康定Ms6.3和Ms5.8级地震下 摩岗岭震动监测数据研究

为研究康定M_s6.3和M_s5.8级(M_s为面波震级)2次地震动的响应规律,在大渡河摩岗岭段两岸斜坡不同高程处掘进平硐并安置了强震监测仪。监测数据揭示1^#监测点记录的水平向和竖直向PGA(地表峰值加速度)最大,M_s6.3级水平向达到了16.5～22.2 cm/s²,竖直向也达到了8.9 cm/s²;M_s5.8级水平向为9.9～11.8 cm/s²,竖直向为4.1 cm/s²。以2^#监测点记录的2次地震加速度PGA值为参考,1^#监测点水平向和竖直向PGA放大系数最大,M_s6.3级水平向和竖直向放大系数分别达到5.4,4.2,而震级较小的M_s5.8分别为3.7,2.2。傅里叶谱分析可得各监测点记录的2次地震卓越频率相差不大。由各监测点加速度反应谱可得同次地震中海拔最高的1^#监测点水平向和竖直向反应谱幅值最大;对比同一监测点不同震级加速度反应谱,较大震级的M_s6.3级各个方向幅值比M_s5.8级大。研究表明斜坡不同高程部位对地震波具有选择放大作用,高程越大,这种放大效应越明显。

Analysis of Seismic Monitoring Data at Mogangling Slope During the Kangding Ms 6.3 and Ms 5.8 Earthquakes

In order to analyze the dynamic seismic response and topographic amplification effect of Kangding M_s6.3 and M_s5.8 earthquakes, we excavated adits at different altitudes and placed monitoring instruments on both sides of the slope at Mogangling segment of Dadu River. The monitoring data reveals that 1) the peak ground accelerations (PGA) in both horizontal and vertical directions at 1^# monitoring site are the biggest. In M_s6.3 earthquake, the PGA in horizontal and vertical direction is respectively 16.5-22.2 cm/s² and 8.9 cm/s², and in M_s5.8 earthquake the horizontal and vertical PGA is 9.9-11.8 cm/s² and 4.1 cm/s², respectively; 2) with the horizontal and vertical PGA at 2^# monitoring site as reference, the horizontal and vertical PGA amplification factors of 1^# monitoring site are the biggest, reaching 5.4 and 4.2 respectively in M_s6.3 earthquake and 3.7 and 2.2 respectively in M_s5.8 earthquake; 3) difference of predominant period of each monitoring site is not big in the same period frequency from Fourier spectrum in both earthquakes; 4) the acceleration response spectrum at each monitoring site shows that the horizontal and vertical amplitudes of 1^# monitoring site (which is in the highest altitude) are the biggest. For the same site, horizontal and vertical amplitudes of M_s6.3 earthquake are both larger than those of M_s5.8 earthquake. Studies suggest that under strong earthquake, seismic wave is amplified selectively in different parts of slope at different elevations, and topographic amplification effect of ground motion is bigger at higher altitude.