ﻨﻤﺫﺠﺔ ﺍﻟﻤﺤﺎﻜﺎﺓ ﺍﻟﺭﻗﻤﻴﺔ ﻭﺃﺜﺭﻫﺎ ﻓﻲ ﺘﺨﻔﻴﻑ ﺍﻟﻤﺨﺎﻁﺭ ﺍﻟﺯﻟﺯﺍﻟﻴﺔ
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ﻤﺠﻠﺔ ﺠﺎﻤﻌﺔ ﺩﻤﺸﻕ ﻟﻠﻌﻠﻭﻡ ﺍﻷﺴﺎﺴﻴﺔ ـ ﺍﻟﻤﺠﻠﺩ ( 20 ) ـ ﺍﻟﻌﺩﺩ ﺍﻟﺜﺎﻨﻲ ـ 2004 - ص 237 - 266 :
ﺭﻨﺩﺓ ﻤﺤﻤﺩ ﻭﻭﺍﺜﻕ ﺭﺴﻭل ﺁﻏـﺎ - ﻗﺴﻡ ﺍﻟﺠﻴﻭﻟﻭﺠﻴﺎ ـ ﻜﻠﻴﺔ ﺍﻟﻌﻠﻭﻡ ـ ﺠﺎﻤﻌﺔ ﺩﻤﺸﻕ :
ﺍﻟﻤﻠﺨﺹ
ﺘﻘﻊ ﺩﻤﺸﻕ ﻓﻲ ﺍﻟﺠﺯﺀ ﺍﻟﺠﻨﻭﺒﻲ ﻤﻥ ﺴﻭﺭﻴﺔ ﺒﺎﻟﻘﺭﺏ ﻤﻥ ﻨﻅﺎﻡ ﺼﺩﻉ ﺍﻟﺒﺤﺭ ﺍﻟﻤﻴﺕ ﻭﺨﺎﺼﺔ ﺼﺩﻉ ﺴﺭﻏﺎﻴﺎ ﺃﺤﺩ ﻓﺭﻭﻋﻪ ﺍﻟﻤﻬﻤﺔ . ﻭﻴﻌﺩ ﻫﺫﺍ ﺍﻟﺼﺩﻉ ﻨﺸﻁﺎ ﻭﻤﺼﺩﺭﺍ ﺯﻟﺯﺍﻟﻴﺎ ﻟﺯﻻﺯل ﻤﺩﻤﺭﺓ ﺍﺴﺘﻨﺎﺩﺍ ﺇﻟﻰ ﺍﻟﺩﺭﺍﺴﺎﺕ ﺍﻟﺤﺩﻴﺜـﺔ ﻭﺍﻟﺴﺠل ﺍﻟﺯﻟﺯﺍﻟﻲ ﺍﻟﺘﺎﺭﻴﺦ ﻭﺍﻟﺯﻻﺯل ﺍﻟﻤﺴﺠﻠﺔ ﺁﻟﻴﺎ .
ﻭﻟﻨﻤﺫﺠﺔ ﺍﻟﺤﺭﻜﺔ ﺍﻷﺭﻀﻴﺔ ﻓﻲ ﺴـﻬل ﺩﻤـﺸﻕ ﻭﺘﻘـﺩﻴﺭ ﺘﻀﺨﻴﻤﻬﺎ ﻁﺒﻘﻨﺎ ﺍﻟﻁﺭﻴﻘﺔ ﺍﻟﻬﺠﻴﻨﺔ ﺍﻟﺘﻲ ﺘﺠﻤﻊ ﺒﻴﻥ ﻁﺭﻴﻘﺘﻲ ﺍﻟﻤﺤﺼﻠﺔ ﺍﻟﺸﺭﻁﻴﺔ ﻭﺸﺒﻜﺔ ﺍﻟﻔﺭﻭﻗﺎﺕ ﺍﻟﻤﺤـﺩﻭﺩﺓ ﻋﻠﻰ ﻤﻘﻁﻊ ﺜﻨﺎﺌﻲ ﺍﻟﺒﻌﺩ ﻴﻤﺭ ﻤﻥ ﻤﺩﻴﻨﺔ ﺩﻤﺸﻕ، ﺇﺫ ﺘﺴﻤﺢ ﻫﺫﻩ ﺍﻟﻁﺭﻴﻘﺔ ﺒﺤﺴﺎﺏ ﺍﻟﺤﺭﻜﺔ ﺍﻷﺭﻀﻴﺔ ﻓـﻲ ﻭﺴـﻁ ﻤﺭﻥ ﻭﻏﻴﺭ ﻤﺘﺠﺎﻨﺱ ﻭﺒﺤﺴﺎﺏ ﺍﻟﺴﺠﻼﺕ ﺍﻟﺯﻟﺯﺍﻟﻴﺔ ﺍﻟﺼﻨﻌﻴﺔ ﻋﻠﻰ ﻁﻭل ﻫﺫﺍ ﺍﻟﻤﻘﻁﻊ ﺒﺘﺭﺩﺩ ﻗﻁﻊ ﻤﺴﺎﻭﻱ ﺇﻟﻰ 5 ﻫﺭﺘﺯ ﻟﻠﻤﺼﺩﺭ ﺍﻟﺯﻟﺯﺍﻟﻲ ( ﺼﺩﻉ ﺴﺭﻏﺎﻴﺎ ) ﺒﺎﻓﺘﺭﺍﺽ ﺯﻟﺯﺍل ﻗﺩﺭﻩ 6.5 ﻋﻠﻰ ﻤﻘﻴﺎﺱ ﺭﻴﺨﺘﺭ ﻨـﺎﺘﺞ ﻋـﻥ ﻫـﺫﺍ ﺍﻟﺼﺩﻉ .
