Abstract

Coherency and apparent velocity are two major functions which control the simulation of strong ground motion at multiple stations. In this paper, after a brief review of a method of generating time series inputs for any given set of n surface locations having space coordinates x_i and y_i (i = 1, 2, …, n), compatible with the observed wave propagation properties, we present some of the results obtained in a study of coherency and apparent velocity of several earthquakes recorded at -1 array. Based on data collected in the inner ring of -1 array (stations spaced from 100m to 400m), we studied: (i) the loss of coherency function γ_ij(d_ij^L, d_ij^T, f) for pairs of records obtained at stations i, j, as a continuous function of frequency f, and projected separation distances d_ij^L and d_ij^T in the longitudinal direction of preferential wave propagation and in the transverse direction, respectively; (ii) the apparent velocity V_app as a function of frequency f. In face of the regularity exhibited by the coherency function, an heuristic model with several parameters was assumed and parameter values are estimated for each earthquake using least square methods. No such regularity was observed in relation to apparent velocities. Preliminary conclusions of dependence of those two functions upon the geologic and seismotectonic characteristics of the -1 environment is analysed and a set of recommendations for engineering applications is briefly discussed. The paper concludes with the presentation of an example of simulation of ground motion using the above mentioned results.

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