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Source-Parameter Estimation after Attenuation Correction through the Use of Q Tomography
Author(s)
Language
English
Obiettivo Specifico
OST3 Vicino alla faglia
Status
Published
JCR Journal
JCR Journal
Peer review journal
Yes
Title of the book
Issue/vol(year)
4/113 (2023)
ISSN
0037-1106
Publisher
Seismological Society of America
Pages (printed)
1739–1758
Issued date
2023
Abstract
The measurement of earthquake source parameters is affected by large uncertainties, and
different approaches lead to large variability in results. One crucial aspect is the trade-off
between attenuation (Q) and corner frequency (fc ) in spectral fitting: The source corner
frequency, inversely proportional to the fault size, can be severely masked by attenuation
and site effects. In this article, we describe a method to solve the trade-off based on the fit
of displacement spectra to find the source characteristics (corner frequency, f c , and the
signal moment, Ω0) and the single-station attenuation operator (t ), in addition to the site
response. We follow a parametric approach based on the use of 3D Q seismic tomography
and a bootstrap-based method for selecting the best spectra fit. The correction of attenu-
ation with synthetic values derived by 3D attenuation tomography efficiently deals with
the trade-off between source and path terms, leading to small uncertainties in the deter-
mination of source unknowns (f c and signal moment, Ω0 ), thus yielding constrained esti-
mates of source parameters for low- to medium-magnitude earthquakes. We show an
application to the Emilia 2012 seismic sequence, for which we computed the source param-
eters for 1240 aftershocks (from an initial dataset of 1748) with local magnitude ranging
from 2.0 to 4.7 using the spectral fit from P and S waves. About 80% of stress-drop esti-
mations are characterized by relatively low uncertainties (within 20% of the estimated
values), with maximum values of about 40% for the remaining 20%. The attenuation cor-
rection is effective to determine source parameters for small-magnitude earthquakes;
hence, we obtain reliable estimates of source parameters for the entire aftershock
sequence. This approach gives the opportunity to infer the mechanical state of a complete
fault system by taking advantage of the larger number of low-magnitude events (with
respect to the largest ones) that always follow a major earthquake.
different approaches lead to large variability in results. One crucial aspect is the trade-off
between attenuation (Q) and corner frequency (fc ) in spectral fitting: The source corner
frequency, inversely proportional to the fault size, can be severely masked by attenuation
and site effects. In this article, we describe a method to solve the trade-off based on the fit
of displacement spectra to find the source characteristics (corner frequency, f c , and the
signal moment, Ω0) and the single-station attenuation operator (t ), in addition to the site
response. We follow a parametric approach based on the use of 3D Q seismic tomography
and a bootstrap-based method for selecting the best spectra fit. The correction of attenu-
ation with synthetic values derived by 3D attenuation tomography efficiently deals with
the trade-off between source and path terms, leading to small uncertainties in the deter-
mination of source unknowns (f c and signal moment, Ω0 ), thus yielding constrained esti-
mates of source parameters for low- to medium-magnitude earthquakes. We show an
application to the Emilia 2012 seismic sequence, for which we computed the source param-
eters for 1240 aftershocks (from an initial dataset of 1748) with local magnitude ranging
from 2.0 to 4.7 using the spectral fit from P and S waves. About 80% of stress-drop esti-
mations are characterized by relatively low uncertainties (within 20% of the estimated
values), with maximum values of about 40% for the remaining 20%. The attenuation cor-
rection is effective to determine source parameters for small-magnitude earthquakes;
hence, we obtain reliable estimates of source parameters for the entire aftershock
sequence. This approach gives the opportunity to infer the mechanical state of a complete
fault system by taking advantage of the larger number of low-magnitude events (with
respect to the largest ones) that always follow a major earthquake.
Type
article