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<p>On January 23, 2024, an <i>M</i><sub>s</sub> 7.1 earthquake struck Wushi County, Aksu region, Xinjiang, with its seismogenic structure identified as the NE-striking sinistral compressional Maidan Fault. To gain deeper insights into the seismogenic mechanism and precursory characteristics of this event, this study systematically investigates the spatiotemporal evolution of the gravity field, crustal apparent density changes, and time-series responses at specific points in the epicentral area. The analysis is grounded in the “field-source interaction” theoretical framework and utilizes high-precision mobile gravity observation data from Southern Xinjiang, covering the period from March 2020 to January 2024. The results reveal several key findings. Firstly, the spatiotemporal evolution of the gravity field shows a significant correlation with the earthquake triggering mechanism. During the seismogenic phase, the regional gravity field exhibited a characteristic four-quadrant distribution pattern, with the epicenter located near the center and the high-gradient zone. Immediately preceding the earthquake, the gravity field in the source area underwent a reversal from negative to positive, reflecting shear stress concentration caused by the migration of deep materials, which aligns with the Coulomb failure criterion. Secondly, multi-temporal apparent density inversion elucidates the deep response of tectonic activity. Equivalent source inversion results indicate that the apparent density changes in the epicentral crust ranged from −1.0 to +3.0 kg/m<sup>3</sup>, showing a significant correlation with the surface gravity anomaly intensity (±80 µGal). This confirms the efficacy of the equivalent source method in extracting weak tectonic signals from complex background fields and clarifies that crustal mass migration and stress accumulation are crucial physical mechanisms driving the earthquake. Finally, time-series analysis of point values uncovers the evolutionary pattern of gravity precursors. Data from five measurement points near the epicenter show a slow upward trend in gravity before the earthquake, which transitioned to an accelerated rise during the immediate foreshock period, with a maximum change of 103 µGal. This indicates that the directional migration of materials, such as deep high-pressure fluids, led to a sharp increase in density in the source area, ultimately triggering the instability of the fault. Through multi-dimensional gravity analysis, this study systematically reveals the coupled evolution characteristics of the gravity, density, and stress fields during the preparation of the Wushi earthquake. It enhances the understanding of the mechanisms behind strong earthquakes and validates the significant value of time-varying gravity fields in identifying seismic precursors and delineating hazardous zones.</p>

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Research on Gravity and Apparent Density Changes in the Focal Area before and after the Wushi Ms7.1 Earthquake

  • 期刊论文

  • 发表日期：

    2026年1月14日

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  • Lei Zhao,
  • Yassen Abdutair,
  • Dai-Qin Liu,
  • YuShan Ailixiati,
  • Li Chen,
  • Jie Li,
  • Kai Han,
  • Xiang-Kui Kong

摘要

On January 23, 2024, an Ms 7.1 earthquake struck Wushi County, Aksu region, Xinjiang, with its seismogenic structure identified as the NE-striking sinistral compressional Maidan Fault. To gain deeper insights into the seismogenic mechanism and precursory characteristics of this event, this study systematically investigates the spatiotemporal evolution of the gravity field, crustal apparent density changes, and time-series responses at specific points in the epicentral area. The analysis is grounded in the “field-source interaction” theoretical framework and utilizes high-precision mobile gravity observation data from Southern Xinjiang, covering the period from March 2020 to January 2024. The results reveal several key findings. Firstly, the spatiotemporal evolution of the gravity field shows a significant correlation with the earthquake triggering mechanism. During the seismogenic phase, the regional gravity field exhibited a characteristic four-quadrant distribution pattern, with the epicenter located near the center and the high-gradient zone. Immediately preceding the earthquake, the gravity field in the source area underwent a reversal from negative to positive, reflecting shear stress concentration caused by the migration of deep materials, which aligns with the Coulomb failure criterion. Secondly, multi-temporal apparent density inversion elucidates the deep response of tectonic activity. Equivalent source inversion results indicate that the apparent density changes in the epicentral crust ranged from −1.0 to +3.0 kg/m3, showing a significant correlation with the surface gravity anomaly intensity (±80 µGal). This confirms the efficacy of the equivalent source method in extracting weak tectonic signals from complex background fields and clarifies that crustal mass migration and stress accumulation are crucial physical mechanisms driving the earthquake. Finally, time-series analysis of point values uncovers the evolutionary pattern of gravity precursors. Data from five measurement points near the epicenter show a slow upward trend in gravity before the earthquake, which transitioned to an accelerated rise during the immediate foreshock period, with a maximum change of 103 µGal. This indicates that the directional migration of materials, such as deep high-pressure fluids, led to a sharp increase in density in the source area, ultimately triggering the instability of the fault. Through multi-dimensional gravity analysis, this study systematically reveals the coupled evolution characteristics of the gravity, density, and stress fields during the preparation of the Wushi earthquake. It enhances the understanding of the mechanisms behind strong earthquakes and validates the significant value of time-varying gravity fields in identifying seismic precursors and delineating hazardous zones.