Investigation of seismic wave amplification characteristics by subsurface soil layers is important for seismic hazard assessment. In response, Kyrgyz Republic now requires the consideration of site conditions using averaged S-wave velocity over the top 30m of soil (Vs30) to improve national building code. In this study, we estimated shear wave velocity (Vs) structure at two sites in Naryn city, central Kyrgyz Republic, using Spatial Auto-correlation (SPAC) method with irregularly shaped microtremor arrays. On the other hand, single station microtremor data from 135 sites all over the city are used to obtain horizontal-to-vertical (HVSR) spectral ratios. The results of SPAC analysis indicate that the depth of engineering bedrock is shallower than 20 m at both sites. Averaged values of Vs30 obtained from the estimated structures show that both sites correspond to NEHRP site class C.
On the other hand, results from the recently proposed site classification method with microtremor H/V spectral ratio show that the site classes C and D are dominant with few exceptions of the class E in the target area.
This study clarified that the combined use of microtremor array data with single station data can be a powerful tool to investigate site classification for seismic microzonation and also suggested the necessity of further surveys in the area, focusing on shallower structure, i.e., the youngest fluvial sediment and loess.
Keywords: Microtremors, Shear Wave Velocity, SPAC Method, H/V Spectral Ratio Method.