Combination of passive and active methods towards site characterization of accelerometer stations in Greece

IF 1.1 4区 地球科学 Q3 GEOCHEMISTRY & GEOPHYSICS Near Surface Geophysics Pub Date : 2023-02-22 DOI:10.1002/nsg.12248
George Papadopoulos, Ilias Fikos, Antonio Garcia‐Jerez, Nikolaos Theodoulidis, George Vargemezis
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Abstract

Abstract The strong correlation between earthquake damage and the local geological conditions in an area has long been established, and site characterization studies are common practice for realistic estimation of seismic hazard and mitigation of the respective seismic risk. Estimation of the time‐averaged S‐waves velocity of the topmost 30 m ( V S30 ) is recognized as a basic proxy for site characterization and has been incorporated in several building codes. In our work, we examine the inversion of single‐station ambient noise horizontal to vertical spectral ratio (HVSR) curves to estimate the local one‐dimensional (1D) V S( Z ) structure. The inversion is performed based on the diffuse field assumption, which allows for the inversion of HVSR, including the contributions of both body and surface waves. Although ambient noise data acquisition is immensely cost‐effective, HVSR curve inversion is subject to the solution non‐uniqueness issue, offering ambiguous results. To provide a possible solution for this matter, additional near‐surface geophysical methods such as the multichannel analysis of surface waves and the electrical resistivity tomography (ERT) were applied to derive information on the shallow subsurface structure. The acquired 1D seismic velocity profile was implemented as initial model in the HVSR inversion to constrain the velocities of the upper meters. Additionally, the inferred stratigraphy from the ERT electrical profile was utilized to constrain the thicknesses of the layers. Tests were conducted with and without a priori information from complementary techniques to explore how the HVSR inversion procedure is facilitated. The proposed methodology was applied at the locations of six accelerometers in the city of Thessaloniki, northern Greece, under different geological conditions. The reliability of the inverted V S( Z ) models was checked by performing 1D numerical simulations of ambient noise waveforms generated by distributed sources and by direct comparison between synthetic ambient noise HVSR and single‐station earthquake HVSR curves.
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希腊加速度计站点特征的被动和主动结合方法
地震灾害与当地地质条件之间的强相关性早已确立,场地特征研究是现实估计地震危险性和减轻相应地震风险的常用方法。最上层30米的时间平均横波速度(vs30)的估计被认为是场地特征的基本代表,并已纳入几个建筑规范。在我们的工作中,我们研究了单站环境噪声水平与垂直频谱比(HVSR)曲线的反演,以估计局部一维(1D) V - S(Z)结构。反演是基于漫射场假设进行的,该假设允许反演HVSR,包括体波和面波的贡献。虽然环境噪声数据采集非常经济有效,但HVSR曲线反演受解非唯一性问题的影响,结果模糊不清。为了提供一个可能的解决方案,额外的近地表地球物理方法,如多通道表面波分析和电阻率层析成像(ERT),被应用于获得浅层地下结构的信息。将获取的一维地震速度剖面作为HVSR反演的初始模型,约束上层地层的速度。此外,利用ERT电剖面推断的地层学来约束层的厚度。在有和没有来自互补技术的先验信息的情况下进行了测试,以探索如何促进HVSR反演过程。所提出的方法在希腊北部城市塞萨洛尼基不同地质条件下的六个加速度计的位置进行了应用。通过对分布震源产生的环境噪声波形进行一维数值模拟,并直接比较合成环境噪声HVSR曲线和单站地震HVSR曲线,验证了倒V - S(Z)模型的可靠性。
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来源期刊
Near Surface Geophysics
Near Surface Geophysics 地学-地球化学与地球物理
CiteScore
3.60
自引率
12.50%
发文量
42
审稿时长
6-12 weeks
期刊介绍: Near Surface Geophysics is an international journal for the publication of research and development in geophysics applied to near surface. It places emphasis on geological, hydrogeological, geotechnical, environmental, engineering, mining, archaeological, agricultural and other applications of geophysics as well as physical soil and rock properties. Geophysical and geoscientific case histories with innovative use of geophysical techniques are welcome, which may include improvements on instrumentation, measurements, data acquisition and processing, modelling, inversion, interpretation, project management and multidisciplinary use. The papers should also be understandable to those who use geophysical data but are not necessarily geophysicists.
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