Site Amplification Analysis of Dushanbe City Area, Tajikistan to Support Seismic Microzonation

Abstract

Being a country exposed to strong seismicity, the estimation of seismic hazard in Tajikistan is essential for urbanized areas, such as the rapidly growing capital city Dushanbe. To ensure people’s safety and adequate construction work, a detailed seismic microzonation is the key to proper hazard planning. Existing estimations of seismic hazard date back to 1978; they are based on engineering geological investigations and observed macroseismic data. Thereupon relies the Tajik Building Code, which considers seismic intensities according to the Medvedev–Sponheuer–Karnik Scale, MSK-64. However, this code does not accurately account for soil types, which vary considerably in Dushanbe—not only by their nature, but also due to increasing anthropogenic influences. In this study, we performed a series of analyses based on microtremor array measurements, seismic refraction tomography, and instrumental data recording from permanent stations for standard spectral ration and from mobile seismic stations for the horizontal to vertical spectral ratio in order to provide a comprehensive full-cover microzonation of Dushanbe accounting for soil types. Our results identify several critical areas where major damage is likely to occur during strong earthquakes.

Assessment of Site Effects and Numerical Modeling of Seismic Ground Motion to Support Seismic Microzonation of Dushanbe City, Tajikistan

“…This allowed for a more accurate assessment of the site effects and determination of the PGA in the study area, contributing to more substantiated seismic microzonation and seismic hazard assessment. The results also confirmed the impact of strong seismic amplification due to local topographical and ground characteristics, in line with the conclusions of previous studies [11,34].…”

“…The second terrace is elevated by a 1-3 m step above the Varzob River floodplain and is overlaid by a loess cover ranging from 5 to 10 m in thickness. The third terrace, which gently slopes southwestward, is predominantly composed of loess strata 20-40 m thick and features a pronounced escarpment of 12-18 m leading down to the second terrace, as detailed in the study by Hakimov et al [34].…”

“…These data encompass five microtremor array measurements (MAM), nine seismic refraction tomography (SRT), five temporary seismic stations for SSR from earthquake data, 60 borehole data, and 175 measurements of HVSR (Table 2). All these data were integrated and presented on maps within a Geographic Information System (GIS) using a unified reference system, as detailed in the first part of our project by Hakimov et al [34].…”

“…The Quaternary loess is one of the most common types of deposit in the city and its surroundings, characterized by varying thickness and hydromechanical properties; clays, sands, and gravel are also encountered [48]. Recently, new data on the seismic microzonation of Dushanbe have been obtained, covering not only general geological conditions but also new geophysical data and records from a temporary seismic network [34].…”

Landslide Susceptibility Mapping in the Vrancea-Buzău Seismic Region, Southeast Romania

“…It provides a critical review of almost all relevant existing statistical methods. Generally, landslide studies are performed according to several hazard assessment models: expert or heuristic models, statistical models [22], statistical and geotechnical models [23,24], spatial multi-criteria evaluation (SMCE) [16], spatially explicit deep learning neural network models [25], machine learning models [26] and some of them also consider seismic microzonation models [27]. Regarding the landslide data input, it has been shown that the performance of a susceptibility model varies slightly after progressive updating and addition of landslide data over time [28].…”