Active faults pose a great threat to urban security.As the largest NW-trend active fault in Beijing area,the Nankou-Sunhe fault plays an important role in earthquake disaster and city construction.In this study,we col...Active faults pose a great threat to urban security.As the largest NW-trend active fault in Beijing area,the Nankou-Sunhe fault plays an important role in earthquake disaster and city construction.In this study,we collect continuous ambient noise data recorded by 43 temporary short-period seismograph between September 21th to October 12th 2019 to investigate the near-surface structure beneath the Nankou-Sunhe fault by using ambient noise tomography(ANT)and horizontal-to-vertical spectral ratio(HVSR)method.From ambient noise processing,fundamental-mode Rayleigh wave signals are clearly observed in the frequency band of 0.4-2.5 Hz.Then direct surface-wave inversion algorithm is applied to calculate the 3D shear-wave velocity model.Our results show that there is a sharp velocity contrast across the Nankou-Sunhe fault,with low velocities down to about 2 km on the hanging wall and high velocity on the footwall of the fault.According to the geological investigation,the low velocities are related to thicker sediments and Jurassic volcanic rock below which are the cap rock of the hydrothermal system.From the HVSR analysis,the HVSR curves of the sites near the fault shows double-peak,one less than 1 Hz and the other centered 7 Hz.After converting frequency to depth by the empirical equation,the results show that the thickness of sediments is thinned from southwest to northeast,which generally agrees well to field survey.Our results provide high-resolution near-surface structure for future study on disaster risk reduction and urban planning.展开更多
The faults and fractures are known as two of the most important parameters in earthquake occurrence.During the construction in urban areas, faults and fractures may be covered in depth and thus are not visible at the ...The faults and fractures are known as two of the most important parameters in earthquake occurrence.During the construction in urban areas, faults and fractures may be covered in depth and thus are not visible at the ground surface. In this context, non-invasive geophysical prospecting methods(microtremor and geoelectrical methods) and borehole data were used to detect subsurface geological structures(hidden faults) in a suburb of Shiraz in Iran. The horizontal to vertical spectral ratio(HVSR) method was used to obtain the dynamic parameters(predominant frequency and resonance amplitude) of the soil, to detect hidden faults. The results show that the abrupt changes in the sediment thickness and predominant frequencies at a specific direction(NW-SE) can be related to the displacement of a nearly vertical fault with NW-SE trend. In addition, the electrical resistivity method using continuous resistivity profiling(CRP) and Schlumberger arrays was employed to detect a hidden fault and the results were compared with previous data. The obtained results of both arrays illustrate the presence of a nearly vertical fault with NW-SE trend in the region. Comparison of all results shows that the detected faults by both methods are consistent with each other. Therefore, it can be conclusive that combination of the two methods is a useful and reliable approach to study and detect hidden faults.展开更多
建筑物的共振频率是结构健康监测(Structural Health Monitoring,SHM)的重要指标。人们通常认为该指标受地震事件或环境变化影响最大,但很少有人讨论人类活动对它的影响。为了对福建省防灾减灾中心大楼进行结构健康监测,并分析人类活动...建筑物的共振频率是结构健康监测(Structural Health Monitoring,SHM)的重要指标。人们通常认为该指标受地震事件或环境变化影响最大,但很少有人讨论人类活动对它的影响。为了对福建省防灾减灾中心大楼进行结构健康监测,并分析人类活动对建筑物共振频率的影响,通过分析地震背景噪声数据,采用水平垂直谱比法(Horizontal to Vertical Spectral Ratio,HVSR),得出中心大楼地基的场地放大频带为1.5~3.5 Hz的多峰宽频带,大楼顶层的共振放大频带为以1.4 Hz左右为中心的单峰频带。大楼共振放大和场地效应处于同一频带,但放大程度是场地的近10倍。同时,顶层的HVSR谱幅值呈现出与人类活动有关的日变化、周变化特征,即春节、周末和夜间幅值小,工作日的白天幅值大。大楼的共振频率变化呈突变和渐变两个过程。其中,突变表现为:工作日白天,建筑物共振频率集中在1.36 Hz附近,其他时间集中在1.48 Hz附近,是被人类活动影响的体现;渐变表现为:在每天夜间、春节和大部分周末,中心大楼的共振频率不断上升,展现了建筑物共振频率恢复的动态过程。本研究的结果有助于建筑结构健康监测中考虑人类活动对共振频率的影响及共振频率的恢复,并为类似建筑物的健康监测提供参考。展开更多
近年来的工程实践表明,以速度频散特性为理论基础的传统瑞利面波法的实际应用存在场地限制的瓶颈问题.为克服该困难,本文从面波的基础理论着手,在前人建立的水平层状介质中瑞利面波速度频散方程的基础上,推导了水平层状介质中瑞利面波...近年来的工程实践表明,以速度频散特性为理论基础的传统瑞利面波法的实际应用存在场地限制的瓶颈问题.为克服该困难,本文从面波的基础理论着手,在前人建立的水平层状介质中瑞利面波速度频散方程的基础上,推导了水平层状介质中瑞利面波质点位移的解析解公式.以工程中常见的几种典型的水平层状地层模型为例,结合地脉动单点谱比法(HVSR,Horizontal to Vertical Spectral Ratio),对基阶瑞利面波的椭圆极化特征进行了数值模拟研究.研究结果表明:与瑞利面波的速度频散特性类似,其椭圆极化同样具有频散特性,且椭圆极化时的质点位移水平分量与垂直分量的频谱比与地层泊松比结构有关.瑞利面波的这种椭圆极化特性展示了利用单点瑞利面波的多分量评价地层泊松比结构的理论可行性.展开更多
基金supported by Beijing Natural Science Foundation(No.8212041)National Natural Science Foundation of China(Nos.41874063 and U1939203)Shanghai Sheshan National Geophysical Observatory(No.2020K02).
