近水平岩层阶状斜坡地震动响应特征分析

ANALYSIS OF SEISMIC RESPONSE TO GENTLE STEPPED ROCK SLOPE

川南中低山地区近水平岩层侵蚀台地阶状斜坡普遍发育且主要为居住区,研究这类阶状斜坡的地震动响应对揭示珙县地区震后崩塌山体灾害发育的动力机理有一定意义。宜宾地震后余震频发,安置在珙县五同村斜坡不同位置的强震监测仪于2020年9月6日成功监测到M_(S)3.1级余震,通过各监测点之间实测地震动数据相应的比较发现:与位于一级台阶处的参考监测点相比,二级台阶上的监测点在地震荷载作用下的地震动峰值加速度(PGA)和Arias强度放大系数、岩性共振周期比值均大于1.00,说明特殊斜坡具有较为显著的地震动高程放大效应和岩性选频放大效应;由于陡崖附近节理、裂隙较为发育,二级台阶中后部监测点地震动PGA、Arias强度比同台阶近陡崖监测点缩小了1.73、2.20倍,表明阶状斜坡存在近陡崖效应;二级台阶中后部(凸起地形)地震动持时是一级台阶参考监测点(凹陷地形)地震动持时的1.25倍,阶状斜坡存在微地形地震动持时放大效应。

It is of great significance to analyze the seismic shaking conditions of coseismic rock avalanches in Gong County area.The area is just located in gentle stepped rock slope of hilly area of south Sichuan Province.A set of seismic stations,located into Wutong village of Gong County,captured a M_(S)3.1 earthquake.Based on the captured seismic data,a series of analysis are carried out.The results show the upper stepped rock mass can produce larger site amplification and resonance amplification than the lower stepped rock.Due to the development of fissures and joints in cliff,the PGA and Arias of inner section of the upper stepped rock reduced 1.73 and 2.20 compared to the cliff section.This indicates that cliff exists site amplification effect.The seismic duration of the inner section of the upper stepped rock(convex terrain)is 1.25 times of the referred point(the lower stepped rock and the concave terrain).This indicates that micro topography has seismic duration amplification.