| The infrastructure constructions in western China make strategic sense in west development,national defense security,maintaining security and stability in border areas and rescue and relief work.The building sites of infrastructure constructions are limited,and the infrastructure constructions are built among the mountains generally which suffer from destructive earthquakes frequently and are located in complex hill topography.Under the earthquake,the ground motion of mountainous areas has significant hill topography effect and behaves abnormally,which threatens the security of the infrastructure constructions.Thus studying the regularity of the ground motion plays an important role in sites selection and seismic design for the infrastructure constructions.The sites of infrastructure constructions in mountainous area are controlled by several faults.In the area,the angle between fault strike and mountain strike and the distance from the site to fault vary greatly.The infrastructure constructions in mountainous areas often require the completion of large amount of excavation and filling,and forms high fill.Introducing the spectral-element method used in seismic wave propagation in three dimensional and setting up three-dimensional hill topography model,seismic wave propagation caused by reverse fault(Mw=6.0)in mountain area was simulated.Studying the influence of the angle between fault strike and mountain strike and high fill on the ground motion under near-field condition,calculating the influence of epicentral distance on the ground motion and analyzing the critical condition between near-field condition and far-field condition,the achievements are as follows:(1)In the condition that the depth of hypocenter and epicentral distance are 15 km and 22 km respectively,when fault strike is parallel to mountain strike:Comparing the source-proximal hillside with source-distal hillside,the seismic precautionary intensity of the latter may be higher in one degree.With the angle between fault strike and mountain strike ranging from 0 to ?/2,the seismic precautionary intensity of slope may decrease in one degree.On source-proximal hillside,the overall level of reduction factors reduces,and the lowest level of reduction factor maintains 0.5 approximately.On source-distal hillside,when the angle is ?/6,the overall level of amplification factors reach highest,and the highest level in slope is always over 1.6.(2)In the condition that the ratio between epicentral distance and focal depth?l/h<<,when fault strike is parallel to mountain strike,the mountain is in near field.In the ranges of ?l/h>5,the mountain is in far field.When the mountain is in near field,the overall level of PGA in source-proximal hillside is lower than that in other hillside.The PGA of source-proximal hillside is shrunk obviously,while the PGA of other hillside is amplified obviously,and the amplification factor can reach 1.7.The maximum PGA of slope appears near the middle of source-distal hillside.When the mountain is in far field,the PGA of slope is shrunk,and maximum PGA of slope appears at the top of mountain.On the contrary,the PGD is amplified obviously,and its amplification factor can reach 1.7.(3)When fault strike is parallel to mountain strike,in the condition that the depth of hypocenter and epicentral distance are 15 km and 30 km respectively,the high fill and the changes of its position have significant influence on the ground motion.There are high response level and amplification factor in high fill slope,especially at its toe.The seismic precautionary intensity of hillside may decrease in one degree.As an example,when high fill is on source-proximal hillside,the highest level of response and amplification factor in slope are 30%and 20%higher than that when high fill does not exist.When high fill is on source-proximal hillside,the level of response on high fill slope is higher,and the highest level of response near the high fill slope toe is 50%higher than that when high fill on other hillside. |
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