Identification of Ground Response Parameters of Itanagar City, Arunachal Pradesh, India, Using Varying Seismic Intensities and Equivalent Linear Analysis Approach

This study assesses the ground response for several typical sites in the Itanagar Region of Arunachal Pradesh, India. The sites were chosen based on their geological characteristics and the seismic history of the region. The region is seismically active and that strong ground motions can be expected in the event of a larger earthquake. In absence of any previous report, the conduct of ground response analysis (GRA) is imperative for this region. This paper reports the GRA of Itanagar region being conducted for the first time in this area. For the exercise, seven borehole locations of the region were selected. Due to the significant effect of strong ground motions on ground response, five different recorded ground motions with peak bedrock acceleration (PBRA) of 0.12 g, 0.22 g, 0.36, 0.43 g and 0.82 g are used. In terms of surface acceleration histories, amplification, shear strain and shear stress ratio variations as well as the response spectrum, it is observed that seismic GRA of Itanagar region is significantly affected by the input motion characteristics and soil variability. Given the subsurface characteristics in the area, the significant surface accelerations with high amplifications are noted. Based on the equivalent linear analysis, peak ground acceleration (PGA) in the range of 0.218–1.853 g is observed based on the various input motions, which corresponded to the amplification factors (i.e. ratio of peak ground acceleration to peak bedrock acceleration) in the range of 1.051–4.356. Depending upon the soil material present at depths below the ground surface, the GRA results also revealed the deamplification of the propagating seismic waves at certain locations. For all five input motions, the maximum spectral acceleration ranges from 0.725 to 9.153 g in the seven locations. The responses from the ground response analysis conducted for the first time in Itanagar region successfully portray the distribution of PGA, amplification factor and spectral acceleration in the region that would massively help in informed design of structures with the inclusion of these a-priori information.