تحليل لرزه زمين ساخت و خطر زلزله در محدوده شهرهاي دزفول و شوش

Seismotectonic and seismic hazard analysis in Dezful and Susa cities

در اﯾﻦ ﺗﺤﻘﯿﻖ وﺿﻌﯿﺖ ﻟﺮزهزﻣﯿﻦﺳﺎﺧﺖ و ﺗﺤﻠﯿﻞ ﺧﻄﺮ زﻣﯿﻦﻟﺮزه ﺷﻬﺮﺳﺘﺎنﻫﺎي دزﻓﻮل و ﺷﻮش ﺗﺎ ﺷﻌﺎع 50 ﮐﯿﻠﻮﻣﺘﺮي ﻣﻮرد ﺗﻮﺟﻪ ﻗﺮار ﮔﺮﻓﺘﻪ اﺳﺖ. اﯾﻦ ﻣﻮﺿﻮع ﻣﯽﺗﻮاﻧﺪ ﺑﻪ اﯾﻤﻦﺳﺎزي ﺳﺎزهﻫﺎي ﻣﻬﻢ و ﺣﯿﺎﺗﯽ و ﻣﮑﺎنﯾﺎﺑﯽ ﻣﻨﺎﺳﺐ ﺗﺎﺳﯿﺴﺎت و ﺳﺎزهﻫﺎي ﺟﺪﯾﺪ در ﺳﻄﺢ اﯾﻦ ﺷﻬﺮﺳﺘﺎنﻫﺎ ﮐﻤﮏ ﮐﻨﺪ. ﺑﻪ ﻫﻤﯿﻦ دﻟﯿﻞ در اﯾﻦ ﺗﺤﻘﯿﻖ ﺑﺎ ﺑﺮرﺳﯽ ﺷﺮاﯾﻂ زﻣﯿﻦ ﺷﻨﺎﺳﯽ ﻣﻨﻄﻘﻪ اﻗﺪام ﺑﻪ ﺷﻨﺎﺳﺎﯾﯽ ﮔﺴﻞﻫﺎي ﻣﺤﺪوده ﻣﻄﺎﻟﻌﺎﺗﯽ و ﺗﻌﯿﯿﻦ اﺑﻌﺎد و ﻫﻨﺪﺳﻪ آﻧﻬﺎ ﺷﺪه اﺳﺖ. ﻫﻢﭼﻨﯿﻦ، ﭘﯿﺸﯿﻨﻪ ﻟﺮزهﺧﯿﺰي اﯾﻦ ﻣﻨﻄﻘﻪ ﻣﻮرد ارزﯾﺎﺑﯽ ﻗﺮار ﮔﺮﻓﺖ. در اﯾﻦ ﻣﻘﺎﻟﻪ ﺑﺮآورد ﭘﺎراﻣﺘﺮﻫﺎي ﺟﻨﺒﺶ زﻣﯿﻦ ﺑﻪ روش آﻣﺎري-اﺣﺘﻤﺎﻻﺗﯽ و در ﺳﻄﻮح اﺣﺘﻤﺎل وﻗﻮع ﻣﺨﺘﻠﻒ اﻧﺠﺎم ﺷﺪه اﺳﺖ. ﻧﺘﺎﯾﺞ ﻧﺸﺎن ﻣﯽدﻫﻨﺪ ﮐﻪ ﺑﯿﺸﯿﻨﻪ ﺑﺰرﮔﯽ زﻟﺰﻟﻪ ﻣﺒﻨﺎي ﻃﺮح )اﺣﺘﻤﺎل 64 درﺻﺪ( ﺑﺮاي دوره ﻫﺎي ﺑﺎزﮔﺸﺖ 100 ،50 ،25 و 200 ﺳﺎﻟﻪ در اﯾﻦ ﻣﻨﻄﻘﻪ ﺑﺘﺮﺗﯿﺐ 5/9 ،5/6 ،5/4 و 6/1 رﯾﺸﺘﺮ ﺑﺮآورد ﺷﺪه اﺳﺖ. ﻧﺘﺎﯾﺞ ﺣﺎﺻﻞ از راﺑﻄﻪ ﻣﯿﺮاﯾﯽ داﻧﻮوان ﻣﻮﯾﺪ آن اﺳﺖ ﮐﻪ ﺑﯿﺸﯿﻨﻪ ﺷﺘﺎب ﻗﺎﺑﻞ اﻧﺘﻈﺎر و ﻣﺒﻨﺎي ﻃﺮح ﺑﺮاي ﺷﻬﺮ دزﻓﻮل ﺑﻪﺗﺮﺗﯿﺐ 0/22 و g 0/33 اﺳﺖ. اﯾﻦ ﻣﻘﺪار ﺑﺮاي ﺷﻬﺮ ﺷﻮش ﺑﺘﺮﺗﯿﺐ 0/24 و g 0/36 اﺳﺖ. ﻧﻘﺸﻪﻫﺎي ﭘﻬﻨﻪﺑﻨﺪي ﺗﻬﯿﻪ ﺷﺪه ﻣﺒﯿﻦ آن اﺳﺖ ﮐﻪ ﺑﺨﺶﻫﺎي ﺷﻤﺎﻟﯽ و ﻣﯿﺎﻧﯽ ﮔﺴﺘﺮه ﻣﻮرد ﻣﻄﺎﻟﻌﻪ از ﺑﯿﺸﺘﺮﯾﻦ ﺧﻄﺮ ﺑﺮﺧﻮردار ﻣﯽ ﺑﺎﺷﻨﺪ. ﺑﻨﺎﺑﺮاﯾﻦ، ﺑﺎﯾﺪ ﻧﺴﺒﺖ ﺑﻪ ﻣﻘﺎومﺳﺎزي و ﺗﻘﻮﯾﺖ ﺑﺎﻓﺖﻫﺎي ﻓﺮﺳﻮده و ﺗﺎرﯾﺨﯽ اﻗﺪام ﻧﻤﻮد

