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Ta b l e 2 Late medieval earthquakes with I o >
VI (EMS-98) obtained as a result of the review. Lat
N
=
latitude north, Lon E
=
Longitude east, Q e =
quality of epicentre, I o =
epicentral intensity,
Q i =
quality of I o . Quality indexes are explained in the text (Section 2)
Date
Time
Lat N
Lon E
Q e
I o
Q i
1373.03.03
1-2
42 38
0 41
D
VIII-IX
C
1427.03.13
11
42 02
2 35
C
VI-VII
C
1427.03.19
21
41 59
2 35
B
VIII
C
1427.04.22
22
41 59
2 35
B
VI-VII
C
1427.05.15
15-16
42 10
2 26
B
VIII
C
41 51
2 49
1427.06.14
12
C
VII
C
42 18
2 20
1428.02.02
8-9
BIX
C
41 38
2 17
1448.05.25
1
C
VII-VIII
C
events. This assignment could be questionable but the authors think that there are not
consistent arguments to assign different quality indexes to the different earthquakes
considered as we are dealing with Middle Ages events for which the documen-
tary sources are quite different from those for Modern period. The information on
damages is, in general, not detailed enough and, moreover, is almost only referred to
singular buildings, namely castles, palaces, churches and monasteries, i.e. properties
of the king or the church. Detailed damages on dwellings are rarely reported. Under
these circumstances it is not possible to assign intensity properly using statistical
criteria according to the definitions of the Intensity scale. For this reason we keep
Qi
C for all events.
In order to complement the obtained macroseismic parameters (epicentre and
Io) which are the main goal of this study, hypocentral depth and magnitude have
been estimated for some of the events in Table 2, using the approaches described
in Section 2. Focal depth has been estimated from intensity decay curves using
Sponheuer model (see Section 2).
Figure 5 show the intensity data points for the March 3rd, 1373 earthquake. The
best fit to Sponheuer curve is obtained for
=
16 Km. Due to
the scarcity of data, in particular for the epicentral region, these values have low
reliability. On November 11th, 1923 an earthquake of intensity VIII (MSK) occurred
on the same area as that of 1373. For the 1923 event a large amount of intensity
data points are available and the best fit to Sponheuer curve were obtained for
0
.
001 and h
=
0
5 Km (Susagna et al. 1994). Comparison of the data from these two
earthquakes supports the hypothesis that the hypocentre of the 1373 event is deeper
than that of 1923.
Figure 6 shows the intensity decay curve for the February 2nd, 1428 earthquake.
As it can be seen comparing Figs. 5 and 6 the number of intensity data points for
1428 earthquake is much larger. The best fit to Sponheuer curve is obtained for
.
001 and h
=
obtained is in agreement with most
of the attenuation studies carried out in the Pyrenean region (Banda and Correig
1984; Levret et al. 1994; Susagna et al. 1994; Secanell et al. 2004).
Some magnitude estimates have been obtained for the earthquakes listed in
Table 2 using, depending on the available data, the various empirical relations
0
.
001 and h
=
9 Km. The lower value of
 
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