THE Q-FACTORS AS A FUNCTION OF FREQUENCY IN THE TANGSHAN-BEIJING AREA

Making use of the records of the Frequency Selective Seismographs in the Tangshan-Beijing area, the apparent Q-factor around every station has been obtained by means of the single station method. To form the combined envelops of codas from several records at the same station this paper proposed the relation △lnA= 1.73△M, where △Mis the difference between the measured magnitude and the normalized reference magnitude as a relatively rigid criterion of compensation to substitute the method of estimate by the eye. Thus more reasonable combined envelops of codas have been constructed, which provide the apparent Q-factors as the statistical representation for a certain area around the station. The variation of Q-factor versus frequency has also been reconfirmed as Q-Qof, where Qo is the Q-factor at 1 Hz, f is the frequency, is a constant which is related to a certain area. It can be noticed that even though there is quite a remarkable difference in Qo among stations in this area under study, for instance, Qo min=122 at Shacheng and Qomax=292 at Madaoyu, the s are almost the same, around 0.6, for five out of the six stations, with Taishitun as the only exception. This shows that the physical substance of the attenuation around these stations can be taken as quite similar. As a statistical result for the whole Tangshan-Bijing area, the overall average of Q-factor at 1 Hz is Q0=189.It is consequently noticeable that in reporting any Q-factor in the range of 1-40 Hz, one has to consider the fact that the Q-factor is strongly dependent on frequency.