Archaeoseismology and Palaeoseismology in the Alpine ... - Tierra

are of lower slip‐rates (Pollino 0.3 mm/yr; Volturara 0.3
mm/yr).
Sensitivity Analysis
A sensitivity analysis was carried out to determine the
way different isoseismal dimensions influence the shaking
frequency maps. As a result, a new shaking frequency
map has been constructed by increasing the dimensions
of isoseismal IX from a 12.5 km radius to a 20 km radius
(Fig.3); which is an extreme upper value for a Ms=6.5
earthquake in the southern Apennines.
Fig.3 :Map showing how many times a locality receives enough
energy to shake at intensities ≥IX in 18 kyrs, assuming
homogenous bedrock geology, a circular pattern of energy
release and a 20 km radius of isoseismal IX which is an extreme
upper value for a Ms=6.5 earthquake in the southern Apennines.
By implementing larger dimensions for the intensity IX
isoseismals the affected area, as expected, has been
enlarged. In order to: i) quantify the differences in terms
of frequency of earthquake shaking between Figures 2
and 3, and ii) delineate how these differences are
distributed spatially; a third map has been constructed
and presented in Figure 4. In a few words, Figure 4 maps
the differences by subtracting the shaking frequency map
constructed with a 12.5 km radius of isoseismal IX from
the shaking frequency map constructed using a 20 km
radius of isoseismal IX. The highest difference is observed
in the area of the stepover between the Vallo di Diano
and the Maratea faults, where more than 50 additional
events (up to 58) are calculated (Fig. 4). This is a
substantial ten fold increase between the hazard map
constructed using a 12.5 km radius of isoseismal IX and
the map constructed with a 20 km radius of isoseismal IX.
When applying a 20 km radius, each isoseismal occupies
156% more area compared to the area covered by a 12.5
km radius isoseismal (1256 km 2 instead of 491 km 2 ).
However, there is only a 75% increase in the maximum
frequency value (63 instead of 36). Hence, it should be
noted that this increase of frequency values is not
distributed uniformly in the study area. For example, in
the stepover of the Vallo di Diano and the Val' D' Agri
1 st INQUA‐IGCP‐567 International Workshop on Earthquake Archaeology and Palaeoseismology)
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faults, there is almost a ten fold increase (1000%) in
frequency values, whereas in other areas such as the
hangingwall centres of the Val' D' Agri, the Monte Alpi
and the San Gregorio faults there is only a 10‐25%
increase. Therefore, it is clear that the hazard pattern is
modified in a non‐spatially uniform way so that the 156%
increase of the area affected from a single isoseismal can
not be extrapolated uniformly to the entire map.
Fig.4: Map showing the frequency differences between Fig. 2
and 3 by subtracting the hazard map constructed with a 12.5 km
radius from the hazard map using a 20 km radius of isoseismal
IX.
THE ESI 2007
Traditional intensities from which attenuation laws are
extracted are based on human parameters. However,
when using the effects on man and manmade
environment to assess the macroseismic intensity, then
intensity will tend to reflect mainly the economic
development and the cultural setting of the area that
experienced the earthquake, instead of its “strength”
(Serva, 1994). The Earthquake Environmental Effects (EEE)
are not influenced by human parameters as the
traditional intensity scales (MCS, MM, EMS 1992, etc)
predominantly imply. The ESI 2007 provides a
quantitative analysis and description of the EEE offering a
more credible documentation and has already been easily
applied in several events worldwide (Lalinde and Sanchez,
2007, Papathanassiou and Pavlides 2007, Serva et al.,
2007, Papanikolaou et al., 2009). Among other
advantages this scale: i) allows the accurate assessment
of intensity in sparsely populated areas, ii) provide a
reliable estimation of earthquake size with increasing
accuracy towards the highest levels of the scale, where
raditional scales saturate and ground effects are the only
ones that permit a reliable estimation of earthquake size
and iii) allows the comparison among future, recent and
historical earthquakes (Michetti et al., 2004).