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

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. [ABSTRACT FROM AUTHOR]