The Quality factor is the parameter that can be used to describe the energy attenuation on seismic wave. In theory, we can obtain the relationship between the change of the coda wave quality factor with time and the strong earthquake preparation process on the basis of the quality factor of a coda wave in a same ray path. However, in reality the coda wave quality factor measured by different seismic coda waves corresponds to different seismic wave ray paths. The change of the quality factor with time is related to non-elastic characteristics of the medium and the volume of scattering ellipsoid constrained by scattered wave phase fronts, besides the change of regional stress field. This paper discusses the relationship between quality factor, epicenter distance and different lapse time, and then discusses the relationship between quality factor and frequency. Furthermore the determination method of the coda wave quality factor is put forward. The improved determination method of the quality factor, which removes the influence of different earthquakes or propagation depth of scattered waves, may increase measurement precision, thus information pertaining to abnormal changes in quality factor and the relationship between the quality factor and earthquake preparation process can be acquired.
Liu Xiqiang Shi Yuyan Qu Junhao Li Hong Li Bo Zhang Kun
On the condition that the velocity ratio of compressive wave to shear wave is stable during the propagating process of seismic wave,this paper develops an estimation method for medium quality factor based on single station's travel time difference between direct S and P waves and the first period signal of direct P wave.8 774 high SNR wave data altogether recorded by 75 stations are analyzed.The results show that:(1)under the normal regional stress field,the quality factors QmSP in the stable tectonic area are higher than that in the active tectonic area around the Weifang-Jiashan section and its surrounding area in the Tanlu fault zone;(2)in the Juxian-Tancheng section the seismic wave attenuation is relatively quick,and the media is relatively broken,suggesting no tectonic stress accumulation;(3)the Xinyi-Sihong section is currently locking and in accumulating elastic strain energy stage,which has the deep environment and conditions of strong earthquake generation similar to those of the 1668 M 8.5 Tancheng strong earthquake.
