The high-frequency decay parameter Kappa (κ) in the Alborz Region using broadband seismic waveforms

Abstract

The high-frequency decay parameter (κ) is investigated using the three-component broadband seismograms from 306 earthquakes with M_L 3.1–5.6 recorded at nine Iranian National Broadband Seismic Network (BIN) stations in the Alborz region and adjacent areas. The individual κ values are calculated for both the horizontal and vertical components of each record. The estimated mean horizontal and vertical κ values are 0.051 and 0.035 s, respectively, indicating slightly lower attenuation of high-frequency energy on the vertical component than the horizontal one. The dependence of the kappa values on path and source parameters such as distance, magnitude, and focal mechanism are also investigated. A clear increasing trend is observed for κ values with hypocentral distances for horizontal and vertical components. The zero-distance kappa (κ₀) values for the nine BIN stations are evaluated, and a mean value of 0.013 s is estimated, which is close to the values expected for generic rock sites. The obtained κ values show no significant correlation with the earthquake size in the magnitude range of our events. Furthermore, the κ values are found to be fairly similar for all faulting types, with a slight decrease in κ for strike-slip events; hence, the kappa values are deemed as independent of faulting type.