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

Philippe Rosset, Wyss Max

Acta Geophysica

2023

Vol. 71, no. 1

293--307

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.

Seismic landslide hazard assessment of central seismic gap region of Himalaya for a Mw 8.5 scenario event

Nayek Partha Sarathi, Gade Maheshreddy

Acta Geophysica

2021

Vol. 69, no. 3

747--759

In this study, seismic landslide hazard analysis is performed for central seismic gap (CSG) region of Himalaya for a future scenario earthquake of magnitude (Mw) 8.5. Initially, PGA values are estimated by using stochastic fnite fault seismological model. Further, the PGA values along with slope displacement prediction equation are used to estimate the Newmark’s sliding displacement. Monte Carlo simulations are performed by considering uncertainties in the material properties. Finally, the hazard map in terms of the probability of slope displacement (DN) value exceeding the threshold values of 5 cm is presented. The probability value varies between 0.1 and 1 and high probability in higher Himalayas highlights the possibility of huge number of co-seismic landslides in this region. The developed seismic landslide hazard map will help local authorities and planners with tools for assessing the seismic landslide risk associated with the use of land and taking necessary measures to minimize the damages.