Variation of Q value before and after the 1999 Xiuyan, Liaoning Province, M=5.4 earthquake on the basis of analysis on attenuation dispersion of P waves

Introduction The medium in the Earth is inhomogeneous, anelastic and anisotropic. By studying the at- tenuation of seismic waves we can acquire some information on the component and property of the material, as well as temperature distribution in the Earth. Dispersion of body waves is caused by the anelasticity of the medium (Wuenschel, 1965; Doornbos , 1983). There are two kinds of approach for studying the wave attenuation: amplitude decay and dispersion. Based on wave am- plitude decay me…

Variation of Q value before and after the 1999 Xiuyan, Liaoning Province, M=5.4 earthquake on the basis of analysis on attenuation dispersion of P waves

A method for determining medium quality factor is developed on the basis of analyzing the attenuation dispersion of the arrived first period P wave. In order to enhance signal to noise ratio, improve the resolution in measurement and reduce systematic error we applied the data resampling technique. The group velocity delay of P wave was derived by using an improved multi-filtering method. Based on a linear viscoelastic relaxation model we deduced the medium quality factor Qm, and associated error with 95% confidence level. Applying the method to the seismic record of the Xiuyan M=5.4 earthquake sequences we obtained the following result: 1 High Qm started to appear from Nov. 9, 1999. The events giving the deduced high Qm value clustered in a region with their epicenter dis- tances being between 32 and 46 km to the Yingkou station. This Qm versus distance observation obviously deviates from the normal trend of Qm linearly increasing with distance. 2 The average Qm before the 29 Dec. 1999 M=5.4 earthquake is 460, while the average Qm between the M=5.4 event and the 12 Jan. 2000 M=5.1 earthquake is 391, and the average Qm after the M=5.1 event is 204.