Random characteristics of ground motions during the 2012 Yiliang-Weining MS5.5 and MS5.6 earthquakes in Yunnan-Guizhou region
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摘要: 2012年9月7日我国西南云贵交界彝良-威宁地区连续发生两次MS5.5和MS5.6中强地震，其时间间隔短，震中位置接近，震级相差很小，为中强地震地震动的随机特性分析研究提供了难得的强震动数据. 本文从集系与样本函数两方面考虑，通过加速度时程的相关函数研究了地震动随机过程的相关特性. 结果表明： 两次地震集系的相关矩阵均为随机相关，互相关矩阵较自相关矩阵表现出更强的随机性；两次地震在同一个台站记录的加速度时程所构成的集系，其相关性较两次地震单独构成的集系好；样本函数的相关函数均呈现不规则震荡衰减的特点，且两个采样值间时滞越大，其样本函数相关性越小. 相比大震(如我国台湾地区的集集地震)，中强地震地震动记录的相关矩阵及分解后的自相关函数均表现出不同的特点. 由于这两次地震的地震动幅值相比大震较小，土层非线性影响较弱，故本文结果为认识地震动的随机特性提供了新的参考依据.Abstract: On 7 September 2012, two earthquakes took place consecutively at the boundary between Yiliang county in Yunnan Province and Weining county in Guizhou Province, southwestern China. They are characterized by a short time-interval, close epicentral position and small difference in the earthquake magnitude, which provides a number of valuable strong ground motion recordings for analyses and researches on random characteristics of ground motions. In the present paper, the correlative characteristics of seismic stochastic process through correlation functions of acceleration histories are studied from the aspect of the set systems and sample functions. The results show that, correlation matrices of set systems for ground motions during the two earthquakes are random. Comparison with autocorrelation matrices indicates that cross-correlation matrices show greater randomness. Set systems that are composed of acceleration histories for the two earthquakes with the same station are correlated better than those for individual earthquake. Correlation functions of sample functions both show irregular fluctuant attenuation characteristics; correlation of sample functions becomes poorer with time difference of the sampling values increasing. In comparison with great earthquake (such as the Chi-Chi earthquake), correlation matrices and autocorrelation functions after decomposition of the moderate ground motion recordings both exhibit different characteristics. Because both two earthquakes have smaller ground motion amplitudes and weaker soil nonlinear effect, so the results provide new references for understanding the random characteristics of ground motions.
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Keywords:
- Yiliang-Weining earthquake /
- correlation /
- set system /
- sample function /
- random characteristic
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图 1 记录到云贵彝良-威宁MS5.5和MS5.6地震的台站分布示意图
Figure 1. Schematic diagram of distribution of seismic stations for the Yiliang-Weining MS5.7 and MS5.6 earthquakes Circles represent the stations that recorded the MS5.7 earthquake，squares represent the stations that recorded the MS5.7 and MS5.6 earthquakes simultaneously,and the triangles represent the stations that recorded the MS5.6 earthquake only
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图 2 MS5.6地震23组加速度时程的自相关矩阵和互相关矩阵
Figure 2. Autocorrelation matrices and cross-correlation matrices of 23 acceleration time-histories for the MS5.6 earthquake
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图 3 53ZTJ台站在两次地震中的加速度时程互相关矩阵
Figure 3. Cross-correlation matrices of accele-ration time-histories of two earthquakes recorded by the station 53ZTJ
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图 4 第一组EW-EW分量间的相关性比较
Figure 4. Comparison of correlativity between EW and EW components for the first group
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图 5 MS5.6地震三分量样本函数的自相关函数和互相关函数．绿色线条为其平均值
Figure 5. Autocorrelation functions and cross-correlation functions of sample functions of the MS5.6 earthquake. Green thick curves denote the average value of correlation functions
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图 6 四级包络线(a)和幅值平稳化后的加速度时程(b)
Figure 6. The fourth-stage envelope (b) and acceleration time history after amplitude stabilization (b)
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图 7 MS5.6地震23组加速度时程的平均穿零率曲线
Figure 7. Average wear zero rate curves of 23 acceleration time histories for the MS5.6 earthquake
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图 8 MS5.6地震23组加速度时程EW分量(21—40 s)的一次自相关函数(a)和四次自相关函数(b). 图中绿色粗线为自相关函数的平均值
Figure 8. The first-order autocorrelation functions (a) and fourth-order autocorrelation functions (b) of EW component from 21 to 40 seconds of 23 acceleration time histories for the MS5.6 earthquake. Green thick lines are the average of the autocorrelation functions
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图 9 51MCL台站四次自相关函数及相应的确定性函数和随机函数
Figure 9. The fourth-order autocorrelation function (dark curve) of the station 51MCL and its corresponding deterministic function (red curve) and random function (blue curve)
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图 10 MS5.6 (a)和MS5.7 (b)地震地震动的自相关函数和互相关函数
Figure 10. Autocorrelation functions and cross-correlation functions for MS5.6 (a) and MS5.7 (b) earthquakes Black lines represent autocorrelation functions of EW, NS, UD component, respectively; green curves represent the cross-correlation function between EW and NS component, red curves represent the cross-correlation function between NS and UD component, blue curves represent the cross-correlation function between UD and EW component
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图 11 MS5.6(上)和MS5.7(下)地震动互相关函数的一次自相关函数(a)和多次自相关函数(b) 黑色曲线为EW分量与NS分量互相关函数的自相关函数，红色曲线为NS分量与UD分量 互相关函数的自相关函数，蓝色曲线为UD分量与EW分量互相关函数的自相关函数
Figure 11. The first-order autocorrelation functions (a) and multi-order autocorrelation functions (b) of cross-correlation functions of MS5.6 (upper) and MS5.7 (lower) earthquakes Black curves represent the autocorrelation function of cross-correlation function between EW and NS component， red curves represent the autocorrelation function of cross-correlation function between NS and UD component， blue curves represent the autocorrelation function of cross-correlation function between UD and EW component
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