Active-source surface wave exploration is advantageous because it has high imaging accuracy,is not affected by high-speed layers,and has a low cost;thus,it has unique advantages for investigating shallow surface struc...Active-source surface wave exploration is advantageous because it has high imaging accuracy,is not affected by high-speed layers,and has a low cost;thus,it has unique advantages for investigating shallow surface structures.For the development and utilization of urban underground space,two parameters in the shallow surface are important,namely,the shear wave velocity(V_(S))and the predominant period of the site,which determine the elevation and aseismic grade of the building design.The traditional method is mainly to obtain the two above-mentioned parameters through testing and measuring drilling samples.However,this method is extremely expensive and time consuming.Therefore,in this research,we used the multichannel surface wave acquisition method to extract the fundamental dispersion curve of single-shot data by using the phase shift method and obtain the V_(S) characteristics in the uppermost 40 m by inversion.We arrived at the following two conclusions based on the V_(S) profile.First,the study area can be roughly divided into five layers,among which the layers 0−8 m,14−20 m,and 20−30 m are low-velocity layers,corresponding to miscellaneous fill,a water-bearing sand layer,and a sand layer;therefore,the V_(S) is relatively low.In contrast,the layers at 8−14 m and 30−40 m are high-velocity layers that are mainly composed of clay,with a relatively better compactness and relatively high V_(S) values.In addition,a low-speed anomaly appears abruptly in the high-speed area at 20−40 m.This anomaly,when combined with geological data,suggests that it is an ancient river channel.Second,from the V_(S) value,the V_(Se)(equivalent shear wave velocity)was calculated.The construction site soil was categorized as class III,with good conditions for engineering geology.In addition,we calculated the predominant period of the site to be 0.56-0.77 s based on the V_(S).Therefore,in the overall structural design of the foundation engineering,the natural vibration period of the structure should be strictly controlled to avoid the predominant period of the site.展开更多
在城市中应用微动H/V谱比方法面对大量且复杂的人文噪声干扰,需要对噪声强度较大的微动数据进行去噪处理或信号分析。本文针对现有方法难以处理干扰较大的微动数据以及信号提取过程繁琐的问题,提出基于XGBoost(extreme gradient boosti...在城市中应用微动H/V谱比方法面对大量且复杂的人文噪声干扰,需要对噪声强度较大的微动数据进行去噪处理或信号分析。本文针对现有方法难以处理干扰较大的微动数据以及信号提取过程繁琐的问题,提出基于XGBoost(extreme gradient boosting)的多重加权谱比降噪方法。首先对采集的微动数据进行幅值和频率分析,建立幅值加权谱比、频率加权谱比和多重加权谱比;然后根据建立的多重加权谱比,通过XGBoost方法获得降噪后的谱比曲线。将本文方法与传统STA/LTA(short time average/long time average)方法进行实际高噪声数据对比分析,结果表明相比于STA/LTA方法,本文方法对高噪声数据提取效果更好。展开更多
基金This study was supported by the National Natural Science Foundation of China(grant nos.42074115,41574094)the National Key R&D Program of China(grant no.2017YFC0601301)+1 种基金the Geological Survey Project of the China Geological Survey(grant no.DD20189132)the Key Laboratory of Deep-Earth Dynamics,Ministry of Natural Resources(grant no.J1901-3).
文摘Active-source surface wave exploration is advantageous because it has high imaging accuracy,is not affected by high-speed layers,and has a low cost;thus,it has unique advantages for investigating shallow surface structures.For the development and utilization of urban underground space,two parameters in the shallow surface are important,namely,the shear wave velocity(V_(S))and the predominant period of the site,which determine the elevation and aseismic grade of the building design.The traditional method is mainly to obtain the two above-mentioned parameters through testing and measuring drilling samples.However,this method is extremely expensive and time consuming.Therefore,in this research,we used the multichannel surface wave acquisition method to extract the fundamental dispersion curve of single-shot data by using the phase shift method and obtain the V_(S) characteristics in the uppermost 40 m by inversion.We arrived at the following two conclusions based on the V_(S) profile.First,the study area can be roughly divided into five layers,among which the layers 0−8 m,14−20 m,and 20−30 m are low-velocity layers,corresponding to miscellaneous fill,a water-bearing sand layer,and a sand layer;therefore,the V_(S) is relatively low.In contrast,the layers at 8−14 m and 30−40 m are high-velocity layers that are mainly composed of clay,with a relatively better compactness and relatively high V_(S) values.In addition,a low-speed anomaly appears abruptly in the high-speed area at 20−40 m.This anomaly,when combined with geological data,suggests that it is an ancient river channel.Second,from the V_(S) value,the V_(Se)(equivalent shear wave velocity)was calculated.The construction site soil was categorized as class III,with good conditions for engineering geology.In addition,we calculated the predominant period of the site to be 0.56-0.77 s based on the V_(S).Therefore,in the overall structural design of the foundation engineering,the natural vibration period of the structure should be strictly controlled to avoid the predominant period of the site.
文摘在城市中应用微动H/V谱比方法面对大量且复杂的人文噪声干扰,需要对噪声强度较大的微动数据进行去噪处理或信号分析。本文针对现有方法难以处理干扰较大的微动数据以及信号提取过程繁琐的问题,提出基于XGBoost(extreme gradient boosting)的多重加权谱比降噪方法。首先对采集的微动数据进行幅值和频率分析,建立幅值加权谱比、频率加权谱比和多重加权谱比;然后根据建立的多重加权谱比,通过XGBoost方法获得降噪后的谱比曲线。将本文方法与传统STA/LTA(short time average/long time average)方法进行实际高噪声数据对比分析,结果表明相比于STA/LTA方法,本文方法对高噪声数据提取效果更好。
