Publication Date:
2021-09-03
Description:
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.
Description:
Published
Description:
L09303
Description:
3.1. Fisica dei terremoti
Description:
JCR Journal
Description:
restricted
Keywords:
Seismic attnuation, Subduction
;
04. Solid Earth::04.06. Seismology::04.06.09. Waves and wave analysis
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
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