ﻟﻘﺩ ﺘﻡ ﻭﻀﻊ ﺍﻟﻨﻤﻭﺫﺝ ﺍﻹﻗﻠﻴﻤﻲ ﻭﺍﻟﻤﻘﻁﻊ ﺍﻟﻤﺘﻐﻴﺭ ﻟﻠﺒﺭﻭﻓﻴل ﻤﻥ ﺍﻟﻤﻌﻁﻴﺎﺕ ﺍﻟﺠﻴﻭﻟﻭﺠﻴﺔ ﻭﺍﻟﺠﻴﻭﺘﻜﻨﻴﻜﻴﺔ ﺍﻟﻤﺘﻭﺍﻓﺭﺓ ﻋﻥ ﻤﻨﻁﻘﺔ ﺍﻟﺩﺭﺍﺴﺔ . ﻭﺠﺩﺕ ﺍﻟﻘﻴﻡ ﺍﻟﻌﻅﻤﻰ ﻟﺘﻀﺨﻴﻡ ﺍﻟﺤﺭﻜﺔ ﺍﻷﺭﻀﻴﺔ ﻓﻲ ﺴﻬل ﺩﻤﺸﻕ ﺒﺸﻜل ﻋـﺎﻡ ﻋﻠﻰ ﺍﻟﺘﺭﺩﺩﺍﺕ ﺯﻫﺎﺀ 1 ﻫﺭﺘﺯ ﻭ 4 ﻫﺭﺘﺯ . ﺇﻀﺎﻓﺔ ﺇﻟﻰ ﺫﻟﻙ ﺘﻤﺕ ﺩﺭﺍﺴﺔ ﺍﺤﺘﻤﺎل ﺤﺩﻭﺙ ﺘﻤﻴﻴﻊ ﻟﻠﺘﺭﺒﺔ ﻓﻲ ﺴﻬل ﺩﻤـﺸﻕ ﺍﻋﺘﻤـﺎﺩﺍ ﻋﻠـﻰ ﻁـﺭﻴﻘﺘﻴﻥ ﺇﺤﺩﺍﻫﻤﺎ ﺒﻨﺎﺀ ﻋﻠﻰ ﻤﻌﻠﻭﻤﺎﺕ ﻁﺒﻭﻏﺭﺍﻓﻴﺔ ﻭﺠﻴﻭﻟﻭﺠﻴﺔ، ﻭﺍﻟﺜﺎﻨﻴﺔ ﺒﻨﺎﺀ ﻋﻠﻰ ﺍﻟﻤﻌﻠﻭﻤﺎﺕ ﺍﻟﺠﻴﻭﺘﻜﻨﻴﻜﻴﺔ ( ﻗـﻴﻡ N ﻭﺍﻟﻘﻁﺭ ﺍﻟﺤﺒﻴﺒﻲ ) ﻭﻗﻴﻤﺔ ﺍﻟﺘﺴﺎﺭﻉ ﺍﻷﺭﻀﻲ، ﻭﺫﻟﻙ ﻤﻥ ﺃﺠل ﺤﺴﺎﺏ ﻤﻌﺎﻤل ﻤﻘﺎﻭﻤﺔ ﺍﻟﺘﻤﻴﻊ FL ﻭﻤﺅﺸﺭ ﻗﺎﺒﻠﻴـﺔ ﺍﻟﺘﻤﻴﻊ IL ﻓﻭﺠﺩﻨﺎ ﺃﻥ ﺍﻟﻤﺅﺸﺭ ﻴﺯﻴﺩ ﻋﻠﻰ ﺍﻟﻘﻴﻤﺔ 15 ، ﻭﻫﺫﺍ ﻴﺸﻴﺭ ﺇﻟﻰ ﺍﺤﺘﻤﺎل ﺤﺩﻭﺙ ﺍﻟﺘﻤﻴﻴﻊ .
