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<p>The Main Himalayan Thrust (MHT) is the principal seismogenic structure beneath Nepal, yet the extent to which catalog-scale seismicity reflects along-strike segmentation remains uncertain. We analyze an International Seismological Centre (ISC) earthquake catalog, queried through FDSN services, covering 1990–2025 within 80–89°E and 26–31°N, retaining events with reported depths of 0–50&#xa0;km and preferred magnitudes of M ≥ 3.0. The filtered catalog contains 3,864 events. Frequency-magnitude diagnostics indicate Mc ≈ 3.55 from the maximum-curvature method and Mc ≈ 3.70 from the 95% goodness-of-fit criterion; we therefore use M ≥ 3.7 for completeness-limited robustness tests. Normalized along-strike density curves are calculated using a 0.5° moving-window baseline and are tested against alternative window widths and Gaussian smoothing parameters for the full catalog, the M ≥ 3.7 catalog, and a Gardner-Knopoff aftershock-reduced M ≥ 3.7 catalog. Two low-density sectors near 82.6°E and 84.1–84.2°E persist after completeness thresholding, declustering, and exclusion of the 2015 Gorkha sequence window. A third low-density sector near 86.7°E weakens and shifts eastward after declustering, indicating sensitivity to sequence clustering. These results support first-order along-strike heterogeneity in Nepal Himalayan seismicity, but they do not directly resolve the geometry of the MHT. The inferred sectors are therefore interpreted as empirical candidate transitions that can be independently evaluated using relocated hypocenters, focal mechanisms, velocity models, and geodetic coupling constraints.</p>

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Along-strike seismicity heterogeneity and catalog-scale low-density sectors in the Nepal Himalaya

  • 期刊论文

  • 发表日期：

    2026年7月24日

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  • Suchita Shrestha,
  • Tae-Seob Kang,
  • Hyun Jae Yoo

摘要

The Main Himalayan Thrust (MHT) is the principal seismogenic structure beneath Nepal, yet the extent to which catalog-scale seismicity reflects along-strike segmentation remains uncertain. We analyze an International Seismological Centre (ISC) earthquake catalog, queried through FDSN services, covering 1990–2025 within 80–89°E and 26–31°N, retaining events with reported depths of 0–50 km and preferred magnitudes of M ≥ 3.0. The filtered catalog contains 3,864 events. Frequency-magnitude diagnostics indicate Mc ≈ 3.55 from the maximum-curvature method and Mc ≈ 3.70 from the 95% goodness-of-fit criterion; we therefore use M ≥ 3.7 for completeness-limited robustness tests. Normalized along-strike density curves are calculated using a 0.5° moving-window baseline and are tested against alternative window widths and Gaussian smoothing parameters for the full catalog, the M ≥ 3.7 catalog, and a Gardner-Knopoff aftershock-reduced M ≥ 3.7 catalog. Two low-density sectors near 82.6°E and 84.1–84.2°E persist after completeness thresholding, declustering, and exclusion of the 2015 Gorkha sequence window. A third low-density sector near 86.7°E weakens and shifts eastward after declustering, indicating sensitivity to sequence clustering. These results support first-order along-strike heterogeneity in Nepal Himalayan seismicity, but they do not directly resolve the geometry of the MHT. The inferred sectors are therefore interpreted as empirical candidate transitions that can be independently evaluated using relocated hypocenters, focal mechanisms, velocity models, and geodetic coupling constraints.