The influence of local site effects on seismic ground motions is an important issue in seismic hazard assessment and earthquake resistant design. Determining site effects in densely populated cities built on basins ca...The influence of local site effects on seismic ground motions is an important issue in seismic hazard assessment and earthquake resistant design. Determining site effects in densely populated cities built on basins can help to reduce the earthquake hazard. Site effects of Luoyang basin are estimated by the horizontal-to-vertical spectral ratio(HVSR) method using ambient noise records from a short-period dense array. The sites in Luoyang basin are sorted into three types according to the pattern of the HVSR curves. There are cases with a single clear peak, two clear peaks, and an unclear low frequency peak or multiple peaks, which correspond to there being one large impedance contrast interface, two large interfaces, and a moderate one beneath the sites, respectively. The site effects characterized by fundamental frequency from HVSR curves are affected by underlying sedimentary layers and depth of sedimentary basement. According to our results, the existence of thick sediment layer obviously lowers the fundamental frequency to the period range from 2 to 4 s in the downtown area of Luoyang city. The ground motion will amplify when through the sites and the buildings with height of 20–50 floors can resonate at the similar frequency domain. Site effects estimation using HVSR method from a short-period dense array is an effective technique in areas of moderate seismic risk where strong motion recordings are lacking, such as the Luoyang basin.展开更多
Determining the shallow structure of a sediment basin is important when evaluating potential seismic hazards given that such basins can significantly amplify seismic energy. The Luoyang basin is located in the western...Determining the shallow structure of a sediment basin is important when evaluating potential seismic hazards given that such basins can significantly amplify seismic energy. The Luoyang basin is located in the western He’nan uplift and is a Meso-Cenozoic depression basin. To characterize the shallow structure of the basin, we develop a model of the shallow high-resolution three-dimensional(3D)shear-wave velocity structure of the basin by applying ambient noise tomography to a dense array of 107 portable digital seismometers deployed over the basin. More than 1,400 Rayleigh-wave dispersion curves for periods in the range 0.5–5 s are extracted. The 3D variations of shear-wave velocity in the shallow crust are inverted using a direct surface-wave tomographic method with period-dependent ray tracing, with all the surface-wave group-velocity dispersion data being inverted simultaneously. The results show that in the shallow crust of the study area, the velocity distribution corresponds to surface geology and geological features. The Luoyang basin exhibits a low shear-wave velocity feature that is consistent with the distribution of sediment in the region,while the Xiongershan and Songshan uplifts exhibit higher shear-wave velocity structures. The results provide a shallow high-resolution 3D velocity model that can be used as a basis for simulation of strong ground motion and evaluation of potential seismic hazards.展开更多
地球化学指标在古气候研究中多用于黄土、湖泊等沉积物的分析,河流沉积物由于沉积水动力变化大,对其化学元素及其古气候指示意义的研究较少。文中对洛阳盆地4~3.8 ka BP龙山晚期古洪水(SQ)剖面地球化学指标的古气候指示意义进行了探讨...地球化学指标在古气候研究中多用于黄土、湖泊等沉积物的分析,河流沉积物由于沉积水动力变化大,对其化学元素及其古气候指示意义的研究较少。文中对洛阳盆地4~3.8 ka BP龙山晚期古洪水(SQ)剖面地球化学指标的古气候指示意义进行了探讨。分析显示,古洪水剖面的化学元素含量与中值粒径相关性显著。在排除物源、沉积再旋回和成岩钾交代作用对于化学元素的影响后,根据各化学元素与中值粒径的相关系数进行分组,并在同组内按照元素迁移强弱建立化学元素参数指标,其结果与CIA粒度效应校正结果具有一致性,均在距今4000年前后的古洪水层呈低值,指示相对干凉的气候。结合该剖面孢粉的分析结果,认为洛阳盆地温凉的气候条件是距今4000年前后古洪水事件发生的重要环境背景。虽然河流沉积过程的复杂性导致本研究具有一定的局限性,但是通过相关系数分组建立比值参数的方法,为探讨河流沉积物化学元素指标的古气候指示意义提供了新的思路。展开更多
