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http://hdl.handle.net/2122/8003
Authors: | Mancilla, F.* Del Pezzo, E.* Stich, D.* Morales, J.* Ibañez, J.* Bianco, F.* |
Title: | Q_{P} and Q_{S} in the upper mantle beneath the Iberian peninsula from recordings of the very deep Granada earthquake of 2 April 11, 2010. | Journal: | Geophysical Research Letters | Series/Report no.: | /39 (2012) | Publisher: | American Geophysical Union | Issue Date: | 2012 | DOI: | 10.1029/2012GL050947 | Keywords: | Seismic attnuation, Subduction | Subject Classification: | 04. Solid Earth::04.06. Seismology::04.06.09. Waves and wave analysis | Abstract: | Granada (Southern Spain) is a place of rare and enigmatic very deep focus earthquakes, the last one on April 11, 2010, with magnitude of 6.3 and depth of 620 km. We use regional broadband recordings to estimate QP and QS in the mantle for frequencies between 0.25 and 8 Hz, computing the spectra of the direct P- and S-waves with their early P- and S coda. We use the spectral decay method, constraining crustal Q to values given in the literature. We obtain robust estimates of QP in 6 frequency bands (0.25, 0.5,1, 2, 4 and 8 Hz) and of QS in 4 bands (0.25, 0.5,1, 2 Hz). QP in the mantle ranges from 13 at 0.25 Hz to 346 at 8 Hz and QS from 59 at 0.25 to 183 at 2 Hz. The frequency dependence is well fitted by Q = Q0f a with a equal to 0.6 for QS and 1.0 for QP, and Q0 equal to 109 for QS and 63 for QP. The QP/QS ratio is less than 1. These are extreme values within the ranges of mantle Q, QP/QS and a values reported in the literature, indicating strong scattering attenuation and absence of melt. We propose that such values, rather than being an exception, may approximate the average upper mantle, with solid olivine composition and small-scale heterogeneity. |
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