Seismic site effects in a deep alluvial basin: numerical analysis by the boundary element method

TL;DR

This paper uses the boundary element method to numerically analyze seismic site effects in Caracas, revealing amplification patterns, frequency dependencies, and validating results with microtremor recordings.

Contribution

It demonstrates the effectiveness of the boundary element method for analyzing seismic site effects in complex deep alluvial basins.

Findings

Maximum amplification factor of 25 in the basin

Site effects are frequency-dependent, occurring below 1 Hz and above 1 Hz

Numerical results agree well with microtremor data

Abstract

The main purpose of the paper is the numerical analysis of seismic site effects in Caracas (Venezuela). The analysis is performed considering the boundary element method in the frequency domain. A numerical model including a part of the local topography is considered, it involves a deep alluvial deposit on an elastic bedrock. The amplification of seismic motion (SH-waves, weak motion) is analyzed in terms of level, occurring frequency and location. In this specific site of Caracas, the amplification factor is found to reach a maximum value of 25. Site effects occur in the thickest part of the basin for low frequencies (below 1.0 Hz) and in two intermediate thinner areas for frequencies above 1.0 Hz. The influence of both incidence and shear wave velocities is also investigated. A comparison with microtremor recordings is presented afterwards. The results of both numerical and experimental approaches are in good agreement in terms of fundamental frequencies in the deepest part of the basin. The boundary element method appears to be a reliable and efficient approach for the analysis of seismic site effects.