The Research On Micro-tremor Characteristics And Dynamic Response On Sites With Ground Fissures

Ground fissures is a serious geological disasters in many countries of the world. It has become one of the major geological disasters of slow-change type worldwide. So far, research about ground fissures’ character of distribution, character of activity and mechanism of cause and prevention measures has achieved a lot, but the research about the site dynamic effects is rare, Particularly about the dynamic effects of reginal ground fissures group is still blank. Xi’an is a typical region with both intensively developed ground fissures and high seismic hazard level in our country. So it has important theoretical and practical significance for similar construction disaster prevention and mitigation in Xi’an to study the dynamic effects of group ground fissures.This paper focus on the research on F5-F9 ground fissures in Xi’an to study the dynamic effects of group ground fissures by means of field investigation and situ microtremors tesing. It reveals the influence of peak and corresponding predominant period in dynamic effects of group ground fissures. We discover the character of amplification effect and corresponding scope of influence in dynamic effects of group ground fissures too. We also put forward some seismic levels and avoidance distance. Through the research we found that:1.The predominant period is basically the same in tableland of two, three and four terrace. The respective average of testing is 0.38 s, 0.38 s, 0.37 s. Corresponding predominant period is 2.64 Hz, 2.64 Hz, 2.69 Hz. At the same time, in the same predominant period of the same ground fissure, the fissure trend alone vertically has no significant variation.2.The upper soil layer’s overall performance of ground fissures appeals to be more than the lower part’s in Xi’an. At the same time, alone vertical trend of the fissure, the amplitude decreases while the distance from ground fissure increases. Butthe lower part’s decreases slowly. The amplitude is similar in different ground fissure sites, but quite different while it is in different terrace. The four terrace is maximum, the three terrace followed, and the two terrace minimum. It shows that amplitude to the site soil structures, especially soft overburden thickness is closely related. While the thickness of the cover layer is greater, the amplitude is greater.3.Near the fissure area, ground fissure’s amplitude has Amplification effect, and the upper’s amplification factor performance better than the lower soil layer’s. Meanwhile, alone the vertical trend, amplification factor increases while the distance decreases. The pulsationamplification factor is similar in the same terrace and quite different while the terrace changes. The two terrace is maximum, the three terrace followed, and the four terrace minimum. It can conclude that more soft the soil structure, the larger the thickness of the cover layer, the less obvious the amplification effect.4.Considering the amplitude of ground fissures site and the variation character ofamplificationfactor in the direction perpendicular to the fissure trend alone distance.It can be found the upper soil layer’s scope of influence caused by the dynamic response of ground fissure to site is slightly larger than the lower soil layer’s. From the view of engineering avoidance or increasing the the level of seismic protect level, the upper soil layer’s scope can be taken as 40 m, the lower as 35 m.