Publication Date:
2017-04-04
Description:
A 1D coda method was proposed by Mayeda et al. (2003) in order to
obtain stable seismic source moment-rate spectra using narrowband coda envelope
measurements. That study took advantage of the averaging nature of coda waves
to derive stable amplitude measurements taking into account all propagation,
site, and S-to-coda transfer function effects. Recently, this methodology was
applied to microearthquake data sets from three subregions of northern Italy (i.e.,
western Alps, northern Apennines, and eastern Alps). Because the study regions were
small, ranging between local-to-near-regional distances, the simple 1D path assump-
tions used in the coda method worked very well. The lateral complexity of this region
would suggest, however, that a 2D path correction might provide even better results if
the data sets were combined, especially when paths traverse larger distances and com-
plicated regions. The structural heterogeneity of northern Italy makes the region ideal
to test the extent to which coda variance can be reduced further by using a 2D Q
tomography technique. The approach we use has been developed by Phillips et al.
(2005) and is an extension of previous amplitude ratio techniques to remove source
effects from the inversion. The method requires some assumptions, such as isotropic
source radiation, which is generally true for coda waves. Our results are compared
against direct S-wave inversions for 1/Q and results from both share very similar
attenuation features that coincide with known geologic structures. We compare our
results with those derived from direct waves as well as some recent results from
northern California obtained by Mayeda et al. (2005) that tested the same tomo-
graphic methodology applied in this study to invert for 1/Q. We find that 2D coda
path corrections for this region significantly improve upon the 1D corrections, in
contrast to California where only a marginal improvement was observed. We attribute
this difference to stronger lateral variations in Q for northern Italy relative to
California.
Description:
Published
Description:
1936-1946
Description:
3.1. Fisica dei terremoti
Description:
JCR Journal
Description:
reserved
Keywords:
Attenuation tomography
;
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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