave propagating through a hard single-layered ground encounters a sloping interface where hard ground and soft ground make contact with each other, Rayleigh waves having two different, phase velocities are produced and they correspond to the fundamental mode, and the first mode determined by Haskell's method. In addition, the transient response when Rayleigh waves propagate through the cliff is also simulated. Assuming the vertical component of the Tokachi-oki Earthquake (1968) measured on the surface to be a Rayleigh wave, the incident Rayleigh wave can be obtained by a Fourier synthesis of eigenfunctions of Rayleigh waves.

Kasaburo Harumi

Papers

Effect of topography and subsurface inhomogeneities on seismic SV waves

Computer simulation of ultrasonics in a solid

Computer simulation of ultrasonics in a solid

Effect of topography and subsurface inhomogeneity on seismic rayleigh waves

Surface motion of a layered medium having an irregular interface due to rayleigh waves