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<p>We used the single backscattering technique to compute Coda Q (Q<sub>C</sub>) and the geometrical spreading factor, gamma (γ), using the Coda Normalization approach for the active Kachchh region. The waveform data used in this study is from seismic stations operated by the Institute of Seismological Research, Gandhinagar, India, in the Kachchh region, located in the western part of the Deccan Volcanic Province. A total of 2869 seismograms from 548 local earthquakes with M<sub>w</sub> 3.0–5.3 and depths 1–42&#xa0;km, located within 200&#xa0;km of seismic stations with a signal-to-noise ratio ≥ 3, were analyzed for ‘Q<sub>C</sub>’ and ‘γ’ estimations. ‘Q<sub>C</sub>’ and ‘γ’ has been estimated at five central frequencies (1.5, 3, 6, 12 &amp; 20&#xa0;Hz) using 20&#xa0;s, 30&#xa0;s, 40&#xa0;s, and 50&#xa0;s window lengths for vertical, N-S, and E-W components. The obtained ‘Q<sub>C</sub>’ values show that the attenuation is strongly frequency-dependent, and points towards a heterogeneous medium. The ‘γ’ have been determined for two scenarios i.e. with and without attenuation (Q) correction. The average geometrical spreading factors with attenuation (Q) correction are 0.88, 1.12, 1.45, 1.39, 1.25, for central frequencies 1.5, 3, 6, 12 &amp; 20&#xa0;Hz respectively, whereas these factors are 1.36, 1.65, 2.02, 2.01, 1.88, in case of without attenuation (Q) correction. The main goal of this study is to demonstrate that the Earth’s crust is highly heterogeneous, making it inappropriate to assume that ‘γ’ is constant across all the regions. Regional variations in ‘γ’ values can be attributed to underlying geological conditions, which can influence the rate at which seismic waves attenuate with distance. In areas with complex and dynamic geology, such as the Kachchh region, region-specific ‘γ’ values must be used for accurate ground motion predictions and seismic hazard assessments.</p>

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A Study on Geometrical Spreading and Coda Wave Attenuation for the Tectonically Active Kachchh Region of Gujarat

  • 期刊论文

  • 发表日期：

    2026年1月22日

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  • Indu Bala,
  • Santosh Kumar,
  • Manisha Sandhu,
  • Sumer Chopra,
  • Dinesh Kumar

摘要

We used the single backscattering technique to compute Coda Q (QC) and the geometrical spreading factor, gamma (γ), using the Coda Normalization approach for the active Kachchh region. The waveform data used in this study is from seismic stations operated by the Institute of Seismological Research, Gandhinagar, India, in the Kachchh region, located in the western part of the Deccan Volcanic Province. A total of 2869 seismograms from 548 local earthquakes with Mw 3.0–5.3 and depths 1–42 km, located within 200 km of seismic stations with a signal-to-noise ratio ≥ 3, were analyzed for ‘QC’ and ‘γ’ estimations. ‘QC’ and ‘γ’ has been estimated at five central frequencies (1.5, 3, 6, 12 & 20 Hz) using 20 s, 30 s, 40 s, and 50 s window lengths for vertical, N-S, and E-W components. The obtained ‘QC’ values show that the attenuation is strongly frequency-dependent, and points towards a heterogeneous medium. The ‘γ’ have been determined for two scenarios i.e. with and without attenuation (Q) correction. The average geometrical spreading factors with attenuation (Q) correction are 0.88, 1.12, 1.45, 1.39, 1.25, for central frequencies 1.5, 3, 6, 12 & 20 Hz respectively, whereas these factors are 1.36, 1.65, 2.02, 2.01, 1.88, in case of without attenuation (Q) correction. The main goal of this study is to demonstrate that the Earth’s crust is highly heterogeneous, making it inappropriate to assume that ‘γ’ is constant across all the regions. Regional variations in ‘γ’ values can be attributed to underlying geological conditions, which can influence the rate at which seismic waves attenuate with distance. In areas with complex and dynamic geology, such as the Kachchh region, region-specific ‘γ’ values must be used for accurate ground motion predictions and seismic hazard assessments.