ﺍﻟﻜﻠﻤﺎﺕ ﺍﻟﻤﻔﺘﺎﺤﻴﺔ : ﺴﻬل ﺩﻤﺸﻕ، ﺍﻟﻤﺤﺎﻜﺎﺓ ﺍﻟﺭﻗﻤﻴﺔ، ﺍﻟﺘﻤﻨﻁﻕ ﺍﻟﺯﻟﺯﺍﻟﻲ .
Numerecal simulation modeling and it’s impact in mitigation of seismological hazard «Case study-Damascus Plain»
R. Mohamad and W. Rasoul-Agha Department of geology - Faculty of Sciences- Damascus University
ABSTRACT
Damascus is located at the southern part of Syria not far from the Dead sea fault system, in particular from one of its branches the Sergayah fault. The latter in particular is a quite active fault system and the main seismic source for both destructive historical events felt and instrumental seismicity recorded in Damascus.
To model seismic ground motion in Damascus plain and to estimate its amplifications we use a 2-D hybrid method coupling modal summation with finite differences. This techniques allows to compute ground motion in laterally heterogeneous an elastic media. Synthetic seismograms with a cutoff frequency of 5 Hz are created along one 2-D profile passing through the city of Damascus for possible seismic source with assumed magnitudes around 6.5 located on the Sergayah fault.
The average regional structural model and the laterally heterogeneous parts of the profiles have been derived from detailed geological and geotechnical data available for the investigated area. From the computations we can infer that the maximum ground motion amplification values in Damascus plain are generally found at frequencies around 1 Hz and 4 Hz. In addition for assessing liquefaction potential in Damascus plain tow methods have been used. first one evaluated roughly liquefaction potential based on topographical and geological information and the second one based on geotechnical data such as N- value, grain size and estimated peak ground acceleration to calculate a liquefaction resistance factor, FL. and liquefaction potential index, IL. We found that IL exceeds 15 which mean probable sever liquefaction.
Key Words: Damascus plain, Numerecal simulation, Seismic Microzonation.
اﺴـﺘﻨﺘﺎﺠﺎﺕ
ﺒﺎﺴﺘﺨﺩﺍﻡ ﺘﻘﺎﻨﺔ ﻨﻤﺫﺠﺔ ﺍﻟﻤﺤﺎﻜﺎﺓ ﺍﻟﺭﻗﻤﻴﺔ ﻭﻁﺭﻴﻘﺔ ﺍﻟﺘﻘﺎﻨﺔ ﺍﻟﻬﺠﻴﻨﺔ ﻓﻲ ﺤـﺴﺎﺏ ﺍﻟـﺴﺠﻼﺕ ﺍﻟﺼﻨﻌﻴﺔ ﻟﻁﻴﻑ ﺍﻟﺘﺴﺎﺭﻉ ﻭ ﻁﻴﻑ ﺍﻟﺘﻀﺨﻴﻡ ﻭﻨﺴﺏ ﻁﻴﻑ ﺍﻻﺴﺘﺠﺎﺒﺔ ﻋﻠﻰ ﻁـﻭل ﺍﻟﺒﺭﻭﻓﻴـل AA ﻟﻸﻤﻭﺍﺝ ﺍﻟﺯﻟﺯﺍﻟﻴﺔ ﻟﻠﺤﺭﻜﺔ ﺍﻷﺭﻀﻴﺔ ﺍﻟﻨﺎﺠﻤﺔ ﻋﻥ ﺍﻟﻤﺼﺩﺭ ﺍﻟﺯﻟﺯﺍﻟﻲ ﺍﻟﻤﻔﺘﺭﺽ ﺼﺩﻉ ﺴﺭﻏﺎﻴﺎ ﺘﻡ ﺍﺴﺘﻨﺘﺎﺝ ﻤﺎ ﻴﺄﺘﻲ :
1- ﻴﺤﺼل ( ﺒﺸﻜل ﻋﺎﻡ ) ﺍﻟﺘﻀﺨﻴﻡ ﺍﻟﺭﺌﻴﺱ ﻟﻸﻤﻭﺍﺝ ﻋﻠﻰ ﺃﻁﺭﺍﻑ ﺍﻟﺤﻭﺽ ﺤﻴﺙ ﻴﻭﺠﺩ ﻋﺩﻡ ﺍﻟﺘﺠﺎﻨﺱ ﺍﻷﻋﻅﻤﻲ ﺒﻴﻥ ﺒﻨﻴﺔ ﺍﻟﺤﻭﺽ ﻭﺍﻟﻭﺴﻁ ﺍﻟﻤﺤﻴﻁ ﺒﻪ .
