Browsing by Author "Aguilar, Zenon"

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    Estimation of S-wave velocity profiles at Lima city, Peru using microtremor arrays
    (Fuji Technology Press, 2014) Quispe, Selene; Chimoto, Kosuke; Yamanaka, Hiroaki; Tavera, Hernando; Lazares, Fernando; Aguilar, Zenon
    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.
    Palabras clave:MicrotremorsS-wave velocity profilesSite response
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    Preliminary analysis for evaluation of local site effects in Lima city, Peru from ground motion data by using the spectral inversion method
    (Fuji Technology Press, 2013) Quispe, Selene; Yamanaka, Hiroaki; Aguilar, Zenon; Lazares, Fernando; Tavera, Hernando
    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 function QS( f) = 80.4 f 0.63. 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.
    Palabras clave:Lima CityLa MolinaCallao
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    Strong motion simulation of the M8.0 August 15, 2007, Pisco earthquake; effect of a multi-frequency rupture process
    (Journal of Disaster Research, 2013-03) Pulido, Nelson; Tavera, Hernando; Aguilar, Zenon; Nakai, Shoichi; Yamazaki, Fumio
    We investigated the broadband frequency (0.05-30 Hz) radiation characteristics of the August 15, 2007, Mw8.0 Pisco, Peru, earthquake by simulating the near-source strong ground motion recordings in Parcona city (PCN) and Lima city (NNA). A source model of this earthquake obtained from long-period teleseismic waveforms and InSar data shows two separate asperities, which is consistent with the observation of two distinct episodes of strong shaking in strong motion recordings. We constructed a source model that reproduces near-source records at low frequency (0.05-0.8 Hz) as well as high frequency (0.8-30 Hz) bands. Our results show that the aforementioned teleseismic source model is appropriate for simulating near-source low frequency ground motion. Our modeling of the PCN record in the broad-frequency band indicates that a very strong high frequency radiation event likely occurred near the hypocenter, which generated a large acceleration peak within the first episode of strong shaking at PCN. Using this “broadband frequency” source model we simulated the strong ground motion at Pisco city and obtained accelerations as large as 700 cm/s2 and velocities as high as 90 cm/s, respectively, which may explain the heavy damage occurring in the city.
    Palabras clave:Seismic riskEarthquakesTectonic plate