Seismic Site Characterization involves the qualitative assessment of top-soil properties that have the capability of amplifying the generated earthquake ground motions. The geotechnical properties of topsoil refer to the top 30m subsurface profile which plays a vital role in seismic microzonation and Ground Response Analysis (GRA) studies. Among various geotechnical parameters, shear-wave velocity (Vs) of the top 30 m subsurface is mainly linked to seismic site characterization and amplification studies. The average shear-wave velocity of the top 30 m subsurface, Vs(30), has been used for seismic site classification in accordance with the National Earthquake Hazard Reduction Program (NEHRP) and various building codes. In this study, an attempt has been made to retrieve the geospatial variation of average shear-wave velocity for Coimbatore city using the active Multichannel Analysis of Surface Waves (MASW) test which is one of the non-destructive geophysical tests. To retrieve the spatial distribution of shear-wave velocity (Vs), the test was carried out at 35 locations in the vicinity of important structures, schools, colleges, and hospitals within the city. The seismic records have been acquired in the field and analyzed using the winMASW software. From the one-dimensional MASW test, the study area has an average Vs(30) in the range of 640 m/s to 909 m/s and has been classified as site-class BC (soft rock) according to NEHRP standards. These test results have been validated using the collected SPT bore log data from various locations, including 40 sites in the vicinity of the conducted MASW tests. The site-specific correlation between the shear-wave velocity (Vs) and the corrected SPT N- Value, N1(60), and between Vs and shear modulus (G) have been developed for Coimbatore city with a regression coefficient of 0.79 and 0.83 respectively. From the fundamental site period map, the study area has a site period in the range of 0.1 to 0.2 s, which indicates that 1to 2- storey buildings that are densely distributed throughout the city may lead to damage in case of probable future earthquakes. This study bridges the connectivity from the evaluated bedrock acceleration using the Seismic Hazard Analysis (SHA) and provides insights for evaluating surface acceleration using GRA studies.

The severe damage observed in the Kathmandu Basin, Nepal, during past earthquakes necessitates a thorough study of the seismic behavior of the basin sediments. As the shear-wave velocity is directly related to the elastic shear modulus of the material, it is essential to determine it to incorporate the behavior of the soil in the design of the structure. Hence, we determined average shear-wave velocity in upper 30 m (Vs30) of soil in Bhaktapur district in the eastern part of the Kathmandu Basin at 73 observation points, employing two methods involving the use of non-invasive microtremor array measurements (MAMs). These MAMs are widely used for determining subsurface soil characteristics by analyzing the ambient vibrations of the ground. The first method involves inversion using a genetic algorithm, and the second is a method for obtaining Vs30 directly from the dispersion curve. We found that Vs30 in the southeastern part of the study area was higher than that in other parts. Conversely, Vs30 in the western region was lower. The calculated Vs30 values were used to classify the sites. The elevated eastern and southeastern areas with high Vs30 were categorized as dense soil or soft rock, whereas the areas with low Vs30 that had suffered significant damage during the 2015 Gorkha earthquake were classified as soft soil sites.

It is known that the site classifications are closely related to the damages caused by earthquakes in areas with increased seismic hazard. Additionally, another important parameter utilized to identify the damage is the Peak Ground Acceleration (PGA) value. While measurements and the GMPE are utilized to identify PGA values, site classification is usually conducted by using the Vs30 value. This study aims to identify the site classifications for Bursa province by using a different approach, namely, the H/V spectral ratio method based on the dominant periods. In this regard, 205 records belonging to 82 earthquakes recorded by 41 strong ground motion stations located in Bursa province were utilized. A mean H/V spectral ratio curve was developed for each station based on the Fourier and response spectra of these earthquake records. Generally, double or multiple peaks resulting from the site structure were observed in the H/V curves. Furthermore, for the station locations, the evaluations were conducted in accordance with the site classifications per the dominant period as it is suggested in the literature. The stations were identified as all of the site classifications suggested by (Zhao et al. Bull Seismol Soc Am 96:914-925, 2006), as SC-1, 2, 3 and 5 suggested by (Fukushima et al. J Earthquake Eng 11:712-724, 2007) and as CL I, II, III, IV and VII suggested by (Di Alessandro et al. Bull Seismol Soc Am 102:680-695, 2012). Additionally, various Spectral Acceleration estimations were made with different GMPE equations for scenario earthquakes, and the results were compared with the design spectra suggested by the Turkish Building Earthquake Code (TBEC 2018). As a result of the study, the H/V spectral curves were generated according to both Fourier and response spectra; using a great number of earthquake data, the hazard was assessed by the soil dominant period-based for the first time in Bursa province.