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<p>The Cambay Rift Basin of western India is an asymmetric rift formed during Late Cretaceous-Early Tertiary rifting and has been extensively studied for hydrocarbon exploration. It is bounded by ENE-WSW to E-W trending normal faults that define horst–graben geometries, and it remains tectonically active, as reflected in moderate seismicity. In this study, 52 microtremor measurements were carried out along two E–W profiles in the Patan and Mehsana regions to investigate shallow subsurface structure. Horizontal-to-Vertical Spectral Ratio (HVSR) analyses provided 1D shear-wave velocity and fundamental frequency estimates at each site. Predominant frequencies range from 0.11 to 5&#xa0;Hz in Patan and 0.12–1.5&#xa0;Hz in Mehsana, indicating strong lateral variations in sediment thickness. The 1D shear-wave velocity models identify 3–4 major stratigraphic layers, with velocities increasing with depth and maximum values of 1150–1500&#xa0;m/s occurring in the thick sedimentary zones. Bedrock is shallow near basin margins but deepens towards the central graben due to faulted blocks. Major stratigraphic layers, including the Cambay Shale, were mapped up to ~ 1800&#xa0;m depth, consistent with magnetotelluric and gravity studies. The derived V<sub>S30</sub> values from 1D velocity models lie between 285 and 480&#xa0;m/s. Overall, the study highlights the potential of microtremor surveys as a rapid and cost-effective tool for subsurface characterization in complex tectonic settings such as the Cambay Rift Basin. While the HVSR-based modelling provides robust first-order constraints on site resonance characteristics, the inferred subsurface models remain inherently non-unique and represent geologically plausible solutions constrained by the available ambient noise data.</p>

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Imaging shallow velocity structure and major stratigraphic layers using microtremor surveys: a case study from the northern Cambay Rift

  • 期刊论文

  • 发表日期：

    2026年7月15日

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  • Harsh Limbachiya,
  • Sumer Chopra

摘要

The Cambay Rift Basin of western India is an asymmetric rift formed during Late Cretaceous-Early Tertiary rifting and has been extensively studied for hydrocarbon exploration. It is bounded by ENE-WSW to E-W trending normal faults that define horst–graben geometries, and it remains tectonically active, as reflected in moderate seismicity. In this study, 52 microtremor measurements were carried out along two E–W profiles in the Patan and Mehsana regions to investigate shallow subsurface structure. Horizontal-to-Vertical Spectral Ratio (HVSR) analyses provided 1D shear-wave velocity and fundamental frequency estimates at each site. Predominant frequencies range from 0.11 to 5 Hz in Patan and 0.12–1.5 Hz in Mehsana, indicating strong lateral variations in sediment thickness. The 1D shear-wave velocity models identify 3–4 major stratigraphic layers, with velocities increasing with depth and maximum values of 1150–1500 m/s occurring in the thick sedimentary zones. Bedrock is shallow near basin margins but deepens towards the central graben due to faulted blocks. Major stratigraphic layers, including the Cambay Shale, were mapped up to ~ 1800 m depth, consistent with magnetotelluric and gravity studies. The derived VS30 values from 1D velocity models lie between 285 and 480 m/s. Overall, the study highlights the potential of microtremor surveys as a rapid and cost-effective tool for subsurface characterization in complex tectonic settings such as the Cambay Rift Basin. While the HVSR-based modelling provides robust first-order constraints on site resonance characteristics, the inferred subsurface models remain inherently non-unique and represent geologically plausible solutions constrained by the available ambient noise data.