Preliminary Analysis for Evaluation of Local Site Effects in Lima City, Peru from Ground Motion Data by Using the Spectral Inversion Method

Abstract

Effects of local site, propagation path and source in ground motion records observed in Lima, Peru, were separated by the spectral inversion method proposed by Iwata and Irikura (1986 [1], 1988 [2]) to examine the relation between local subsurface conditions and local site amplifications in a frequency range from 0.5 to 20 Hz. S-wave portions of accelerograms in horizontal components observed at 5 stations for 11 events along the Pacific coast of Lima city, Peru, were analyzed. The Q factor was obtained from our inversion results as frequency-dependent functionQS( f )= 80.4f0.63. In terms of local site effects, stations located on alluvial gravel deposits were likely to suffer amplification at frequencies larger than 4 Hz, while one station (CAL site) located on soft soil sediment has different behavior of amplification. We also compared our results with 1-D theoretical computation, observed standard spectral ratio and observed H/V spectra in previous studies, finding that site responses determined by different methods are similar. In addition, we analyzed the relationship between average S-wave velocity in the top 10 meters and the average site amplification factor in a frequency range between 0.5 Hz and 10.0 Hz, showing a good correlation between the two parameters. We also calculated the average transfer function (AvTF) to compare it with the existing amplification map for Lima city, and found that our calculations differed from this map.

Summary Report of the SATREPS Project on Earthquake and Tsunami Disaster Mitigation Technology in Peru

“…Group 1 studies seismic motion and geotechnical aspects through seismic and microtremor observations at the case study sites. Together with existing geological data and newly conducted borehole surveys, the soil amplification characteristics have been investigated [5][6][7].…”

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

“…Both PUCP and CER sites, which are located on alluvial gravel, show several peaks at frequencies above 3 Hz, corresponding to the site response of the Lima conglomerate. Using strong ground motion data, Quispe et al (2012) [14] reported that this deposit suffers from high amplification at frequencies larger than 4 Hz. The PUCP site shows a small bump between 1 and 2 Hz, which is also identified in the observed H/V spectral ratio of the microtremor data (Fig.…”