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The Location and Sizing of Historical Earthquakes Using the Attenuation of Macroseismic Intensity with Distance
Language
English
Obiettivo Specifico
3.2. Tettonica attiva
Status
Published
JCR Journal
JCR Journal
Peer review journal
Yes
Title of the book
Issue/vol(year)
5A/100 (2010)
Pages (printed)
2035–2066
Issued date
October 2010
Abstract
We herein describe new methods for computing the quantitative parameters
of earthquakes using macroseismic data and the uncertainties associated with
these parameters. The methods allow for the location of epicenters that are offshore
or that have no intensities assigned to any points in the epicentral region by maximizing
the likelihood function of an attenuation equation with observed intensity data. In
the most favorable cases, such an approach also allows the estimation of the source
depth and the local attenuation coefficients. We compute the parameter uncertainties
in two ways: (1) using formal methods, such as the inversion of the Hessian of the loglikelihood
function at its maximum, and (2) by using bootstrap simulations.We tested
the performance of our methods by comparison with reliable instrumental hypocenters
of onshore earthquakes, and found a reasonable agreement with the epicentral locations
(within 10–15 km for more than 70% of cases) but not with the hypocentral
depths, for which our results are generally underestimated by a factor of 2 or more
and are poorly related to instrumental estimates. This finding indicates that the use of
macroseismic depths in seismic hazard and seismotectonic investigations should be
treated with caution. We nevertheless found good agreement (within 10°–15°)
between the fault-trace orientations that were computed using the macroseismic data
and the associated focal mechanisms of earthquakes with Mw ≥5:7. The surprising
accuracy of the macroseismic orientations obtained using this method could in some
cases allow the true fault to be inferred between the two conjugate planes of a given
focal mechanism.
of earthquakes using macroseismic data and the uncertainties associated with
these parameters. The methods allow for the location of epicenters that are offshore
or that have no intensities assigned to any points in the epicentral region by maximizing
the likelihood function of an attenuation equation with observed intensity data. In
the most favorable cases, such an approach also allows the estimation of the source
depth and the local attenuation coefficients. We compute the parameter uncertainties
in two ways: (1) using formal methods, such as the inversion of the Hessian of the loglikelihood
function at its maximum, and (2) by using bootstrap simulations.We tested
the performance of our methods by comparison with reliable instrumental hypocenters
of onshore earthquakes, and found a reasonable agreement with the epicentral locations
(within 10–15 km for more than 70% of cases) but not with the hypocentral
depths, for which our results are generally underestimated by a factor of 2 or more
and are poorly related to instrumental estimates. This finding indicates that the use of
macroseismic depths in seismic hazard and seismotectonic investigations should be
treated with caution. We nevertheless found good agreement (within 10°–15°)
between the fault-trace orientations that were computed using the macroseismic data
and the associated focal mechanisms of earthquakes with Mw ≥5:7. The surprising
accuracy of the macroseismic orientations obtained using this method could in some
cases allow the true fault to be inferred between the two conjugate planes of a given
focal mechanism.
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