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These results are confirmed by physical effects on the building structures in the region
(field measurement on houses, measurement by Bilal and Ammar 2004, unpublished
data). They can be taken as an average value for the movement rate repartition in the
whole territory.
For an earthquake of a given intensity, defined by the value of the Magnitude (in Richter),
the action on a builded structure, which result in the greatest number of casualties, depends
from two sets of parameters: the characteristics of the structure itself and the nature of the
ground on which it is built. Several equations are proposed to relate all these variables
(Bojoroque and DeRoeck 2007, Ozkan 1998). The Syrian code (2004), used in this work is
based on the following equations:
Z= V/ IKCSW
(1)
C=1/T
(2)
T ~ 0, 1N (3)
Where V is the horizontal shear force, I correspond to the type and geometry of the structure
(bridges, tunnels, towers, dams, etc.), K the inelasticity coefficient of the structure, C the
dynamic coefficient, linked to the nodes propagation period (T), and the number of stages
(N), S a coefficient relative to the soil, and finally, W the total weight.
This seismic acceleration coefficient (Z) is a critical parameter. Estimated in cm /s2, it
describes the reaction of an object -structure in a limited zone -to an earthquake of a given
intensity. Its value changes from region to other after the upon seismic parameters, and so in
the same region according to the estimated parameters values, from 0 to a variable value,
reaching 1, 5 cm /s2 (Bojoroque and DeRoeck 2007).
For the dams Z is estimated, in Japan, at 0, 1- 0, 12 for weak earthquake zones, and 0, 15 for
strong zones. It is taken between 0, 05 and 0, 20 in Turkey, and between 0, 03 and 0, 24 in
India (Bilal 2009). A coefficient of 0, 1 indicates that a building is designed so that 0, 1 of its
weight can be applied horizontally during an earthquake
In Syria Z ranges between 0 and 0,25, depending on the region.It is 0,25 in Al Ghab region,
0,12 in Palmyra, and 0,05 - 0,1 in Deir Zour, in the East.
4.2.2 Seismicity-time analysis
The repetition of an earthquake (frequency return period of an earthquake in the same
locality), namely the seismic cycle is controversial (King 2004, Maderiaga 2004). However if
an earthquake is unique for a given locality, the distruction of earthquake activity with time
is of major importance.
Therefore, the historical record of ancient earthquakes has been investigated. Only were
used these verified by different sources (Taher 1979, Al Tarazi 1999). Available historical
data covers a wide period with variable magnitude: Ancient time between 750 and
1800,with magnitude estimated at 7.5-6.5 (Meghraoui 2003), it becomes 6 - 5 between 1800 -
2000 (UNISCO 1983,Stiro1992,Sbeinati and Darawcheh 1992,Al Tarazi1999),less than 5 for
the period of 1960 to 2000 and between 4,9-4 at present (USGS 1999). The results are
represented by the histogram of figure (10).They show that the seismic intensity tends to
decreases with time, in agreement with recent estimates on the movement rate (Le Beon
2008).
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