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Seismic microzonation study for two mining cities in the SW of Kyrgyzstan

Philippe Rosset, Wyss Max

Acta Geophysica

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2023

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Vol. 71, no. 1

293--307

EN

Kyrgyzstan is an earthquake-prone country at the border of the Pamir Thrust, north of the active shortening structure of the Pamir Mountains and the intra-continental mountain belt of the Tian Shan further north. The region has had several M7+damaging earthquakes, which have killed thousands of people. In the West, the country is cut through by the 700-km long NW–SE Talas-Fergana active strike-slip fault system, where no major earthquakes have been observed in the last 250 years even though paleoseismic studies show the potential to produce M7.0+events. This study is the second part of a project to estimate the potential damage and losses on residential buildings as well as critical infrastructures in the case of a large earthquake in the two mining towns of Kadamjay and Aidarken in the SW of Kyrgyzstan. Microtremors were recorded on 82 sites and analyzed with the Horizontal-to-Vertical Spectral Ratio (HVSR) method. For each site, we estimate the average frequency of the clearest peak and its amplitude in the HVSR spectra to produce microzonation maps, in terms of response frequency. We further used these data for the calculation of ground shaking using a set of six seismic scenarios based on the known faults around the two towns. This approach has proved to be efficient in a country where the resources and available data are limited and when the time of investigation is short. The Kadamjay and Aidarken cities have been divided into different zones with specific predominant resonance frequency ranges, which information is useful for risk analysis, mitigation and buildings retrofit. In Kadamjay, three regions dominate which are related to the history of alluvial deposition in a series of terraces. The more elevated terrace could be the place of seismic site amplification. Aidarkan is much more homogenous in terms of thickness and type of alluvial deposits.

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Seismic ground response analyses at an international airport in northern Italy by using a stochastic-based

Bozzoni Francesca, Ozcebe Ali Güney, Balia Andrea, Lai Carlo Giovanni, Borzi Barbara, Nascimbene Roberto, Ippoliti Lucia, Berardi Simona, Trombetti Marco, Moroni Claudio

Journal of Theoretical and Applied Mechanics

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2020

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Vol. 58 nr 2

499--511

EN

Airports play a crucial role in mitigation of seismic-induced disasters, being key elements in rescue operations after an earthquake. Under earthquake loading, various airport compo- nents can be damaged because of the ground shaking. It is well known that seismic ampli- fication of ground motion at the surface is strongly influenced by geotechnical properties of the soil deposits. In this paper, the spatial variability of ground amplification is assessed with reference to an international airport in Northern Italy. Homogeneous zones from a seismic geotechnical viewpoint were identified at the airport and, for each zone, stochastic ground response analyses carried out.

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Estimation of Seismic Site Coefficient and Seismic Microzonation of Imphal City, India, Using the Probabilistic Approach

Pallav K., Raghukanth S. T. G., Singh K. D.

Acta Geophysica

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2015

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Vol. 63, no. 5

1339--1367

EN

Seismic site coefficients (Fs) for Imphal city have been estimated based on 700 synthetically generated earthquake time histories through stochastic finite fault method, considering various combinations of magnitudes and fault distances that may affect Imphal city. Seismic hazard curves and Uniform Hazard Response Spectra (UHRS) are presented for Imphal city. Fs have been estimated based on site response analyses through SHAKE-91 for a period range of engineering interest (PGA to 3.0 s), for 5% damping. Fs were multiplied by UHRS values to obtain surface level spectral acceleration with 2 and 10% probability of exceedance in 50 year (~2500 and ~500 year) return period. Comparison between predicted mean surface level response spectra and IS-1893 code shows that spectral acceleration value is higher for longer periods (i.e., > 1.0 s), for ~500 year return period, and lower for periods shorter than 0.2 s for ~2500 year return period.

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Computation of ground motion amplification in Kolkata megacity (India) using finite-difference method for seismic microzonation

Shiuly A, Kumar V, Narayan J.P.

Acta Geophysica

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2014

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Vol. 62, no. 3

425--450

EN

This paper presents the ground motion amplification scenario along with fundamental frequency (F0) of sedimentary deposit for the seismic microzonation of Kolkata City, situated on the world’s largest delta island with very soft soil deposit. A 4th order accurate SH-wave viscoelastic finite-difference algorithm is used for computation of response of 1D model for each borehole location. Different maps, such as for F0, amplification at F0, average spectral amplification (ASA) in the different frequency bandwidth of earthquake engineering interest are developed for a variety of end-users communities. The obtained ASA of the order of 3-6 at most of the borehole locations in a frequency range of 0.2510.0 Hz reveals that Kolkata City may suffer severe damage even during a moderate earthquake. Further, unexpected severe damage to collapse of multi-storey buildings may occur in localities near Hoogly River and Salt Lake area due to double resonance effects during distant large earthquakes.