2- ﺘﻜﻭﻥ ﺍﻟﺘﺭﺩﺩﺍﺕ ﺍﻟﻤﺴﻴﻁﺭﺓ ﻓﻲ ﺍﻷﺠﺯﺍﺀ ﺍﻟﻌﻤﻴﻘﺔ ﻤﻥ ﺍﻟﺤﻭﺽ ﻗﺭﺍﺒـﺔ 1 ﻫﺭﺘـﺯ ﻭﻓـﻲ ﺃﻁﺭﺍﻑ ﺍﻟﺤﻭﺽ -3 4 ﻫﺭﺘﺯ .
3- ﺒﻠﻐﺕ ﺃﻋﻠﻰ ﻗﻴﻤﺔ ﻟﻠﺘﺴﺎﺭﻉ ﺍﻷﺭﻀﻲ ﺍﻟﻤﺤﺴﻭﺏ ﻋﻠﻰ ﺍﻟﺒﺭﻭﻓﻴل AA , 275 / ﺴﻡ ﺜﺎ2 ، ﻭﺃﻋﻠﻰ ﺘﻀﺨﻴﻡ 3.5-4 ﻋﻨﺩ ﺍﻟﺘﺭﺩﺩﺍﺕ ﻗﺭﺍﺒﺔ 3 ﻫﺭﺘﺯ ﻋﻠﻰ ﺒﻌﺩ ﺯﻫﺎﺀ 34 ﻜﻡ ﻤـﻥ ﺍﻟﻤـﺼﺩﺭ ﺍﻟﺯﻟﺯﺍﻟﻲ .
4- ﻴﺤﺘﻤل ﺤﺩﻭﺙ ﻅﺎﻫﺭﺓ ﺍﻟﺘﻤﻴﻊ ﻓﻲ ﺴﻬل ﺩﻤﺸﻕ ﺍﺴﺘﻨﺎﺩﺍ ﺇﻟﻰ ﻗﻴﻡ ﻤﻌﺎﻤل ﻤﻘﺎﻭﻤـﺔ ﺍﻟﺘﻤﻴـﻊ ﻭﻤﺅﺸﺭ ﺍﻟﺘﻤﻴﻊ ﺍﻟﻠﺫﻴﻥ ﺘﻡ ﺤﺴﺎﺒﻬﻤﺎ ﻓﻲ ﺃﺤﺩ ﺍﻟﻤﻭﺍﻗﻊ ﻓﻲ ﺴـﻬل ﺩﻤـﺸﻕ ، ﻭﻫـﺫﻩ ﺍﻟﻘـﻴﻡ ﺍﻟﺘﺄﺸﻴﺭﻴﺔ ﻻﺤﺘﻤﺎﻟﻴﺔ ﺤﺩﻭﺙ ﻅﺎﻫﺭﺓ ﺍﻟﺘﻤﻴﻊ ﻻﺒﺩ ﻤﻥ ﺃﺨﺫﻫﺎ ﺒﺎﻟﺤـﺴﺒﺎﻥ ﻭﻻ ﺴـﻴﻤﺎ ﺃﻨﻬـﺎ ﺘﻁﺎﺒﻘﺕ ﺒﻨﺴﺒﺔ 86 % ﻓﻲ ﺍﻟﻤﻭﺍﻗﻊ ﺍﻟﻤﺸﺎﺒﻬﺔ ﺍﻟﺘﻲ ﺘﻤﻴﻌﺕ ﺒﻔﻌل ﺍﻟﺯﻻﺯل ﻓﻲ ﺍﻟﻴﺎﺒﺎﻥ . ﻭﻻ ﻴﺨﻔﻰ ﻤﺎ ﻟﻬﺫﻩ ﺍﻟﻨﺘﺎﺌﺞ ﻤﻥ ﺃﻫﻤﻴﺔ ﺘﻁﺒﻴﻘﻴﺔ ﻓﻲ ﻤﻭﺍﺠﻬﺔ ﺍﻷﺨﻁﺎﺭ ﺍﻟﺯﻟﺯﺍﻟﻴﺔ ﺍﻟﻤﺘﻭﻗﻌﺔ .
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