Publication Date:
2021-05-12
Description:
An analysis of coda waves excited in the 0.2–20 Hz frequency band and recorded by the underground
array Underseis (central Italy) has been performed to constrain both seismic attenuation at regional scale
and velocity structure in the Mount Gran Sasso area. Attenuation was estimated with the MLTWA
method, and shows a predominance of scattering phenomena over intrinsic absorption. The values of
Qi and Qs are compatible with other estimates obtained in similar tectonic environments. Array methods
allowed for a detailed study of the propagation characteristics, demonstrating that earthquake coda at
frequencies greater than about 6 Hz is composed of only body waves. Coherence and spectral characteristics
of seismic waves measured along the coda of local and regional earthquakes indicate that the wavefield
becomes fully diffuse only in the late coda. The frequency-dependent energy partitioning between
horizontal and vertical components has been also estimated and compared with synthetic values
computed in a layered half-space under the diffuse field assumption. This comparison confirms that,
for frequencies higher than 6 Hz, the coda appears as a sum of body waves coming from all directions
while, in the low frequency range (0.2–2 Hz), the observations can be well explained by a coda wavefield
composed of an equipartition mixture of surface and body waves traveling in a multiple-layered medium.
A Monte-Carlo inversion has been performed to obtain a set of acceptable velocity models of the upper
crust. The present results show that a broadband coda wavefield recorded in an underground environment
is useful to constrain both the regional attenuation and the velocity structure of the target area,
thereby complementing the results of classical array analysis of the wavefield.
Description:
Published
Description:
34 - 42
Description:
4T. Fisica dei terremoti e scenari cosismici
Description:
JCR Journal
Description:
restricted
Keywords:
Energy equipartition
;
Scattering
;
velocity/attenuation structure
;
array analysis
;
Diffuse wavefield
;
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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