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<p>The Tehran basin (Iran) is located in the central Alborz seismic zone, a region with very high seismicity due to the existence of numerous large active faults. Composed of Plio-Quaternary alluvium, the city of Tehran faces significant ground motion amplification (up to 7–8) over a wide frequency range from about 0.4&#xa0;Hz to 3&#xa0;Hz. This amplification is likely attributed to the thick alluvial deposits and the presence of strong lateral discontinuities that lead to multidimensional site effects. To better understand and predict the effects of the geometry and mechanical properties on surface ground motion in Tehran, we developed the first 3D shear-wave velocity model of the Tehran basin. This model was constructed by integrating geological, geophysical, and seismological datasets collected across the city. The dataset includes 197 near-surface seismic data points and geological logs. The geophysical data comprise 33 ambient noise array recordings, 13 active-source surface wave profiles, and 575 single-station ambient noise measurements. Geological stratigraphy, lithological properties, and time-averaged shear-wave velocity (Vs) over the first 30&#xa0;m depth (Vs30) were used to constrain the ground model parameterization in terms of the number of layers and Vs range in the near surface. Rayleigh and Love wave dispersion curves, Rayleigh wave ellipticity, and fundamental resonance frequency were then jointly inverted to derive one-dimensional (1D) shear-wave velocity profiles in sediments and seismic bedrock depths at array sites. Inversion results allowed us to develop an empirical relationship between the fundamental resonance frequency and seismic bedrock depth. A three-dimensional (3D) model of the basin was then constructed by extrapolating the bedrock depths across the area using fundamental resonance frequencies derived from horizontal-to-vertical (H/V) spectral ratio measurements. The final model reveals significant variation in seismic bedrock depth, ranging from approximately 90&#xa0;m to 900&#xa0;m, with pronounced lateral variability from the northeast to the southwest of the basin.</p>

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3D shear-wave velocity model of the Tehran (Iran) sedimentary basin by means of geological and geophysical data

  • 期刊论文

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  • 发表日期：

    2025年10月31日

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  • Saeed Soltani,
  • Ebrahim Haghshenas,
  • Bertrand Guillier,
  • Cécile Cornou

摘要

The Tehran basin (Iran) is located in the central Alborz seismic zone, a region with very high seismicity due to the existence of numerous large active faults. Composed of Plio-Quaternary alluvium, the city of Tehran faces significant ground motion amplification (up to 7–8) over a wide frequency range from about 0.4 Hz to 3 Hz. This amplification is likely attributed to the thick alluvial deposits and the presence of strong lateral discontinuities that lead to multidimensional site effects. To better understand and predict the effects of the geometry and mechanical properties on surface ground motion in Tehran, we developed the first 3D shear-wave velocity model of the Tehran basin. This model was constructed by integrating geological, geophysical, and seismological datasets collected across the city. The dataset includes 197 near-surface seismic data points and geological logs. The geophysical data comprise 33 ambient noise array recordings, 13 active-source surface wave profiles, and 575 single-station ambient noise measurements. Geological stratigraphy, lithological properties, and time-averaged shear-wave velocity (Vs) over the first 30 m depth (Vs30) were used to constrain the ground model parameterization in terms of the number of layers and Vs range in the near surface. Rayleigh and Love wave dispersion curves, Rayleigh wave ellipticity, and fundamental resonance frequency were then jointly inverted to derive one-dimensional (1D) shear-wave velocity profiles in sediments and seismic bedrock depths at array sites. Inversion results allowed us to develop an empirical relationship between the fundamental resonance frequency and seismic bedrock depth. A three-dimensional (3D) model of the basin was then constructed by extrapolating the bedrock depths across the area using fundamental resonance frequencies derived from horizontal-to-vertical (H/V) spectral ratio measurements. The final model reveals significant variation in seismic bedrock depth, ranging from approximately 90 m to 900 m, with pronounced lateral variability from the northeast to the southwest of the basin.