| Many scholars have been studying the mechanism and attenuation characteristics of S-wave coda of local earthquake, since the single back scattering model was proposed firstly by Aki K.in 1969. Seismologists use coda QC for the description of wave code attenuation. Coda QC called as crustal medium quality factor, is an important physical quantity which is used for the study on the characteristics of crustal medium and seismic activity. Coda QC is attemptted to be used in earthquake prediction by the study on its temporal-spatial characteristics. Midwestern Inner Mongolia monitored by CEA and Earthquake Administration of Inner Mongolia Autonomous Region for years, is the complicated geological structure, intense neotectonic movement, and seismically active area. In this paper, the characteristics of coda QC in Midwestern Inner Mongolia (38.5o～42.5oN; 105o～115oE) are studied based on the single scatter model (Aki).1. In order to study the influence on QC values by different frequencies, three seismic waveforms are processed. The results show that QC values at different frequencies are different significantly, and increase with frequencies.2. Ten seismic waveforms are processed, and most results show that the QC values have the fluctuation change with the lengths when the lengths of coda windows are during 30～50 seconds, what may be related to the unstable data resulted from small lengths of coda windows. And the QC values increase with the lengths when the lengths of coda windows are during 52.5～80 seconds. Stress increases with depth, and the heterogeneity of medium decrease, the sampling depth of the part arrived firstly is bigger than the one of the part arrived secondly, so QC values increase with the lengths of coda window.3. QC values in the coda window of 2tS～60 seconds and in the one of 2tS～70 seconds in the periphery areas of ten seismic stations in Midwestern Inner Mongolia are both calculated. The results in different coda windows both show that there exists negative relationship between Q0 value andηvalue. The Q0 values in different coda windows in the periphery areas of the same seismic station are different, but the characteristics of their spatial distribution are same.4. There exists good consistency between the regional difference of the coda QC and the one of tectonic activity, seismically activity, crustal velocity structure and heat flow. QC values in complicated geological structure, intense neotectonic movement, seismically active, low speed and high heat flow areas are low, what means that seismic waves attenuate rapidly.5. The temporal changes of QC values in the periphery areas of Xishanzui and Wuhai seismic station are analyzed. In the periphery areas of Xishanzui seismic station, average QC value at 1HZ from 2005 to 2008 is 10.56% lower than the one from 2001 to 2004,but average QC values at 8HZ, 14 HZ and 18 HZ from 2005 to 2008 are higher than the ones from 2001 to 2004 with the value of 4.47%, 0.86%, 2.45% respectively. In the periphery areas of Wuhai seismic station, average QC value at 14HZ from 2005 to 2008 is 2.89% lower than the one from 2001 to 2004,but average QC values at 1HZ, 8 HZ and 18 HZ from 2005 to 2008 are higher than the ones from 2001 to 2004 with the value of 9.43%, 2.25%, 7.35% respectively. 6. In Midwestern Inner Mongolia, the relation between QC and f is QC(f)=(168.1±64.30)f(0.8498±0. 1771)in the coda window of 2tS～60 seconds, and is QC(f)=(273.3±73.15)f(07521±0.1784)in the coda window of 2tS～70 seconds. Q0 values in Midwestern Inner Mongolia are higher than the ones in Chendu Telemetric Seismic Network region and Xichang where tectonic activities and seismic activities are high, and the ones in Zhangbei earthquake area, lower than the ones in the northern sea area and the inland area of eastern Shandong where tectonic activities and seismic activities are low.7. The comparison study of the results based on the single scatter model (Aki) and based on the single scatter model (Sato), shows that QC values obtained by various methods are different, but the characteristics of their spatial distribution are same, what proved that the results obtained by two methods are both credible, and it has no influence on the characteristics of their spatial distribution to use various methods.
|
PDF Full Text Request