Bihar, an Indian state located in seismic zones III, IV, and V, has experienced severe earthquakes in the past. Due to the presence of alluvium soil deposits over the bedrock in the Bihar region, seismic waves near the ground surface can amplify and cause catastrophic damage to existing structures. Therefore, to ensure the safety of the structures, it is imperative to assess the amplification level of seismic waves near the surface. This study presents a new empirical correlation for the site classes C, D, and E of the Bihar region, which estimates the spectral acceleration (Sa) at the required time period. These site classes of the Bihar region refer to the classification of soil and geological conditions based on their behaviour during seismic events, specifically their impact on seismic wave amplification, ground shaking, and overall earthquake hazard, as per NEHRP classification. The results of this investigation can be applied to enhance the seismic design of structures and, hence, mitigate the seismic risk. Moreover, the developed empirical correlation for Sa can be used to estimate the design spectrum acceleration at the surface level for site classes C, D, and E of the Bihar region.

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.

Maharashtra stands out as a crucial state in India, demonstrating significant progress in infrastructural development and industrialization. Several prominent cities, including Mumbai, Pune, Nagpur, etc., are significantly contributing to the Indian economy. Considering the importance of the state, a deterministic seismic hazard analysis is executed to reduce the damages to critical and important structures and fatalities caused due to earthquakes. Past earthquakes data are collected within and around the state to prepare a homogenised earthquake catalogue. Seven seismic zones are prepared using K- mean cluster analysis. Independent earthquake events i.e., mainshocks are identified using four renowned declustering methods. Additionally, with the help of mainshocks from each zone, the maximum observed earthquake magnitude ( m(max)) and positive correction factor (Delta) are estimated. By superimposing all the m (max) mainshocks (after adding A) onto the fault map, the maximum observed possible earthquake magnitude of all faults (M-max) are assigned to each fault. M-max value is used to estimate surface rupture length (RLD) and consecutively, the maximum magnitude (M-Max) from fault sources are estimated. Three region-specific ground motion prediction equations (GMPEs) are adopted in the logic trees assigning a proper weightage to each GMPE. A seismic hazard contour maps are prepared at bedrock level, C, and D-type soil sites for Maharashtra. In the western part of the study area, the maximum PGA value is found to be 0.58 g, 0.70 g, and 0.33 g at bedrock level, C, and D-type sites, respectively.