文摘Active faults pose a great threat to urban security.As the largest NW-trend active fault in Beijing area,the Nankou-Sunhe fault plays an important role in earthquake disaster and city construction.In this study,we collect continuous ambient noise data recorded by 43 temporary short-period seismograph between September 21th to October 12th 2019 to investigate the near-surface structure beneath the Nankou-Sunhe fault by using ambient noise tomography(ANT)and horizontal-to-vertical spectral ratio(HVSR)method.From ambient noise processing,fundamental-mode Rayleigh wave signals are clearly observed in the frequency band of 0.4-2.5 Hz.Then direct surface-wave inversion algorithm is applied to calculate the 3D shear-wave velocity model.Our results show that there is a sharp velocity contrast across the Nankou-Sunhe fault,with low velocities down to about 2 km on the hanging wall and high velocity on the footwall of the fault.According to the geological investigation,the low velocities are related to thicker sediments and Jurassic volcanic rock below which are the cap rock of the hydrothermal system.From the HVSR analysis,the HVSR curves of the sites near the fault shows double-peak,one less than 1 Hz and the other centered 7 Hz.After converting frequency to depth by the empirical equation,the results show that the thickness of sediments is thinned from southwest to northeast,which generally agrees well to field survey.Our results provide high-resolution near-surface structure for future study on disaster risk reduction and urban planning.
文摘基于2018年松原5.7级地震的强震动记录,结合在强震台站获取的地脉动数据,采用水平与竖向谱比(horizontal-to-vertical spectral ratio,HVSR)法和速度反应谱谱比(velocity response spectral ratio,VRSR)法,探究了强震台站场地的地震响应特征。结果表明:(1)地脉动水平与竖向谱比(horizontal-to-vertical spectral ratio of microtremors,MHVR)法、强震动水平与竖向谱比(horizontal-to-vertical spectral ratio of earthquake motions,EHVR)法以及VRSR都能较好地表征出场地地震响应峰值频段,达里巴、东三家子、风华以及宝甸等4个强震台站场地的(一阶)峰值频率范围分别为0.90~1.48 Hz,0.51~0.89 Hz,0.47~0.98 Hz,0.66~1.10 Hz;(2)同一场地条件下,MHVR,EHVR以及VRSR得出的场地放大系数差别较大,MHVR的放大系数最小,VRSR的放大系数整体较EHVR大,达里巴、东三家子、风华以及宝甸等4个强震台站场地与(一阶)峰值频率对应的放大系数范围分别为2.63~8.60,3.21~8.19,3.56~8.41以及4.14~7.96;(3)与MHVR相比,EHVR和VRSR都能较好地体现出地震动高频特征,且具有大致相同的变化趋势;(4)与EHVR相比,VRSR给出的低频信息更为丰富,但较为频繁的波动变化对峰值频率的快速识别具有一定程度的影响。该研究可为依托强震记录和地脉动数据开展场地地震响应分析提供参考,具有一定的工程应用价值。
基金supported by the Center of Excellence for Environmental Geohazards and the Research Council of Shiraz University
文摘The faults and fractures are known as two of the most important parameters in earthquake occurrence.During the construction in urban areas, faults and fractures may be covered in depth and thus are not visible at the ground surface. In this context, non-invasive geophysical prospecting methods(microtremor and geoelectrical methods) and borehole data were used to detect subsurface geological structures(hidden faults) in a suburb of Shiraz in Iran. The horizontal to vertical spectral ratio(HVSR) method was used to obtain the dynamic parameters(predominant frequency and resonance amplitude) of the soil, to detect hidden faults. The results show that the abrupt changes in the sediment thickness and predominant frequencies at a specific direction(NW-SE) can be related to the displacement of a nearly vertical fault with NW-SE trend. In addition, the electrical resistivity method using continuous resistivity profiling(CRP) and Schlumberger arrays was employed to detect a hidden fault and the results were compared with previous data. The obtained results of both arrays illustrate the presence of a nearly vertical fault with NW-SE trend in the region. Comparison of all results shows that the detected faults by both methods are consistent with each other. Therefore, it can be conclusive that combination of the two methods is a useful and reliable approach to study and detect hidden faults.
文摘近年来的工程实践表明,以速度频散特性为理论基础的传统瑞利面波法的实际应用存在场地限制的瓶颈问题.为克服该困难,本文从面波的基础理论着手,在前人建立的水平层状介质中瑞利面波速度频散方程的基础上,推导了水平层状介质中瑞利面波质点位移的解析解公式.以工程中常见的几种典型的水平层状地层模型为例,结合地脉动单点谱比法(HVSR,Horizontal to Vertical Spectral Ratio),对基阶瑞利面波的椭圆极化特征进行了数值模拟研究.研究结果表明:与瑞利面波的速度频散特性类似,其椭圆极化同样具有频散特性,且椭圆极化时的质点位移水平分量与垂直分量的频谱比与地层泊松比结构有关.瑞利面波的这种椭圆极化特性展示了利用单点瑞利面波的多分量评价地层泊松比结构的理论可行性.
