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<p>This study investigates the ongoing crustal deformation and seismic interactions in the northwestern Himalayan foreland, using the 2019 Mirpur earthquake sequence (<i>Mw</i> 5.8). The aftershock sequence follows the Omori–Utsu decay law, with a decay constant (<i>p</i>-value) of 0.9 observed over a 200-day period. However, seismic activity did not return to background levels after this time, indicating sustained stress perturbations in the region. Following the mainshock, the average seismicity rate in the Mirpur–Kharian region increased by a factor of three. This sustained seismicity suggests permanent activation of subsurface geological structures, likely driven by poroelastic effects associated with coseismic stress redistribution. A decrease in the <i>b</i>-value from 0.69 ± 0.06 to 0.54 ± 0.04 was observed in a declustered aftershock catalog. This reduction likely reflects an increase in differential stress or the reactivation of locked asperities. In December 2024, a moderate earthquake (<i>Mw</i> 5.0) occurred near Kharian, approximately 30&#xa0;km northeast of the 2019 epicenter, within a zone where Coulomb stress had increased by ~ 0.04&#xa0;bar. This spatial correlation suggests a causal link through static stress transfer and poroelastic relaxation. Temporal stress evolution was examined using seismicity rate inversion. Results show a stress step of ~ 1.6&#xa0;bar produced by the mainshock, accompanied by a tenfold increase in the background stress rate, from 0.031&#xa0;bar/year to 0.3&#xa0;bar/year. These findings reveal that postseismic deformation is partitioned between two regimes: aseismic slip along a mid-crustal viscous décollement beneath the Salt Range, and continued brittle failure within the overlying seismogenic layer. Together, these processes highlight the complex rheological coupling at the deformation front in this tectonically active region.</p>

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Crustal stress redistribution and aftershock patterns in the Northwestern Himalaya following the 2019 Mirpur earthquake

  • 期刊论文

  • 发表日期：

    2025年10月4日

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  • Mohammad Tahir,
  • Muhammad Yousaf Khan,
  • Seema Tahir,
  • Talat Iqbal

摘要

This study investigates the ongoing crustal deformation and seismic interactions in the northwestern Himalayan foreland, using the 2019 Mirpur earthquake sequence (Mw 5.8). The aftershock sequence follows the Omori–Utsu decay law, with a decay constant (p-value) of 0.9 observed over a 200-day period. However, seismic activity did not return to background levels after this time, indicating sustained stress perturbations in the region. Following the mainshock, the average seismicity rate in the Mirpur–Kharian region increased by a factor of three. This sustained seismicity suggests permanent activation of subsurface geological structures, likely driven by poroelastic effects associated with coseismic stress redistribution. A decrease in the b-value from 0.69 ± 0.06 to 0.54 ± 0.04 was observed in a declustered aftershock catalog. This reduction likely reflects an increase in differential stress or the reactivation of locked asperities. In December 2024, a moderate earthquake (Mw 5.0) occurred near Kharian, approximately 30 km northeast of the 2019 epicenter, within a zone where Coulomb stress had increased by ~ 0.04 bar. This spatial correlation suggests a causal link through static stress transfer and poroelastic relaxation. Temporal stress evolution was examined using seismicity rate inversion. Results show a stress step of ~ 1.6 bar produced by the mainshock, accompanied by a tenfold increase in the background stress rate, from 0.031 bar/year to 0.3 bar/year. These findings reveal that postseismic deformation is partitioned between two regimes: aseismic slip along a mid-crustal viscous décollement beneath the Salt Range, and continued brittle failure within the overlying seismogenic layer. Together, these processes highlight the complex rheological coupling at the deformation front in this tectonically active region.