Archaeoseismology and Palaeoseismology in the Alpine ... - Tierra

adius and the second is within a 50–100 kilometer radius
(Fig. 1). The NE1 fault, 13.7 kilometers northeast of the
site and Takht‐e‐Solayman fault, 43.5 kilometers
southwest of the site are examples of the first group. The
small‐scale seismotectonic maps do not indicate another
active fault within a 50‐kilometer radius of the site. The
Soltaniyeh and Zanjan faults in the southeast, Masouleh
and Sangavar faults in the northeast, northern and
southern Bozqoush faults in the north and the North
Tabriz fault in the northwest of the site area are amongst
the faults of the second group. It is important to point out
that the seismic activities of these faults based on the
historical and 20 th century earthquakes are confirmed.
Fig. 1: Faults location at the periphery of the site on the Land Sat
satellite image
The first group faults are within a 50‐kilometer radius of
the site and if they are active, with the considerable
length and appropriate distance to the site could impose
considerable acceleration to the dam and the power plant
structure. Due to the importance of this issue, the field
visits are conducted with the aid of large‐scale geological
maps and satellite images in order to detect other faults
within the 50‐kilometer radius of the site. These studies
resulted in identification of several other faults with the
maximum lengths of 2 to 3 kilometers. They could be
considered as minor faults. They mostly have general
northwest–southeast and northeast‐southwest trends
complying with the direction of main stress in the region.
However, minor faults with other trends were also
observed.
Among the mentioned minor faults at the vicinity of the
Moshampa dam and power plant, four faults are relevant.
They have almost parallel trends extending from
northwest to the southeast at the southwest of NE1 fault
and at the northeast of the Moshampa project site. These
faults are called NE2, NE3 and NE4, respectively based on
their distance from the dam site (Fig. 2). As it was
mentioned earlier, NE1 fault is located at the northeast of
the site. It is along the direction of North Tabriz and
Soltaniyeh faults with the length of 38.7km. On the small‐
scale seismotectonic maps of Iran, this fault has been
shown without any specific name. The NE2 fault is located
4 kilometers from the site, which according to these
studies, has a length of 25km. The layers displacement
along this fault is quite visible on the satellite images. The
NE3 fault is 1000 meters northeast of the site with a
length of 16.5 km. The NE4 fault is 350 meters
downstream of the site with a length of 2km. The field
1 st INQUA‐IGCP‐567 International Workshop on Earthquake Archaeology and Palaeoseismology)
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visits indicate that NE3 & NE4 faults have affected the
layers of upper red formation.
Fig. 2: A view of the faults at the vicinity of the site
SEISMOTECTONIC SPECIFICATION OF THE STUDIED AREA
The conducted seismotectonic studies point out that the
region around the Moshampa site (within 40‐kilometer
radius) had no seismic activity during the 20 th century and
the earlier centuries. This conclusion is based on the data
collected from several seismic centers as ISC, IIEES, and
BHRC. Albeit a great number of these earthquakes
occurred in the Azerbaijan, Alborz and northwestern part
of Zagros seismotectonic zones within the 300‐kilometer
radius of the site. In light of the seismic characteristics of
the Central Iran seismotectonic zone, the return period of
earthquakes in this province is higher and its magnitude is
greater than the Zagros & Alborz–Kopehdagh zones. The
above‐mentioned fact is to be taken into account,
although the project site and its 40‐kilometer radius have
never possessed seismic activity during the 20 th century
and the centuries before that. Due to the seismic nature
of Central Iran, it is possible that the region could
experience strong earthquakes in near future. Thus, for
the estimation of maximum seismic parameters of earth
movement, all the parameters related to the site are
taken into consideration.
The statistical study of the earthquakes around the
Moshampa site indicates the followings:
- 34 historical earthquakes with the magnitude of over
Ms5 are recorded at the periphery of the site, which
the closest took place (50 kilometers away) in 1880
with the magnitude of Ms5.6.
- During 1900 to 1962, only 12 earthquakes with the
magnitude of over Ms5 occurred within a 300‐
kilometer radius.
- The greatest earthquake took place in 1990 with the
magnitude of Ms7.4 at a distance of 158 kilometers
from the site.
- The closest earthquake (in the 20th century)
happened in 1903 with the magnitude of Ms5.6,
about 40 kilometers from the site.
The return period of earthquakes are calculated in this
study via three methods of Gutenberg‐Richter, Final Value
Fitting (Gumble & Hovel function), and Kijko‐Selevol
within a 300‐kilometer radius from the Moshampa dam
and power plant site. It seems that the calculation of
historical earthquakes makes the results of Kijko‐Selevol
method more accurate and more reliable. According to