Estimation of Kappa Factor for Nepal Himalaya Using Local Earthquake Data

Abstract

The empirical factor Kappa (k) governs the rapid decay of spectral amplitude at high frequencies. It is one of the crucial parameters required in the simulations of earthquake-strong ground motions. Nepal is one of the most seismically active regions prone to earthquakes because it is at the junction of the Indian and Eurasian tectonic plates. In our present study, kappa factor is estimated for the Eastern Nepal using local earthquake data collected through the deployment of six-station network around the ARUN-3 Hydro Electric Project , a venture of Government of India. Digital seismographs consisted of Triaxial seismometer (20 sec compact Trillium) at four stations namely, PHAK, KUTI, MAHI and KHAN stations) and Broad-Band Triaxial Seismometer (120 sec Trillium) at two stations namely, ADIT, BHOJ coupled with digital recorder (Centaur) have been deployed for recording of microearthquakes at six stations. The estimated values of k vary from 0.01-0.04 with an average kappa value of 0.028. Our results show no significant dependence of κ on epicentral distance for the region and local site conditions play a major role in the estimation of k. One of the important observations of this study is that κ is not the source property for Nepal Himalayan region. The estimated values of the κ are useful for the stochastic simulation of earthquake strong ground motions.