Abstract: The vertical to horizontal response spectra ratio (V/H) for 68 near-fault records (R_rup<20km) and 48 eastern coast records (40<R_rup<70)from the 1999 Chi-Chi earthquake has been studied in this article. The concerned records are divided into groups according to stations' position(handing-wall or footwall),Slte、ondition and distance to the fault. This study focuses on the relationship between V/H and fault orientation and rupture direction,distance to fault,and local site condition. Some of the results attained in this paper are(onsistent with previous(onclusions,while others are somewhat different. The difference seems to reflect the specific(haracteristics of near fault ground motion of the studied event. The results in this article show that:1)the directions of fault slip and rupture propagation have(onsiderable effect on the V/H within 31im to the fault rupture. Mainly at short and medium periods,V/H of paralleling rupture direction is greater than that perpendicular to the rupture. In footwall and distance range of 3～20km,Slte、ondition has slight effect on V/H;2) for the Chi-Chi earthquake,the V/H in long-period range(>3s) is、ommonly larger than 2/3,the usually estimated value in references,with a noticeable peals,which means the long period component of vertical movement in this、ase is larger than that of other earthquakes;3)for recordings at footwall side,the V/H in short periods(<0.2s)do not obviously decrease as rupture distance increases. Comparing to stations having larger rupture distances(>40km),V/H of near fault stations are、ommonly larger in the、oncerned periods in engineering、ircle;4)the influence of site (onditions on the spectral ratio seems insignificant in near fault area. For the east stations with larger distance,the V/H in long period range at hard soil site is longer than that at soft soil site.

Key words: spectral ratio, near fault, ground motion, Chi-Chi Earthquake, site condition

摘要： 选取了1999年9月21日台湾集集7.6级地震主震中68组断层距在20km以内的近断层台站记录和46组断层距在40～70km的东部台站记录,按台站的上下盘位置、场地条件和断层距分组,对其竖向和水平加速度反应谱比值V/H进行了统计分析。研究表明:1)断层的滑动方向和断层破裂的传播方向对断层距在3km以内的台站上的地面运动谱比值V/H有一定影响,且主要体现在中短周期范围内,例如平行断层方向的谱比值要比垂直断层方向的谱比值大。在下盘断层距3～20km的范围内,场地条件对V/H基本没有影响。2)在集集地震中长周期(>3s)部分的谱比值通常>32,且有一个较高的峰值,表明其竖向运动加速度中的长周期分量大于其它地震。3)对于下盘的台站,地面运动在短周期(<0.2s)段的谱比值不随断层距的增加而减少。与中远(>40km)距离的台站相比较,近断层台站的V/H在工程界关心的周期范围内普遍较大。4)场地条件对谱比值V/H的影响在近断层处不显著。在远离断层的东部台站上,硬土场地谱比值V/H在长周期段大于软土场地。

关键词: 谱比值, 近断层, 地面运动, 集集地震, 场地条件