Publication Date:
2017-04-04
Description:
Following the numerical scheme of Yoshimoto we synthesized seismogram envelopes in the
multiple scattering framework.We supposed the earth model constituted by a inhomogeneous
crust overlying a transparent mantle. In this model velocity is assumed depth-dependent
through a continuous function of the depth, v = v(h); Moho discontinuity is approximated by
a sharp increase of the velocity around the crust–mantle boundary; inhomogeneity in the crust
is parametrized through a depth-dependent scattering coefficient (the inverse of mean free
path) g = g0 f (h), with f (h) function of depth, and g0 the scattering coefficient at zero depth;
intrinsic attenuation is parametrized in terms of the intrinsic attenuation coefficient, ηi , that is
assumed independent of depth. Generating a suite of energy envelopes as a function of lapse
time and distance, for reasonable values of B0 , the seismic albedo and Le−1, the extinction
length inverse (which are functions of g0 and ηi ), we span a wide range including most of
the measurements done through the world. Then, we apply the ordinary MLTWA technique to
these synthetic envelopes. In this application, we assume a constant g and a constant velocity,
v = 〈v(h)〉 which equals the average of v(h) calculated in the depth range characteristic
of the volume encompassed by the scattered waves. In this way, we obtain the estimates of
B0, and Le−1, for a constant half-space. The relationship between the estimates of B0 and
Le−1, obtained assuming half-space, and the correspondent values used in the simulation,
results to be well approximated by a second-order polynomial. Then, evaluating the best fit
polynomial coefficients, we obtain a correspondence map between attenuation parameters
retrieved for a uniform model with those characteristic of a more realistic structure. This map
is useful to reinterpret all the couples B0 and Le−1 already calculated through the world in
geological structures similar to the one adopted in our simulation. Results show that scattering
and intrinsic-attenuation coefficients estimated using MLTWA in the assumption of a uniform
half-space are always overestimated
Description:
Published
Description:
949-955
Description:
3.1. Fisica dei terremoti
Description:
JCR Journal
Description:
reserved
Keywords:
Coda waves
;
Seismic attenuation
;
Wave scattering and diffraction
;
04. Solid Earth::04.06. Seismology::04.06.99. General or miscellaneous
;
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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