Abstract

BONIVE, Francisco; BEAUPERTHUY, Luis; MONTILLA, Américo  and  ROJAS, Jorge. A comparison of the cortical structure using dynamic mean properties of Cumaná and Cumanacoa cities, Sucre state, Venezuela. Rev. Fac. Ing. UCV [online]. 2011, vol.26, n.2, pp.27-32. ISSN 0798-4065.

In this work we evaluate the cortical structure derived of dynamical properties of the cities Cumaná and Cumanacoa, Suﾭcre state, Venezuela. With this goal, spectral curves of frequency (H/V) were obtained using the JSESAME (ECU. 2000) program in the plots of environmental noise. We tried to fit with method of least squares, these curves to those obtained by applying the Nakamura model for ground microtremors, and the used equation was a corrected expression for S wave multireflection in parallel layers, which depends on the shallow crust model parameters (silt thickness, silt and basement S wave velocities, substrate and basement densities quotient, frequency, background noise, and high frequencies extinction). The families of curves linked to the different shallow crust models were obtained by a random approach, the phenotypic genetic algorithms. The solutions have two possible ranks of depth, a shallow one and a deep one, and this fact looks to depend on the frequency rank where the resonance picks appear. According to the results, we can state that the substrate thickness is significantly smaller at Cumanacoa than at Cumaná, which can be appreciated in both regimes average as the quantity of shallow solutions confronted with the deep ones: 95% to 35% in Cumanacoa and 86% to 82% in Cumaná. On the other hand, the extinction and the background noise are smaller at Cumanacoa than at Cumaná. The S velocities at the silt and at the basement, as well as the quotient between the respective densities are practically the same in both cities.

Keywords : Effect; microtremor; Nakamura’s Method; Seismic microzonation; Phenotypic Genetic Algorithms.