对洛阳盆地平原区典型剖面的物质组成、测年数据和考古遗址空间分布特点的综合分析显示,该地区全新世地貌环境经历了伊、洛河一、二级阶地形成、阶地面接受洪积冲积物质和风尘物质不断加积、伊、洛河夹河滩地不断扩大的演变过程.二级阶...对洛阳盆地平原区典型剖面的物质组成、测年数据和考古遗址空间分布特点的综合分析显示,该地区全新世地貌环境经历了伊、洛河一、二级阶地形成、阶地面接受洪积冲积物质和风尘物质不断加积、伊、洛河夹河滩地不断扩大的演变过程.二级阶地形成于全新世初期,一级阶地形成于约3.1 ka BP,阶地形成的原因以气候变化为主,因此两级阶地为气候阶地;夹河滩地自晚全新世开始,因伊、洛河汇流点东移而不断扩大;引起滩地扩大的根本原因是人类活动的不断加强.展开更多
基金funded by the National Key R&D Program of China(No.2017YFC1500202)supported by the National Natural Science Foundation of China(No.41604048)China Earthquake Science Experiment(No.2016CESE0103)
文摘The influence of local site effects on seismic ground motions is an important issue in seismic hazard assessment and earthquake resistant design. Determining site effects in densely populated cities built on basins can help to reduce the earthquake hazard. Site effects of Luoyang basin are estimated by the horizontal-to-vertical spectral ratio(HVSR) method using ambient noise records from a short-period dense array. The sites in Luoyang basin are sorted into three types according to the pattern of the HVSR curves. There are cases with a single clear peak, two clear peaks, and an unclear low frequency peak or multiple peaks, which correspond to there being one large impedance contrast interface, two large interfaces, and a moderate one beneath the sites, respectively. The site effects characterized by fundamental frequency from HVSR curves are affected by underlying sedimentary layers and depth of sedimentary basement. According to our results, the existence of thick sediment layer obviously lowers the fundamental frequency to the period range from 2 to 4 s in the downtown area of Luoyang city. The ground motion will amplify when through the sites and the buildings with height of 20–50 floors can resonate at the similar frequency domain. Site effects estimation using HVSR method from a short-period dense array is an effective technique in areas of moderate seismic risk where strong motion recordings are lacking, such as the Luoyang basin.
基金supported by the China Spark Program(No.XH17055Y)the National Natural Science Foundation of China(No.41574084)
文摘Determining the shallow structure of a sediment basin is important when evaluating potential seismic hazards given that such basins can significantly amplify seismic energy. The Luoyang basin is located in the western He’nan uplift and is a Meso-Cenozoic depression basin. To characterize the shallow structure of the basin, we develop a model of the shallow high-resolution three-dimensional(3D)shear-wave velocity structure of the basin by applying ambient noise tomography to a dense array of 107 portable digital seismometers deployed over the basin. More than 1,400 Rayleigh-wave dispersion curves for periods in the range 0.5–5 s are extracted. The 3D variations of shear-wave velocity in the shallow crust are inverted using a direct surface-wave tomographic method with period-dependent ray tracing, with all the surface-wave group-velocity dispersion data being inverted simultaneously. The results show that in the shallow crust of the study area, the velocity distribution corresponds to surface geology and geological features. The Luoyang basin exhibits a low shear-wave velocity feature that is consistent with the distribution of sediment in the region,while the Xiongershan and Songshan uplifts exhibit higher shear-wave velocity structures. The results provide a shallow high-resolution 3D velocity model that can be used as a basis for simulation of strong ground motion and evaluation of potential seismic hazards.
文摘地球化学指标在古气候研究中多用于黄土、湖泊等沉积物的分析,河流沉积物由于沉积水动力变化大,对其化学元素及其古气候指示意义的研究较少。文中对洛阳盆地4~3.8 ka BP龙山晚期古洪水(SQ)剖面地球化学指标的古气候指示意义进行了探讨。分析显示,古洪水剖面的化学元素含量与中值粒径相关性显著。在排除物源、沉积再旋回和成岩钾交代作用对于化学元素的影响后,根据各化学元素与中值粒径的相关系数进行分组,并在同组内按照元素迁移强弱建立化学元素参数指标,其结果与CIA粒度效应校正结果具有一致性,均在距今4000年前后的古洪水层呈低值,指示相对干凉的气候。结合该剖面孢粉的分析结果,认为洛阳盆地温凉的气候条件是距今4000年前后古洪水事件发生的重要环境背景。虽然河流沉积过程的复杂性导致本研究具有一定的局限性,但是通过相关系数分组建立比值参数的方法,为探讨河流沉积物化学元素指标的古气候指示意义提供了新的思路。
文摘对洛阳盆地平原区典型剖面的物质组成、测年数据和考古遗址空间分布特点的综合分析显示,该地区全新世地貌环境经历了伊、洛河一、二级阶地形成、阶地面接受洪积冲积物质和风尘物质不断加积、伊、洛河夹河滩地不断扩大的演变过程.二级阶地形成于全新世初期,一级阶地形成于约3.1 ka BP,阶地形成的原因以气候变化为主,因此两级阶地为气候阶地;夹河滩地自晚全新世开始,因伊、洛河汇流点东移而不断扩大;引起滩地扩大的根本原因是人类活动的不断加强.
