Soil-Structure Resonance Study Using Microtremor Measurements in Srinagar City, Kashmir Valley

Dynamic characterization of soil and structures is important in regions like Kashmir Valley, which lies in the seismically active Himalayan region that has a history of large-magnitude earthquakes. This study aims at finding the possible chances of double resonance in soil and structure and, hence, risk assessment of the site. A four-storied L-shaped building was selected at the National Institute of Technology, Srinagar, for this purpose. In addition to basic soil testing, microtremor horizontal-to-vertical spectral ratio (MHVSR) was used to determine the resonance frequency of both the building and the soil under free-field conditions. Multichannel analysis of surface wave (MASW) was used to estimate the time-averaged shear wave velocity up to 30 m depth (Vs30). For the soil, MASW results indicated Vs30 equal to 354 m/s, classifying the site as class D (stiff) as per NEHRP seismic site classification, and the HVSR curve indicated multiple peaks at frequencies 0.34, 0.9, and 6 Hz. The amplitude spectral density (ASD) plots in both longitudinal and transverse directions were obtained from microtremor recordings on each floor of the building. The plots showed a fundamental frequency in the range of 4.9–5.2 Hz for the building, which is close to the free-field frequency of 6 Hz. SSR was estimated between 15 and 25%, indicating that the building may exhibit a medium risk of soil-structure resonance. This study demonstrates the use of the microtremor method for the preliminary assessment of soil-structure resonance at a site.