Publication Date:
2017-04-04
Description:
The attenuation of shear waves propagating in the crust of northwestern
Turkey has been investigated in the frequency range 1–10 Hz. A standard spectral
inversion scheme is applied to a data set of 245 aftershocks (ML 4.5) of the 1999
Izmit earthquake. The obtained attenuation-with-distance curves have been described
in terms of the t* cumulative attenuation parameter and its dependence on frequency
and distance investigated. At 1 Hz, Q 1, evaluated by normalizing t* to the travel
time, is generally larger than 0.025 for source-to-station distances smaller than 40 km,
indicating the presence of a highly attenuating upper crust in the area. Over longer
distances, Q 1 decreases, suggesting a decrease in the attenuation with depth. By
contrast, the normalized t* computed for earthquakes recorded at stations having
almost the same distance from the sources do not show a strong dependence on the
backazimuth. These results suggest that the decrease of Q 1 with depth is more
significant than its lateral variations. Regarding its frequency dependence, Q 1 almost
linearly decreases with frequency.
Finally, the near-surface-attenuation parameter k is evaluated at 12 stations and
the results discussed in terms of site, event, and propagation contributions. The event
contribution is not negligible and shows a significant positive correlation with magnitude.
The site term is smaller than 0.020 sec for rock or topographic sites, while it
assumes values of 0.036 sec and 0.042 sec for two stations installed over thick soft
sedimentary layers.
Description:
Published
Description:
188-199
Description:
JCR Journal
Description:
reserved
Keywords:
waves propagating
;
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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