Archaeoseismology and Palaeoseismology in the Alpine ... - Tierra

THE ESTIMATION OF SEISMIC PARAMETERS
The pertinent data and information including the
mechanism of the faults, the appearance and the
geometry of the faults and the seismotectonic
specifications of the studied area are to be considered in
this method. In this regard, the North Tabriz, Bozqoush,
Masouleh, Soltaniyeh, Takht‐e‐Solayman, Zanjan and NE1
faults were evaluated. With reference to the magnitude,
geometrical specifications and the measured distances of
the seismic line sources at the periphery of the site with
the aid of reliable attenuation equations, the maximum
horizontal and vertical acceleration amounts for the 50%
and 84% levels were calculated. Eventually based on the
measured parameters calculated by the various
attenuation equations with the aid of the logic tree, the
NE1 fault was considered as the most important seismic
line source at the vicinity of the Moshampa dam and
power plant site. Moreover, the acceleration values
resulted from its reactivation is recommended to be used
as the maximum credible earthquake parameters (MCE)
for 50% and 84% levels (Table 1).
Table 1: Maximum credible earthquake accelerations
Fault Name
PGHA(g) PGVA(g)
H50% H84% V50% V84%
NE1 0.28 0.43 0.19 0.33
The analysis of seismic risk via the probabilistic method
comprises of the relationship between the strong earth
movement parameters and the possibility of their
occurrence at the project site within a specific time period
with the aid of mathematical and probabilistic methods.
The most important criterion in the aforesaid method is
to have access to reliable statistical data of the previous
earthquakes in the region. In this study, the point and line
seismic sources models were utilized and the tectonic
specifications of the site, logic tree method and
engineering judgment of maximum horizontal and vertical
acceleration parameters at the Moshampa project site for
design basic and maximum design earthquakes were
recommended (Table 2). Finally, it should be pointed out
that due to the tectonic specifications of the Moshampa
project site and the conducted studies, the values
calculated for the 50% and 84% level are recommended
for the final values.
Table 2: Seismic design parameters for Moshampa site
Earthquake
Design Levels
Return
Period
(year)
1 st INQUA‐IGCP‐567 International Workshop on Earthquake Archaeology and Palaeoseismology)
Maximum Value of
Acceleration (g)
50% 84%
V H V H
DBE 1000 0.11 0.16 0.19 0.25
MDE 1500 0.14 0.19 0.23 0.29
CONCLUSIONS
This article aims at explaining the importance of tectonic
and paleseismic studies at the vicinity of vital structures,
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which shows to have no connection with the seismic point
and line sources at the first glance. If only the
seismotectonic data of the site’s periphery has been
evaluated for the activities of the faults, in other words,
the relationship between the faults, historical and the 20 th
century epicenters as well as the impact of the faults on
the recent sediments have been analyzed, definitely the
Takht‐e‐Solayman fault would have been considered as
the most important seismic source. Subsequently, the
parameters of the earth’s strong movements for the
maximum credible earthquake (84% level) for the
horizontal and vertical values would have been 0.17g and
0.11g, respectively. These values are much smaller than
the results obtained from the point sources, which were
calculated for the return period of 10000 years
(equivalent to the MCE return period) for the 84% level,
horizontal value of 0.45g and vertical value of 0.36g.
While the tectonic and paleseismic studies revealed that
the NE1 fault segment is the most important seismic
scenario at the periphery of Moshampa dam and power
plant site. Although no earthquake in relation to the NE1
fault or within the 40‐kilometer radius of the site has
been recorded in the 20 th century, this study concludes
that the tectonic conditions and the location of the
Moshampa dam and power plant site indicates that in the
near future (during the normal life time of the structure)
the occurrence of a relatively strong earthquake at the
periphery of the Moshampa site is highly probable.
Acknowledgements: We would like to express our
appreciation to Mr. Samani for accompanying in field
geology and Mr. Karimi‐Haghighi for editing the paper.
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