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 s...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.展开更多
We investigate attenuation scattering and loss properties in Souss basin(SW of High-Atlas) as a transition zone between the High and Anti Atlas ranges. This district consists in a thinned crustal patch with shallow se...We investigate attenuation scattering and loss properties in Souss basin(SW of High-Atlas) as a transition zone between the High and Anti Atlas ranges. This district consists in a thinned crustal patch with shallow seismicity and loose sedimentary trenches that perform an important contribution to augment seismic attenuation. So far, no coda waves approach in our knowledge have been used to draw satisfying outputs about the attenuation properties in the region. Therefore, this update suggests to correlate the lateral changes of seismic attenuation to different characteristics and asperities i.e. seismic activity,crustal age and thickness, heat flow, and ground deformation rate. To do so, we analysed coda waves derived from waveform data of more than 23 local earthquakes from seven broadband seismometers recorded during 2010 e2012 period. As a starter, we utilized the backscattering model which defines theseismic attenuation as inversely proportional to quality factor by the equation A ?1=. QQcestimates c were deducted at various central frequency bands 1.5, 3.0, 6.0, 9.0, 12.0 and 18.0 Hz according to different lapses times. The estimated average frequency dependence quality factor gives relation Qc? 120 f1;01,while the average Qcvalues vary from 149 at 1.5 Hz to 1895 at 18 Hz central frequencies. We observed an intimate dependence between quality factor and frequency ranges, which reflects the complexity of geological/geophysical pattern in the Souss basin and the presence of a variety of heterogeneities within the underlying crust.展开更多
For short-period near-earthquake records in eastern China,from the empirical attenuation formula of coda ground motion amplitude A with timeτ:lgA=G-2.235lgτ,using the single scattering theory modified with epicentra...For short-period near-earthquake records in eastern China,from the empirical attenuation formula of coda ground motion amplitude A with timeτ:lgA=G-2.235lgτ,using the single scattering theory modified with epicentral distance,we obtain the curve family of corrected coda amplitude Ac(r,t),and w/2Qc values for each time interval of coda. From this,Qc(f,h) values, which correspond to each observational average frequency and sampling depth,are calculated.The results substantially agree with those observational Qc values in Yunnan,Beijing and central Asia.展开更多
Based on the single scattering model of seismic coda waves, we have calculated the Q-factor in Beijing and its surrounding regions by means of calculating the power density spectrum in frequency domain with a fixed ti...Based on the single scattering model of seismic coda waves, we have calculated the Q-factor in Beijing and its surrounding regions by means of calculating the power density spectrum in frequency domain with a fixed time window. The digital seismic data of 69 earthquakes from Beijing Telemetered Seismographic Network are used.These earthquakes were recorded from January 1, 1989 to December 31,1990 at 20 stations. This paper shows the variations of the coda Q-factors in the studied region with different sites, frequency and lapse time, and the temporal change of the coda Q-factors in these two years. The results indicate that coda Q-factor depends strongly on the lapse time and frequency. It is assumed that when Qc=Q0f″, for the three time windows of 15 -30 s, 30-60 s and 60-90 s, the average values of Q0 are 48, 115 and 217; and the average values of ηare 0.89, 0. 91 and 0. 74, respectively.展开更多
基金sponsored by the Natural Science Foundation of Shandong Province (Y2007E09)Joint Earthquake Science Foundation (C08028)Special Application Research of Digital Seismic Wave Data ,Shangdong,China
文摘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.
基金supported by the Scientific Institute, Rabat, Morocco
文摘We investigate attenuation scattering and loss properties in Souss basin(SW of High-Atlas) as a transition zone between the High and Anti Atlas ranges. This district consists in a thinned crustal patch with shallow seismicity and loose sedimentary trenches that perform an important contribution to augment seismic attenuation. So far, no coda waves approach in our knowledge have been used to draw satisfying outputs about the attenuation properties in the region. Therefore, this update suggests to correlate the lateral changes of seismic attenuation to different characteristics and asperities i.e. seismic activity,crustal age and thickness, heat flow, and ground deformation rate. To do so, we analysed coda waves derived from waveform data of more than 23 local earthquakes from seven broadband seismometers recorded during 2010 e2012 period. As a starter, we utilized the backscattering model which defines theseismic attenuation as inversely proportional to quality factor by the equation A ?1=. QQcestimates c were deducted at various central frequency bands 1.5, 3.0, 6.0, 9.0, 12.0 and 18.0 Hz according to different lapses times. The estimated average frequency dependence quality factor gives relation Qc? 120 f1;01,while the average Qcvalues vary from 149 at 1.5 Hz to 1895 at 18 Hz central frequencies. We observed an intimate dependence between quality factor and frequency ranges, which reflects the complexity of geological/geophysical pattern in the Souss basin and the presence of a variety of heterogeneities within the underlying crust.
文摘For short-period near-earthquake records in eastern China,from the empirical attenuation formula of coda ground motion amplitude A with timeτ:lgA=G-2.235lgτ,using the single scattering theory modified with epicentral distance,we obtain the curve family of corrected coda amplitude Ac(r,t),and w/2Qc values for each time interval of coda. From this,Qc(f,h) values, which correspond to each observational average frequency and sampling depth,are calculated.The results substantially agree with those observational Qc values in Yunnan,Beijing and central Asia.
文摘Based on the single scattering model of seismic coda waves, we have calculated the Q-factor in Beijing and its surrounding regions by means of calculating the power density spectrum in frequency domain with a fixed time window. The digital seismic data of 69 earthquakes from Beijing Telemetered Seismographic Network are used.These earthquakes were recorded from January 1, 1989 to December 31,1990 at 20 stations. This paper shows the variations of the coda Q-factors in the studied region with different sites, frequency and lapse time, and the temporal change of the coda Q-factors in these two years. The results indicate that coda Q-factor depends strongly on the lapse time and frequency. It is assumed that when Qc=Q0f″, for the three time windows of 15 -30 s, 30-60 s and 60-90 s, the average values of Q0 are 48, 115 and 217; and the average values of ηare 0.89, 0. 91 and 0. 74, respectively.
文摘地表疏松介质对地震波高频成分的吸收、衰减是造成沙漠地区资料分辨率降低的关键原因.通过野外实际测量和实验室测定,在新疆塔里木盆地和准噶尔盆地表层沙的品质因子与地震纵波具有良好函数关系.应用层析速度反演计算出表层沙的纵波速度,进而得到其品质因子分布,利用反Q滤波对地震资料进行吸收补偿.结果表明,该方法可以有效提高地震资料的分辨率,有效频带和主频均可提高10 Hz.
