关键词: 谱比值, 近断层, 地面运动, 集集地震, 场地条件

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