龙祠地震台毗邻的麦圪岭小山地形对背景噪声的影响

Impact study of Mai-Ge-Ling Hill Terrain Adjacent to Long-Ci Seismic Station on Background Noise

大规模流动地震台阵观测已经成为高分辨率深、浅部结构成像的重要手段和发展方向,台基条件和背景噪声是影响流动地震观测质量的关键因素.为了研究地形条件对背景噪声的影响,服务于降噪流动观测技术的发展要求,开展了龙祠地震台毗邻的麦圪岭小山地形对背景噪声的放大影响研究.通过地震观测和开放体系的时域显式波动有限元SH、P-SV波动数值模拟分析,结果表明,(1)不管是把白噪声信号当作SH型地震动,还是当作P-SV型地震动,山顶相对于山洞的传递函数,在频率16—18Hz之间,发现了由于山体地形导致的背景噪声的放大效应,该结果与背景噪声的观测结果相一致;(2)从山顶、山腰、山洞到山脚这4个观测点,数值模拟的震动响应最大值逐渐减小,揭示了地形放大效应,山顶相对于山脚的放大因子约为2.0;(3)场地土层对背景噪声的放大效应显著,甚至远超过地形效应的影响.

Large-scale flow observation of seismic array has become an important development direction of high-resolution deep and shallow structure imaging, while base station conditions and background noise are key factors that affect observation quality of flow seismic observation. To study the topographical conditions impacting on background noise, amplification impact study of Mai-Ge-Ling hill terrain adjacent to Long-Ci Seismic Station on background noise is carried out for meeting the development requirements of noise reduction technology of flow observation. By comparison of seismic observations and numerical simulation on SH and P-SV wave propagation of explicit finite element in time-domain, the results show that： （ 1 ） Consistent with the results of background noise observations, transfer function of the peak relative to the cave is prominent in the frequency between 16--18Hz, which reveals hill terrain causing the amplification of background noise, whether taking background noise signal as the SH-type ground motion, or taking it as the P-SV-type ground motion ; （2） From four observation points, which are hill peak, mountainside, cave and hill foot, the maximum of numerical simulation on seismic impulse response are decrease, which reflecting the topographic amplification effect. Relative to the hill foot, amplification factor of the hill peak is about 2. O; （ 3 ） Soil site amplification effect on background noise is significant, and even far more than the topographic effect.