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Quispe S.,Tokyo Institute of Technology | Yamanaka H.,Tokyo Institute of Technology | Aguilar Z.,Peruvian National University of Engineering | Lazares F.,Peruvian National University of Engineering | Tavera H.,Geophysical Institute of Peru IGP
Journal of Disaster Research | Year: 2013

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 Q S (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.

Pulido N.,Japan National Research Institute for Earth Science and Disaster Prevention | Tavera H.,Geophysical Institute of Peru IGP | Aguilar Z.,Peruvian National University of Engineering | Nakai S.,Chiba University | Yamazaki F.,Chiba University
Journal of Disaster Research | Year: 2013

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/s 2 and velocities as high as 90 cm/s, respectively, which may explain the heavy damage occurring in the city.

Adriano B.,Tohoku University | Mas E.,Tohoku University | Koshimura S.,Tohoku University | Fujii Y.,Japan Building Research Institute | And 3 more authors.
Journal of Disaster Research | Year: 2013

Within the framework of the project Enhancement of Earthquake and Tsunami Disaster Mitigation Technology in Peru (JST-JICA SATREPS), this study determines tsunami inundation mapping for the coastal area of Lima city, based on numerical modeling and two different tsunami seismic scenarios. Additionally, remote sensing data and geographic information system (GIS) analysis are incorporated in order to improve the accuracy of numerical modeling results. Moreover, tsunami impact is evaluated through application of a tsunami casualty index (TCI) using tsunami modeling results. Numerical results, in terms of maximum tsunami depth, show a maximum inundation height of 6 m and 15.8 m for a potential scenario (first source model) and for a past scenario (second source model), respectively. In terms of inundation area, the maximum extension is 1.3 km with a runup height of 5.3 m for the first scenario. The maximum extension is 2.1 km with a runup height of 11.4 m for the second scenario. The average TCI value obtained for the first scenario is 0.36 for the whole inundation domain. The second scenario gives a mean value of 0.64, where TCI equal to 1.00 represents the highest condition of risk. The results presented in this paper provide important information about understanding tsunami inundation features and, consequently, may be useful in designing an adequate tsunami evacuation plan for Lima city.

Quispe S.,Tokyo Institute of Technology | Chimoto K.,Tokyo Institute of Technology | Yamanaka H.,Tokyo Institute of Technology | Tavera H.,Geophysical Institute of Peru IGP | And 2 more authors.
Journal of Disaster Research | Year: 2014

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. © 2014 Fuji Technology Press. All rights reserved.

Agency: GTR | Branch: NERC | Program: | Phase: Research Grant | Award Amount: 51.99K | Year: 2014

The Peru-Chile subduction zone hosts many large earthquakes. A M8.8 earthquake occurred in northern Chile in 1877, and since then, no major event had re-ruptured the area prior to April 2014. The 500 km-long zone has therefore become known as the North Chile seismic gap. In late March 2014, many small to moderate earthquakes occurred within this gap. Activity generally migrated slightly northwards. On 2 April 2014, a M8.2 earthquake occurred in the northern part of the preceding cluster, followed by many aftershocks, including a M7.6 event. Aftershock activity continues and, since the rest of the area has not experienced a major earthquake for well over a century, another large event in the area in the near future or medium term cannot be ruled out. In order to measure aftershock activity in the area of the seismic gap that ruptured recently, in addition to any other events that may occur nearby, we propose to install seismometers in the Peruvian coastal region and also offshore Chile. There are two main reasons for doing this. Firstly, the extra networks will dramatically improve station coverage around the seismic gap area, enabling us to generate detailed models of the subduction zone. This will be of great benefit for future analyses of seismic activity in this earthquake-prone area. Secondly, our records of the ongoing seismic activity will enable us to locate aftershocks accurately and infer what type of faulting occurred. This will enable us to build up a very detailed picture of how post-earthquake processes relate to preceding large seismic events. We will also use satellite radar images to construct maps of how the surface of the Earth has moved as a result of the recent seismic activity. These deformation maps can be used in computer models to estimate the location and magnitude of slip that occurred on faults beneath the surface - for instance, on the subduction zone interface, where the mainshock occurred. Essentially we are using surface measurements to infer sub-surface processes. Results from the seismological and satellite components of our project will be integrated to give us an in-depth understanding of the properties and processes occurring in the North Chile seismic gap. For instance, we will look at the spatial relationship between the area that ruptures in major earthquakes and the location of foreshock/aftershock sequences. Another important issue is to identify areas on the subduction zone interface that have not yet slipped, and that could therefore rupture in major earthquakes in the future.

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