The construction of earthquake-resistant engineering projects and the stability evaluation for existing buildings are a crucial issue in seismic areas. The response of constructions and their damages depend on source parameters and distance to rupture, amplitude, duration, the spectral content of vibration and local conditions of the site (soil conditions, topography, etc.; Jorjiashvili et al., 2016; Ashayeri et al., 2018). An earthquake not only destructs directly critical structures by generating the seismic waves, but also leads to geohazards such as liquefaction, settlement, sand boiling, and the turbidity of spring and well waters. In such seismically active regions, the seismic hazard analysis is inevitable. The process of assessing the design parameters of seismic ground motion is called seismic hazard analysis. Probabilistic seismic hazard analysis (PSHA) is one of the most practical approaches for quantify uncertainties about future earthquake parameters and combine them to produce an explicit description of the distribution of future shaking that may occur at a site (Backer, 2013). The method is based on the rate of a past earthquake determined from the earthquake catalog. Dezful and Shush cities are historical and second population areas in Khuzestan province. On the other hand, the presence of different faults in the region demonstrates the necessity for seismic study and risk assessment of this area. This research focuses on seismotectonic setting and seismic risk analysis of Dezful and Susa cities using the probabilistic method for 50 km radius. 2- Research methods In order to assess seismic hazards for a particular region, all possible sources of seismic activity must be recognized. For these purposes, geological investigations, and recognition of faults, as well as their geometry in the study area carried out. In this paper, the seismic sources were identified as line sources based on geological and seismotectonic investigations for the study area. Moreover, the seismic background of these cities evaluated. The primary seismic sources in the region are faults such as Lahbari, Dezful, Cheshmeh Khosh, Pir Ahmad, and Balarud fault zone as well as NS1 and NS2 basement faults. Also, all instrumented earthquakes were gathered in the region covering a radius of 50 km keeping Dezful city as the center from the International Institute of Earthquake Engineering and Seismology (IIEES), Iranian Seismological Center (ISC), and the United States Geological Survey (USGS). In the next step, the maximum credible earthquake (MCE) and design base earthquake (DBE (for the various hazard levels measured. Finally, peak ground acceleration of the area for the hazard levels of 10 and 64% exceedance probability within 50 years calculated. Then, hazard maps of peak ground accelerations were delineated for the selected area.