We used 16 aftershock recordings of the 2015 Gorkha earthquake (Mw 7.8) at three temporary stations inside the Kathmandu Valley to derive earthquake H/V spectral ratios (EHVSRs) and compare those with microtremor H/V spectral ratios (MHVSRs) at same stations. The predominant frequency peaks of EHVSRs and MHVSRs are comparable at three continuous observation stations with three-component accelerometers; NAKRM (0.6 Hz), NANST (0.32 Hz) and NABKT (2.2 Hz) suggesting that accelerometers can sometimes be used to investigate response of the deep sedimentary basin. We also derived MHVSRs using microtremor data at 11 temporary sites inside the Kathmandu Valley to obtain dominant frequencies. Next we estimated the thickness of sedimentary layer by calculating theoretical H/V ratio with simplified four-layered velocity model and compared them with the derived MHVSRs. The estimations indicate that the thickness of sedimentary layer ranges from 42 to 700 m. We also investigated amplification and attenuation property of S-waves inside Kathmandu using three earthquakes; one teleseismic event and two aftershocks of the 2015 Gorkha earthquake. Observed data clearly showed that the basin amplifies ground motion in the low frequency range (0.1 – 1.0 Hz), while high-frequency ground motion (>1 Hz) do not rapidly decay in the Kathmandu Valley.
Keywords: H/V spectral ratio, Site Amplification, Kathmandu Valley, Microtremor, Gorkha Earthquake aftershocks.