کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
6430761 | 1634833 | 2011 | 7 صفحه PDF | دانلود رایگان |
![عکس صفحه اول مقاله: Radial Qμ structure of the lower mantle from teleseismic body-wave spectra Radial Qμ structure of the lower mantle from teleseismic body-wave spectra](/preview/png/6430761.png)
We have measured 150,000 P and 130,000 S wave spectral ratios up to 0.8 Hz using recordings of 250 deep (focal depth > 200 km) earthquakes from 890 global and regional network stations. We have inverted these data to estimate the attenuation parameters tPâ and tSâ for P and S waves and a radial profile of the quality factor Qμ for the lower mantle. On average, tPâ increases by about 0.2 s and tSâ increases by about 0.7 s between epicentral distances of 30° and 97°. The relatively strong increase of tSâ (ts â 4tPâ) suggests that intrinsic shear attenuation is the cause of the overall trend in our data. The increase of tPâ and tSâ with distance is smaller than predicted by models PREM [12], QL6 [11], and QLM9 [16]. Assuming PREM values for Qμ in the upper mantle, where the data lack resolving power, the P and S wave spectra are explained best if Qμ increases from about 360 at PREM's 670-km discontinuity to 670 in the lowermost mantle. The high values for Qμ can be reconciled with previously determined values by invoking a frequency-dependence of Qμ(Ï) that is proportional to Ï0.1. Data that are separated in 'Pacific' and 'circum-Pacific' subsets have slightly different trends. Estimates of tPâ and tSâ for the Pacific data, which sample the large low shear-velocity province of the Pacific, are higher than the circum-Pacific estimates. Thus, it appears that the Pacific large low shear velocity province has accompanying low Qμ. The difference in Qμ in the lowermost 1000 km of the mantle beneath the Pacific and beneath the circum-Pacific is at most 17%. Lateral variations of this magnitude are marginally resolvable given the uncertainties of our measurements.
Research highlights⺠Lower mantle Qμ profile is estimated from teleseismic body-wave spectra. ⺠tPâ and tSâ increase by about 0.2 s and 0.7 s, respectively, between 30° and 97°. ⺠Qμ increases with depth with a rate of 0.12 km-1. ⺠Reduced Qμ of up to 17% is resolved in the lower mantle beneath the Pacific.
Journal: Earth and Planetary Science Letters - Volume 303, Issues 3â4, 1 March 2011, Pages 369-375