Rayleigh waves normally incident at a continental boundary

Abstract

S U M M A R Y Some results of a study of the propagation of monochromatic Rayleigh waves normally incident on the western ocean-continent boundary of the Iberian Peninsula are described. This seismological problem is modelled in two dimensions using the finite element method for periods in the range of 1.5 to 60.0s. The following results for ocean-continent direction of propagation are presented: (i) the estimate of the reflected and transmitted wavefields; (ii) the phase velocity curves for the fundamental mode in the transition zone; (iii) the transmission and reflection coefficients; and (iv) the seismic energy distribution for transmitted and reflected modes. Experimental data from P O R T 0 (PTO), a continental station, and PONTA DELGADA (PDA), an oceanic station, were compared to ascertain the effect on Rayleigh wave propagation across the continental margin. Comparison of the experimental amplitude ratios and transmission factor suggests a thickness of about 4 km for the sediment layer in the western oceanic zone of the Iberian Peninsula.

Review of the methodology for computation of transmission and reflection coefficients for the surface waves propagated through a vertical contact

“…The continuous line denotes the obtained results after the application of the proposed method, to the oceanic earth model (Table 4), proposed in this study to achieve the best fit possible with the observed data, and the continental earth model (Table 3) derived from previous models [1,2] ocean-continent boundary, existing between the Atlantic Ocean and the Iberian Peninsula. The dashed line denotes the results obtained after application of the simple method proposed in this paper, to the earth models proposed by Fitas and Mendes-Victor [4], listed in Tables 1 and 2, for the oceanic-continent boundary (assumed as a vertical contact) existing between the Atlantic Ocean and the Iberian Peninsula. This computed curve using this simple method (dashed line) is closer to the Rayleigh-wave transmission coefficients than the computed by the more sophisticated method based on the finite elements analysis [4].…”

“…The dashed line denotes the results obtained after application of the simple method proposed in this paper, to the earth models proposed by Fitas and Mendes-Victor [4], listed in Tables 1 and 2, for the oceanic-continent boundary (assumed as a vertical contact) existing between the Atlantic Ocean and the Iberian Peninsula. This computed curve using this simple method (dashed line) is closer to the Rayleigh-wave transmission coefficients than the computed by the more sophisticated method based on the finite elements analysis [4]. Therefore, the proposed simple method is shown as ef f icient as the sophisticated method, because the results given by both methods are very close and, probably, closer than the experimental error occurred in the calculation of the observed transmission and reflection coefficients.…”

“…In order to show the ef f iciency of the method proposed in this paper, firstly, the results of this method are compared with the results obtained by Fitas and Mendes-Victor [4], which used a more sophisticate method based on f inite element analysis. Figure 3 shows the transmission coefficients of Rayleigh wave for the (Table 3), based on previous earth models obtained for the Iberian Peninsula by Corchete et al [1,2].…”

“…where I (1) kL and I (1) kR , I (2) kR , I (3) kR , I (4) kR are the energy integrals for Love and Rayleigh waves listed and proved by Keilis-Borok [5].…”

“…This method will be very briefly described and compared with the more sophisticate method used by Fitas and Mendes-Victor [4] to obtain the transmission coefficients of the Rayleigh wave for the ocean-continent boundary, existing between the Atlantic Ocean and the Iberian Peninsula. The simple method will be shown as efficient as the more sophisticate method, computing a theoretical curve as close as possible to the observed data (the transmission coefficients of Rayleigh wave, measured by Fitas and Mendes-Victor [4] for this continent-ocean boundary). Thus, the goal of this paper is to show the validity and reliability of the simple method proposed by KeilisBorok [5] to be applied in a great variety of real problems, in which a vertical contact between two layered media is involved.…”