Archaeoseismology and Palaeoseismology in the Alpine ... - Tierra

1 st INQUA‐IGCP‐567 International Workshop on Earthquake Archaeology and Palaeoseismology
Fig. 3: The logic tree of Sintubin & Stewart (2008), as applied to the Roman ruins of Baelo Claudia. The resulting overall
probability of our preferred end solution is 0.12, the archaeoseismlogical quality factor (AQF) computes to 0.95. SPF means
site potential factor and represents an interim result, taking into account the site conditions only.
THE ATAKAN LOGIC TREE ON PALAEOSEISMOLOGY
In contrast to Sintubin and Stewart (2008), Atakan et al.
(2000) created a logic tree that addresses
palaeoseismological investigations (Table 1).
Nevertheless, especially the first three criteria are
comparable and its structure in total was the model for
the archaeoseismological approach. Instead of the SCL,
another criterion Cri was proposed in 2000, here
corresponding to the relative level of importance of a
certain study. The palaeoseismic quality factor PQF can
finally be calculated by PQF = Pes x C ri.
The UNIPAS V3.0 program is designed to automate the
calculations and to help with QWF adaption. It can be
downloaded from the webpage of Bergen University
(http://www.geo.uib.no/seismo/software/unipas/unipas1
.html). For the following evaluation we only considered
palaeoseismological information available.
1. Tectonic setting and strain‐rate
As this criterion is similar to the one of the Sintubin logic
tree, we also choose a QWF of 0.95.
2. Site selection for detailed analysis
Prior to detailed palaeoseismological investigation, GPR
and geoelectrical measurements have been carried out to
find a suitable trenching site. In addition,
geomorphological analyses and geological mapping were
applied. Due to the complicated topography, the range of
available sites was very narrow. This leads to a relatively
low QWF of 0.78.
3. Extrapolation of the conclusions drawn from the
detailed site analysis to the entire fault
Our trenches all were close to each other and therefore
do not cover an area large enough to be representative
for the entire fault. We assume a QWF of 0.2.
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4. Identification of individual palaeo‐earthquakes
From a mere palaeoseismological point of view without
the archaeoseismological data from the ruins, the
identification of certain events was not possible.
Nevertheless, phenomena like slickensides, lineaments,
offset soils, ruptured pebbles, rockfalls, and landslides
patterns strongly point to local neotectonic activity in the
area. The appropriate QWF is 0.5.
5. Dating of palaeo‐earthquakes
No direct dating has been taking out at the trenching
sites, only the geomorphological analyses and
correlations give a rough time frame. This results in a
poor QWF of 0.25.
6. Palaeo‐earthquake size estimates
From primary and secondary evidences like seismic‐
triggered landslides and rockfalls, fault length analysis,
liquefaction phenomena etc. we estimated a minimum
magnitude of MW>5.5 for any event whose traces have
been found. The QWF here is 0.5.
From the single QWF values the PQF results to 0.0093. As
the date will be used to complete the local earthquake
catalogue, we assumed a Cri of 3. The overall PQF is 0.056
(Fig. 4).
COMPARISON, DISCUSSION AND CONCLUSIONS
For archaeoseismology we can compare our results to the
Sagalassos case study of Sintubin and Stewart (2008) only.
Given that their AQF is lightly lower than in our case,
Baelo Claudia mainly benefits from its geological setting,
not from the structural data.
Regarding the logic tree for palaeoseismology, our value
is twenty times lower than the one computed on the Bree
Fault example of Atakan et al. (2000) in Belgium, mainly
due to the low possibility of extrapolating the trench
observation to the entire fault, to the ambiguous