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<p>Large shallow slips play a key role in generating long-period ground motions near faults during inland crustal earthquakes with surface ruptures. In this study, we investigated the source characteristics of the shallow zone (≤ ~ 3&#xa0;km depth), interpreted as a weak layer with low S-wave velocities (≤ ~ 3&#xa0;km/s), to improve the recipe for broadband ground-motion simulations in Japan. We compiled source inversion results and long-period motion generation area (LMGA) models for six earthquakes (Mw ≥  ~ 6.5) and examined slip and source time functions in the shallow zone. The results indicate that the average slip in the shallow zone is approximately 1.2 times the overall average slip in the rupture area. The LMGA, corresponding to large-slip areas in the shallow zone, exhibits a slip of ~ 1.7 times the overall average slip and a slip duration of ~ 2–8&#xa0;s, suggesting that these regions are key in generating large long-period ground motion. Analysis of the geomorphological fault displacement data shows that the average fault displacement is approximately equal to the overall average slip, and the maximum fault displacement is approximately 2.5 times the overall average slip, indicating a quantitative proportional relationship between the geological and seismological parameters. These findings highlight the general characteristics of shallow-zone slip that are critical for reproducing large long-period ground motions in the near-fault region.</p> Graphical Abstract <p></p>

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Characterization of slip on fault in shallow zone above seismogenic zone for inland crustal earthquakes with surface ruptures

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年7月14日

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  • Ken Miyakoshi,
  • Yujia Guo,
  • Kazuhiro Somei,
  • Susumu Kurahashi,
  • Yasuhiro Matsumoto,
  • Naoto Inoue,
  • Takashi Kumamoto,
  • Katsuhiro Kamae,
  • Kojiro Irikura

摘要

Large shallow slips play a key role in generating long-period ground motions near faults during inland crustal earthquakes with surface ruptures. In this study, we investigated the source characteristics of the shallow zone (≤ ~ 3 km depth), interpreted as a weak layer with low S-wave velocities (≤ ~ 3 km/s), to improve the recipe for broadband ground-motion simulations in Japan. We compiled source inversion results and long-period motion generation area (LMGA) models for six earthquakes (Mw ≥  ~ 6.5) and examined slip and source time functions in the shallow zone. The results indicate that the average slip in the shallow zone is approximately 1.2 times the overall average slip in the rupture area. The LMGA, corresponding to large-slip areas in the shallow zone, exhibits a slip of ~ 1.7 times the overall average slip and a slip duration of ~ 2–8 s, suggesting that these regions are key in generating large long-period ground motion. Analysis of the geomorphological fault displacement data shows that the average fault displacement is approximately equal to the overall average slip, and the maximum fault displacement is approximately 2.5 times the overall average slip, indicating a quantitative proportional relationship between the geological and seismological parameters. These findings highlight the general characteristics of shallow-zone slip that are critical for reproducing large long-period ground motions in the near-fault region.

Graphical Abstract