Characteristics of Corner Frequency and Spectral Decay Parameter of Earthquakes in Korea

Abstract

Korea is low to moderate seismic regions where earthquake usually occcurs with small magnitude. In based on recorded earthquake in Korea, characteristic of earthquake can be found and applied to making artificial earthquake. Characteristic of earthquake are stress drop as source characteristic, distance between epicenter and station , inelastic attenuation constant as propagation characteristic and site-dependent parameter as site characteristic. Stress drop are related with the corner frequency. Corner frequency is the frequency that main energy of seismic wave is located. And inelastic attenuation constant are related with the spectral decay parameter. Spectral decay parameter is the decreasing ratio of seismic wave. 13 recorded earthquakes were selected above magnitude 4.0 which occurred inland and less than 100km from the seaside from 2001 to 2014. And 27 stations whose soil types were rock were selected. 151 data recorded from 13 earthquake events were analyzed in this paper. Peak ground acceleration was smaller as the distance between each station and same earthquake event was longer. And spectral acceleration based recorded earthquakes in Korea was large in short period range and was small in long period range comparing IBC code in normalized response spectrum. To find the corner frequency, Jo and Park [4]s method was based on Boore and Atkinsons ground motion model and Snoke [3]s method. The zero-frequency level of the far-field displacement amplitude spectrum was founded by algorithm consisting of the integral of the square of the ground velocity and the cumulative displacement squared so the corner frequency was calculated. By linear regression analysis, interaction formula was and the corner frequency was smaller as distance from epicenter was farther. Also, the spectral decay parameter was a slope between exponential frequency and second corner frequency in Fourier amplitude spectrum. In , site-independent value was founded by using Jo and Park [7]s method which was based on Frankel et al. [6]s coda normalization method. The seismogram envelope of S and Coda wave spectrum was calculated and was 0.000159. Site-dependent value at each station was founded by linear regression analysis. Interaction formula was and the spectral decay parameter was larger as distance from epicenter was farther. In precedent research, Noh and Lee [1] suggested and Jo and Park [4, 7] suggested and . was similar value comparing this paper. If characteristic of earthquake in Korea are reflected in making artificial earthquake model, it can predict a big magnitude artificial earthquake properly.