Preliminary Analysis of Long-period Ground Motion in Xingtai
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摘要: 沉积平原中存在地表低速沉积层是长周期地震动产生的关键因素，而长周期地震动会对长周期建筑物造成严重威胁和震害。本文基于邢台地震的历史地震震源模型和含地表沉积层的地壳速度模型，采用离散波数有限元法，对邢台地区进行了长周期地震动的计算分析。研究表明，邢台平原地区在大震中会产生长周期地震波，邢台地震中反应谱峰值区域位于宁晋南，与极震区基本重合。震中距小于55km区域内的周期1.5—4s的放大系数谱超过了抗震设计规范谱，反应谱放大系数值在周期2s附近达到峰值。因此，邢台地区因存在地表软弱沉积层，该区抗震设防可能对长周期地震动估计不足，建议应予以特别考虑。Abstract: The low velocity sediment on the plain is the main factor which generates the strong long-period waves. And the long-period ground motion may cause severe damage to high-rise buildings. We obtain crustal velocity structure including shallow part and historical earthquake source, and discrete wavenumber finite element method is used to calculate synthetic seismogram. Our results show that long-period ground motion will appear in strong earthquakes due to the existence of low velocity sediment in the Xingtai region. Then, the peak area we calculate and the meizoseismal area in the Xingtai earthquake appear to overlap. The amplification coefficient is larger than the seismic design code in 1.5-4s when epicentral distance is less than55 km, and amplification coefficient reaches peaks on 2s. The long-period part of the seismic design codes of Xingtai plain may exist shortage, more attention should be paid in the future.
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图 1 邢台地震震源机制及邢台地区断层分布
F1：新河断裂；F2：晋县断裂；F3：隆尧断裂；F4：衡水断裂；
F5：元氏断裂；F6：邯郸断裂；F7：明化镇断裂；F8：鸡泽断裂Figure 1. Focal mechanism of the Xingtai earthquake and fault distribution
图 2 实际速度模型模拟速度记录波形
Figure 2. Velocity waveforms simulated with actual velocity structure
图 3 Crust 2.0速度模型速度记录波形
Figure 3. Velocity waveforms simulated with Crust 2.0 velocity structure
图 6 加速度反应谱分布（单位：cm/s2）
Figure 6. Distribution of acceleration response spectrum (unit: cm/s2)
表 1 966年邢台宁晋东南7.2级地震震源参数
Table 1. Source parameter of the 1966 Xingtai MS 7.2 earthquake
参数 数值 断裂 新河断裂 地震矩M0 2.87×1027dyne·cm 应力降Δσ 32.3bar 断层长度 50km 断层宽度 17km 上升时间 1s 破裂速度 2km/s 震中经度 115.03°E 震中纬度 37.32°N 震源深度 9km 走向 NNE30° 滑动角 162° 倾角 45°NWW向正断层 
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表 2 邢台地区含地表浅部的速度结构模型
Table 2. Crustal velocity structure including shallow part in the Xingtai region
层数 深度/km 厚度/km vp/km·s-1 vs/km·s-1 ρ/g·cm-3 1 0.25 0.25 2.5 1.4 2.0 2 0.5 0.25 3.0 1.7 2.2 3 0.75 0.25 3.4 1.8 2.35 4 1 0.25 3.5 2.0 2.45 5 2 1 4.05 2.2 2.55 6 3 1 4.1 2.25 2.6 7 4 1 4.15 2.3 2.6 8 5 1 5.0 2.9 2.7 9 8 3 5.7 3.4 2.7 10 12 4 6.1 3.6 2.75 11 16 4 6.3 3.7 2.75 12 20 4 6.4 3.8 2.8 13 25 5 6.5 3.8 2.8 14 30 5 6.8 3.8 2.8 15 35 5 7.0 4.1 2.9 16 40 5 8.0 4.7 3.0
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