STUDY ON SPATIAL CORRELATION OF GROUND-MOTION: A CASE STUDY OF NAPA EARTHQUAKE

doi:10.3969/j.issn.0253-4967.2020.05.012

Abstract

Abstract: The probability of joint exceedance of ground motion intensities at multiple sites during the same earthquake needs to be quantified in aggregated seismic hazard analysis or loss assessment of spatially distributed infrastructure systems. The spatial correlation of ground motion at multiple sites cannot be considered in conventional specific-site seismic hazard analysis method. In this paper, the spatial correlation of ground motion is preliminarily studied using 344 sets of strong earthquake records from the M_W6.0 Napa earthquake, California, US on August 24, 2014. The results of finite fault inversion for Napa earthquake(Dreger et al., 2015)is used as the surface projection of fault rupture. The ground motion attenuation relationship of Boore in NGA-West2 in the Pacific Seismic Engineering Research Center, which is referred to as BSSA14 in this paper, is selected in this research. The local site amplification effect of ground motion is obtained by using the correlation between topographic slope and $V^{30}_{S}$(average shear wave velocity of rock and soil layer from surface to 30 meters underground)to obtain the site amplification coefficient of amplitude and frequency. The ground motion parameters actually observed by the station are converted to the reference surface of bedrock by using the site amplification coefficient, and the fault projection distance between each station and the surface projection of fault rupture is calculated. Comparison of strong ground motion recordings of the Napa earthquake with BSSA14 in the Next Generation Attenuation(NGA)-West2 Ground-Motion Models, indicates that the ground motion of the high frequency components of the Napa earthquake was underestimated in the attenuation relationship of BSSA14. And the peak ground acceleration residuals are mostly negative. The residuals of acceleration response spectrum for the 3-second period are basically distributed around the 0 value. The spatial correlation functions of the geometric mean for the peak ground acceleration(PGA), the peak ground velocity(PGV)and spectral acceleration at three specific periods(0.3s, 1.0s and 3.0s)of the two horizontal components are derived using the method of semivariogram function. 2km and 1km of the distance between stations is used in this paper respectively, which can guarantee the reliability of data calculation statistics. However, we found that the decrease of the distance between stations did not significantly improve the statistical results of the spatial correlation of strong ground motion in the observed data of Napa earthquake. The corresponding continuous spatial correlation function is fitted with exponential model and compared with the past studies of ground-motion correlation, which has been widely researched in the past. The analysis results show that the ground motion parameters are spatially correlated, and these spatial correlations approximate exponential decay as the distance increases. Secondly, the spatial correlation of ground motion increases with the increase of response spectrum period. It may be because the similarity is reduced by the scattering of waves during propagation, and that this reduction is greater for high-frequency waves. The short￣wavelength waves tend to be more affected or changed by small-scale heterogeneities in the process of propagation, so the spatial correlation of high-frequency seismic waves is smaller than that of long-period seismic waves. Finally, there is a regional characteristic in the spatial correlation of seismic ground motion. The spatial correlation of peak ground acceleration is weaker in southern California than in Japan and Taiwan. Results of this research in this paper can provide theoretical basis and reference for aggregated seismic hazard analysis or loss assessment. And uncertainty will be reduced in ShakeMap considering the spatial correlation of ground motion.

Key words: Napa earthquake, the ground-motion, spatial correlation, semivariogram

摘要： 在区域地震危险性分析或者损失评估中, 需要量化同一次地震中的多场点地震动强度被联合超越的概率。常规的特定场点地震危险性分析方法并不能处理场点间地震动的空间相关性问题。文中利用收集到的2014年8月24日美国加州纳帕 M_W6.0地震的344组强震记录, 初步研究了地震动在空间上的相关性。利用半变异函数方法计算获得了峰值加速度(PGA)、峰值速度(PGV)及3个特定周期(0.3s、 1.0s和3.0s)反应谱谱值的空间相关性函数, 通过指数模型拟合得到了其对应的连续的空间相关性函数, 并与先前的研究结果进行了比较。研究结果表明, 地震动参数存在空间相关性, 且随着距离的增大呈指数衰减; 地震动的空间相关性随着反应谱周期的增大而增大; 同时, 地震动的空间相关性存在区域性的特征, 峰值加速度的空间相关性在南加州地区比在日本和中国台湾地区更弱(衰减更快)。文中所得结论可为区域地震危险性分析、损失评估以及减小震后快速产出震动图(ShakeMap)的不确定性等提供理论依据和参考。

关键词: 纳帕地震, 地震动, 空间相关性, 半变异函数

CLC Number:

P315.9

CHEN Kun, YU Yan-xiang, GAO Meng-tan, KANG Chuan-chuan. STUDY ON SPATIAL CORRELATION OF GROUND-MOTION: A CASE STUDY OF NAPA EARTHQUAKE[J]. SEISMOLOGY AND GEOLOGY, 2020, 42(5): 1218-1228.

陈鲲, 俞言祥, 高孟潭, 亢川川. 地震动的空间相关性——以纳帕地震为例[J]. 地震地质, 2020, 42(5): 1218-1228.

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