Kappa(<i>κ</i>) from Records of Small Earthquakes in North China

Abstract

At high frequencies, there is an obvious descending of Fourier spectrum amplitude of ground motion acceleration. This fact could be described by a low0pass filter that is controlled by parameter Kappa (κ). In most regions of the world, there are not sufficient strong ground motion records to evaluate this regional parameter. We try to acquire κ value from small-earthquake records of the broadband digital seismograph network in North China (36°-43°N, 113°-120°E). Total 1995 records from 28 small earthquakes (Mw=3.5-4.5) recorded at 155 stations of China Earthquake Network during February of 2002 to September of 2012, are analyzed. The κ value is acquired from the slope rate of the decay segment of the calculated Fourier spectrum of each record, and the mean value is obtained. The result is analyzed if κ is magnitude, focal depth or distance dependent. For the magnitude-dependence, κ values of 40 strong ground motion records are also obtained and compared. The result of the paper shows that κ is not magnitude-dependent neither focal depth-dependent. The distance-dependent is not obvious, especially for small earthquake.