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A local magnitude scale for crustal earthquakes in Italy
Language
English
Obiettivo Specifico
2T. Tettonica attiva
Status
Published
JCR Journal
JCR Journal
Peer review journal
Yes
Title of the book
Issue/vol(year)
1/106(2016)
ISSN
0037-1106
Electronic ISSN
1943-3573
Publisher
Seismological Society of America
Pages (printed)
242-258
Issued date
February 2016
Abstract
In this study a new local magnitude (ML) scale is derived for the Italian region from the
analysis of seismic signals recorded by a dense broad-band network between 2003
and 2009. The ML computation is performed by measuring peak amplitudes of
synthetic Wood-Anderson seismograms. Based on Richter's original definition, these
amplitudes are inverted for earthquake magnitudes, site-corrections and the distance dependent
term that corrects amplitudes for geometrical spreading and scattering-anelastic
attenuation. The latter is expressed as function of R (hypocentral distance)
and log R by means of a two-parameter linear form, and constrained at the distance of
100 km in accordance with Richter's definition. Using the newly derived distance dependent
term and site-corrections, magnitudes are consistently estimated for the
stations recording each earthquake, within an overall root mean square (RMS) residual
of 0.18. No anomalous trend with distance is appreciable in the magnitude residuals,
for the Italian region as a whole and smaller areas along the Italian peninsula as well.
The only exception is represented by northeastern Italy where increasingly negative
residuals are observed for distances decreasing below 100 km. Spatial pattern of site corrections
reveals contrasting attenuation properties of the crust
between the Tyrrhenian side of the Italian peninsula (west of the Apennines, high
attenuation) and the Adriatic side (east of the Apennines, low attenuation), as
previously found in other studies. Finally, the magnitudes computed with the new ML
scale are compared with global estimates of body-wave magnitude (mb) and local and
regional estimates of moment magnitude (Mw), finding a satisfactory agreement in
most of the magnitude range considered (roughly from 3 to 5.5).
analysis of seismic signals recorded by a dense broad-band network between 2003
and 2009. The ML computation is performed by measuring peak amplitudes of
synthetic Wood-Anderson seismograms. Based on Richter's original definition, these
amplitudes are inverted for earthquake magnitudes, site-corrections and the distance dependent
term that corrects amplitudes for geometrical spreading and scattering-anelastic
attenuation. The latter is expressed as function of R (hypocentral distance)
and log R by means of a two-parameter linear form, and constrained at the distance of
100 km in accordance with Richter's definition. Using the newly derived distance dependent
term and site-corrections, magnitudes are consistently estimated for the
stations recording each earthquake, within an overall root mean square (RMS) residual
of 0.18. No anomalous trend with distance is appreciable in the magnitude residuals,
for the Italian region as a whole and smaller areas along the Italian peninsula as well.
The only exception is represented by northeastern Italy where increasingly negative
residuals are observed for distances decreasing below 100 km. Spatial pattern of site corrections
reveals contrasting attenuation properties of the crust
between the Tyrrhenian side of the Italian peninsula (west of the Apennines, high
attenuation) and the Adriatic side (east of the Apennines, low attenuation), as
previously found in other studies. Finally, the magnitudes computed with the new ML
scale are compared with global estimates of body-wave magnitude (mb) and local and
regional estimates of moment magnitude (Mw), finding a satisfactory agreement in
most of the magnitude range considered (roughly from 3 to 5.5).
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article
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