Publication Date:
2017-04-04
Description:
In the Umbria Marche (Central Italy) region an important earthquake sequence occurred in 1997,
characterized by nine earthquakes with magnitudes in the range between 5 and 6, that caused
important damages and causalities. In the present paper we separately estimate intrinsic- and
scattering- Q
−1
parameters, using the classical MLTWA approach in the assumption of a half space
model. The results clearly show that the attenuation parameters Qi
−1
and Qs
−1
are frequency
dependent. This estimate is compared with other attenuation studies carried out in the same area, and
with all the other MLTWA estimates obtained till now in other tectonic environments in the Earth.
The bias introduced by the half space assumption is investigated through numerical solutions of the
Energy Transport equation in the more realistic assumption of a heterogeneous crust overlying a
transparent mantle, with a Moho located at a depth ranging between 35 and 45 km below the surface.
The bias introduced by the half space assumption is significant only at high frequency. We finally
show how the attenuation estimates, calculated with different techniques, lead to different PGA decay
with distance relationships, using the well known and well proven Boore’s method. This last result
indicates that care must be used in selecting the correct estimate of the attenuation parameters for
seismic risk purposes. We also discuss the reason why MLTWA may be chosen among all the other
available techniques, due to its intrinsic stability, to obtain the right attenuation parameters.
Description:
Published
Description:
1370-1382
Description:
4T. Fisica dei terremoti e scenari cosismici
Description:
JCR Journal
Description:
open
Keywords:
Seismic attenuation
;
scattering
;
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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