CAJ | 학술논문

2008年汶川 MS 8.0强震中频繁出现断层穿越的地震滑坡，除发震断层的地震特性外，其自身场地效应也会影响斜坡动力响应，甚至加剧斜坡失稳。本文以汶川极震区绵竹九龙镇山前斜坡为典型实例，根据余震作用下斜坡不同高程实测地震记录及地脉动测试结果，通过单点谱比法（H／V），获得斜坡地震动加速度随高程的放大系数和地脉动的频谱特征曲线，通过曲线对比分析发现：1）斜坡两次典型余震 PGA 放大系数随高程先减小后增大，呈明显的“凹形”特征，“凹形”部位位于断层位置，其 PGA 放大系数约为斜坡底部测点0.4～1.0，坡顶测点的 PGA 放大系数则达到1.0～2.0倍。由于 PGA 放大系数是在断层位置出现的明显拐点，从地质上表明了断层场地效应明显；（2）各点 NS ／UD 谱比普遍大于 EW／UD 谱比。断裂区域卓越频率为低频1Hz，小于其他测点的频率，对应谱比最大值高达3.0～4.0，高于其他测点谱比最大值。说明地表破裂处岩土体松散破碎，导致断层处的卓越频率较低，近场余震传播过来的高频地震波被断层隔断，地震加速度放大系数在该处发生了衰减，场地效应显著。本研究有助于增强断层场地对斜坡动力响应影响的认识。
2008년문천 MS 8.0강진중빈번출현단층천월적지진활파，제발진단층적지진특성외，기자신장지효응야회영향사파동력향응，심지가극사파실은。본문이문천겁진구면죽구룡진산전사파위전형실례，근거여진작용하사파불동고정실측지진기록급지맥동측시결과，통과단점보비법（H／V），획득사파지진동가속도수고정적방대계수화지맥동적빈보특정곡선，통과곡선대비분석발현：1）사파량차전형여진 PGA 방대계수수고정선감소후증대，정명현적“요형”특정，“요형”부위위우단층위치，기 PGA 방대계수약위사파저부측점0.4～1.0，파정측점적 PGA 방대계수칙체도1.0～2.0배。유우 PGA 방대계수시재단층위치출현적명현괴점，종지질상표명료단층장지효응명현；（2）각점 NS ／UD 보비보편대우 EW／UD 보비。단렬구역탁월빈솔위저빈1Hz，소우기타측점적빈솔，대응보비최대치고체3.0～4.0，고우기타측점보비최대치。설명지표파렬처암토체송산파쇄，도치단층처적탁월빈솔교저，근장여진전파과래적고빈지진파피단층격단，지진가속도방대계수재해처발생료쇠감，장지효응현저。본연구유조우증강단층장지대사파동력향응영향적인식。
There are many landslides passed by faults.They are results from Wenchuan Ms 8.0 earthquake in 2008.Besides the movement of the seismogenic fault,its site effect can also influence the slope dynamic response and increase the slope instability.In this paper,the microtremors and seismic observations are performed along the front slope surface in Mianzhu Jiulong town.It uses the spectral ratio of horizontal to vertical components(H/V)of microtremor data and PGA amplification factors of acceleration records of two typical aftershocks,and obtains the spectral characteristic curves.By comparative analysis of the curves,it is found that:1 )with the growth of elevation,the values of PGA amplification factors decrease at first,and then increase,presenting a ‘concaveshape.The concave-shape curves appear at the monitoring point around the fault zone.The values of PGA amplification factors can just reach to 0.4 ~1.0,while the values of PGA amplification factors at the monitoring point around the upper slope can even get to be 1.0 ~2.0.As the turning points appear around the fault zone,it shows the site effects of the fault from the geological view.2)The NS /UD spectral ratio is generally greater than the EW/UD spectral ratio.The predominant frequency around the fault zone is near to the low frequency of 1Hz, smaller than any other monitoring point.It has the biggest spectral ratio of 3.0~4.0.It tells that the soil and rock of the surface rupture is loose and broken after the Wenchuan main shock.So the predominant frequency of the fault zone is low.The high frequencies of near-field aftershocks are filtered by the fault materials.Then the earthquake acceleration amplification coefficients are reduced as well.This study is helpful to enhance the understanding of the impact of the fault site effect on slope dynamic response.