Estimation of S-Wave Velocity Profiles at Lima City, Peru Using Microtremor Arrays

Abstract

Microtremor exploration was performed around seismic recording stations at five sites in Lima city, Peru in order to know the site amplification at these sites. The Spatial Autocorrelation (SPAC) method was applied to determine the observed phase velocity dispersion curve, which was subsequently inverted in order to estimate the 1-D S-wave velocity structure. From these results, the theoretical amplification factor was calculated to evaluate the site effect at each site. S-wave velocity profiles at alluvial gravel sites have S-wave velocities ranging from ∼500 to ∼1500 m/s which gradually increase with depth, while Vs profiles at sites located on fine alluvial material such as sand and silt have Swave velocities that vary between ∼200 and ∼500 m/s. The site responses of all Vs profiles show relatively high amplification levels at frequencies larger than 3 Hz. The average transfer function was calculated to make a comparison with values within the existing amplification map of Lima city. These calculations agreed with the proposed site amplification ranges.

Site dominant frequencies in Lima, Peru, by h/v spectral ratio of seismic records

“…Towards the center of Metropolitan Lima, 𝑓 𝑑 values tend to increase or to be unidentifiable due to either flat or jagged H/V spectral shapes. These areas are characterized by surficial gravel deposits (conglomerate) whose dominant peaks are expected at frequencies above 3 Hz ( [22], [23]).…”

Seismic analysis of underground structures: Influence of the soil type, the relative stiffness and seismic intensity

“…The soil properties for the three soil profiles are presented in Table 1. The stratified soil properties are based on the work of Quispe et al [15] which show the variation of shear wave velocity with depth at several points in Lima. The nonlinear and inelastic behavior of the soil subjected to cyclic loading was modeled using the sig3 hysteretic damping model of FLAC [14], which defines the backbone curve using three parameters and employs the Masing rules [16] to develop the hysteresis loops.…”