Effect of a simple mountain range on underground seismic motion

Abstract

The influence of a simple mountain range on seismic ground motion is studied. A two-dimensional model of the medium and vertically incident plane SH-waves are considered. Attention is devoted not only l o the wavefield along the Earth's surface, but also within the medium. The wavefield is computed in two steps: ( I ) the computation of the impulse response by the finite-difference method, (2) the computation of the response t o a time variation of the incident wave. approximately corresponding t o a 'hundred-yeai-' local earthquake a ( the sitc. Numerical results (the impulse 1-esponse. the transfer function, the accelerograms, and their spectra) indicate strong spatial variability of the wavefield due to the topographical anomaly. The differences as large as 100 per cent in the peak amplitudes of the accelerograms, and of the order of 5 Hz in their predominant frequencies, at closely (-200 m) spaccd internal points of the medium have been found. Attention is focused also on the effect of causal absorption. Even unrealistically strong absorption seems to be unable t o reduce significantly the spatial variability of the ground niotion. caused by the topography. A variability like this. implying the occurrence of underground differential strains, might be of engineering inipoi-lance in the antiseismic desigti of underground structures (tunnels, for example) in mountainous seismic I-egions. The groundmotion variability along the surface of the mountain is considerably smaller than within the medium.

Estimation of topographical effects at Narni ridge (Central Italy): comparisons between experimental results and numerical modelling

“…The methods more widely used are the finite difference method (Boore 1972;Zahradnlk and Urban 1984), the finite element method (Smith 1975), the integral equation method (Sills 1978), the boundary element methods (Sanchez-Sesma et al 1982), the discrete wave-number methods (Bouchon 1973;Bard 1982) and the spectral element methods (Faccioli et al 1997;Komatitsch and Vilotte 1998). In general the common result of modelling, if compared with experimental methods, is the underestimation of the amplification factors if compared to those obtained by experimental data.…”

Full Seismic Waveform Modelling and Inversion

“…Applications of the vacuum formulation can be found, for instance, in Zahradník & Urban (1984), Zahradník et al (1993), Ohminato & Chouet (1997) and Bohlen & Saenger (2006). Since this is intended to approximate a vacuum, the method is commonly referred to as vacuum formulation.…”

Incident P and SV wave scattering effects under different canyon topographic and geological conditions

“…The physical explanation for this is that the wave in the far field can be approximately represented by the superposition of plane harmonic waves. Based on this recognition and taking the multiple wavenumbers into account, the general form of the wave propagation function in the twodimensional dynamic infinite element can be expressed as ( 5 ) Pq(<) = e-a*5(cle-iBir + c2e-i"2r) (q = 1, 2, ... , 6 )…”