Geoscience Reference
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information obtained is stored in a database that allows us to make consultations
combining different criteria, and facilitates the incorporation of new reports. This
also constitutes an excellent point of departure for subsequent studies.
For the first time it has been possible to undertake a joint analysis of all the docu-
mentation of the earthquakes of the late medieval period in Catalonia and to evaluate
these events using a homogeneous criterion. Our evaluation of the earthquakes is a
marked improvement on earlier studies in two respects: number and quality of the
descriptions, and homogeneity.
The cataloguing of historical earthquakes is of paramount importance especially
in areas where the rate of deformation is low as is the case of Catalonia. European
Macroseismic Scale 98 (EMS-98) (Grunthal 1998) has been used to assign intensity
at the different sites in order that historical earthquakes can be characterized with
parameters that are comparable to those of current earthquakes.
For a given earthquake a value of site intensity and an index of quality are as-
signed for each locality based on historian's criteria, type of documentary sources
and information that contain, including those referring the conditions of the build-
ings before the earthquakes (Olivera et al. 2006). Moreover, the earthquake macro-
seismic parameters (epicentre location and epicentre intensity Io) are associated
with an index of quality based on the criteria established by Lambert et al. (1996)
depending on the quality, density and geographical distribution of the intensity data
points. For the epicentre location: A - few km; B - around 10 km; C - between 10
and 20 km; D - between 20 and 50 km. And for the epicentral intensity: A - certain,
dense distribution, with precise maximum locality intensities; B - fairly certain, less
dense distribution, with precise maximum locality intensities; C - uncertain, sparse
distribution, with imprecise locality intensity values; D - fairly certain, derived from
an attenuation-law base calculation (Sponheuer); E - arbitrary, due to the sparseness
of locality intensities.
This paper focuses on the assessment of macroseismic parameters - epicentre
and epicentral intensity - to a set of medieval earthquakes through an intensive
and exhaustive review and analysis of historical documentary sources. However,
in order to have a preliminary estimate of seismic parameters other than location
and epicentral intensity, e.g. depth and magnitude, existing empirical relation can
be used.
In order to estimate focal depth, Sponheuer (1960) type intensity decay curves
have been adjusted to the observed intensity data points.
In order to estimate magnitude, the following approaches have been chosen
among many other available, to be applied:
(a) Empirical relations Imax - magnitude.
A classical proposal is that from Gutenberg and Richter (1954), given by M
=
2Io
1. For earthquakes in stable continental regions, Johnston (1996b) proposed
the following correspondence between Imax and moment magnitude Mw:
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3
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