SEISMOLOGY AND GEOLOGY ›› 2024, Vol. 46 ›› Issue (5): 1151-1171.DOI: 10.3969/j.issn.0253-4967.2024.05.009

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THE CHARACTERISTICS AND MECHANISM OF GRAVITY AND MAGNETIC FIELD CHANGES BEFORE AND AFTER THE 2014 HUOSHAN MS4.3 EARTHQUAKE

LIANG Xiao1,2,3)(), CHU Fei1,2,3),*(), XU Ru-gang1,2,3), SUN Hong-bo1,2), XIAO Wei-peng1,2), WANG Jun1)   

  1. 1) Anhui Earthquake Agency, Hefei 230031, China
    2) Mengcheng National Geophysical Observation and Research Station, Mengcheng 233500, China
    3) Anhui Provincial Joint Construction Key Laboratory of Subsurface Exploration and Earthquake Hazard Risk Prevention(in prep.), Hefei 230031, China
  • Received:2023-10-16 Revised:2024-07-30 Online:2024-10-20 Published:2024-11-22

2014年霍山MS4.3地震前后重磁场变化特征及机理分析

梁霄1,2,3)(), 储飞1,2,3),*(), 徐如刚1,2,3), 孙鸿博1,2), 肖伟鹏1,2), 王俊1)   

  1. 1) 安徽省地震局, 合肥 230031
    2) 安徽蒙城地球物理国家野外科学观测研究站, 蒙城 233500
    3) 安徽省地下结构探测与震灾风险防范联合共建重点实验室(筹), 合肥 230031
  • 通讯作者: 储飞, 男, 1988年生, 高级工程师, 主要从事流动重力、 地磁及跨断层水准的数据处理及分析工作, E-mail: 115781226@qq.com
  • 作者简介:

    梁霄, 男, 1991年生, 2017年于长江大学获得地球探测与信息技术专业硕士学位, 工程师, 主要从事流动重力、 流动地磁、 跨断层水准观测与数据处理及分析工作, E-mail:

  • 基金资助:
    中国地震局地震监测、 预报、 科研三结合课题(3JH-202402026); 中国地震局地震监测、 预报、 科研三结合课题(3JH-202401029); 武汉引力与固体潮国家野外科学观测研究站开放基金(WHYWZ202209); 中国地震局震情跟踪专项任务(2024010414); 中国地震局地震科技星火计划项目(XH22002YA)

Abstract:

Before the Huoshan earthquake, significant anomalies were detected in both the gravity and lithospheric magnetic fields. To comprehensively analyze the variations in these fields and their underlying mechanisms before and after the Huoshan earthquake, we used mobile gravity data from 2010 to 2015 and mobile geomagnetic data from 2013 to 2014 in Anhui Province and surrounding regions. Our analysis focused on gravity field changes from two perspectives: (1)the spatial and temporal variations in the gravity field and(2)the time series of gravity point values across the seismogenic fault(Tudiling-Luoerling fault). Additionally, we corrected for diurnal variations and long-term trends in the geomagnetic field, allowing us to track changes in the three components of the lithospheric magnetic field—total intensity, magnetic inclination, and declination—before and after the earthquake. Using wavelet multi-scale decomposition, we calculated and analyzed wavelet details at different decomposition scales for the gravity and magnetic field variations in the first half year before the Huoshan earthquake. Finally, in conjunction with underground fluid data, we examined the seismogenic background and explored the underlying reasons for the precursory anomalies observed in the geophysical fields.

The research yielded the following conclusions: Prior to the Huoshan earthquake, an anomalous high-gradient zone in both the gravity field and the total strength of the lithospheric magnetic field was observed, extending approximately 100km. Notably, the total magnetic field strength in the Huoshan area significantly decreased before the earthquake. The gravity field exhibited a small initial decline, evolving into a high-gradient anomaly zone parallel to the seismogenic fault, which culminated in the earthquake occurring near the zero contour of gravity change. The alignment of the zero lines of gravity and magnetic field changes with the strike of the seismogenic fault suggests that tectonic faults play a critical role in controlling crustal deformation and underground fluid migration. When combined with a comprehensive analysis of the regional stress field, underground fluid dynamics, and variations in the gravity and magnetic fields, this information can be instrumental in identifying and assessing seismic risk zones.

The Huoshan region is highly susceptible to seismic activity due to the influence of the Bayan Har block in the Qinghai-Tibet region, which induces stress field fluctuations in the area. The MS7.0 Lushan earthquake in Sichuan, on April 20, 2013, significantly impacted the regional stress field, resulting in the opening of the “Huoshan Seismic Window.” In the six months preceding the Huoshan earthquake, there was an increase in crustal movement, as well as a marked rise in minor seismic activity. These factors accelerated the adjustment of the regional stress state and the migration of underground fluids, leading to expanded variations in regional gravity and magnetic fields. The Huoshan MS4.3 earthquake exhibited distinct precursory anomalies. The wavelet multi-scale decomposition of gravity and magnetic field changes suggests that the source of the Huoshan earthquake likely originated in the middle to lower crust. The deformation and material migration in the upper crust appeared to be influenced by processes in the middle and lower crust, with energy accumulation in the upper crust triggering the opening of the “Huoshan Seismic Window” and the subsequent earthquake. Additionally, the extreme point of the wavelet details in the lithospheric magnetic field change was located near the zero line of the wavelet details in the gravity field and the fault development area.

This study concludes that regional stress fluctuations, crustal deformation, and underground fluid migration are controlled by fracture structures. The migration of underground fluids and other materials results in notable changes in the gravity and magnetic fields, particularly in areas with concentrated fault activity, underscoring the potential for predicting earthquakes using geophysical precursor signals such as gravity and lithospheric magnetic field changes.

Key words: Earthquake, Gravity field, Geomagnetic field, Wavelet analysis, Underground fluid

摘要:

文中利用安徽省及周边地区2010—2015年流动重力和2013—2014年流动地磁资料, 系统分析了霍山地震前后重力和岩石圈磁场三分量随时间的变化特征, 利用小波分析法提取震前重磁场变化不同分解尺度的小波细节, 结合地下流体资料探讨了霍山地震的发震背景和震前地球物理场前兆异常明显的原因。霍山地震前, 重力场与岩石圈磁场总强都形成了异常变化的高梯度带, 异常范围约为100km, 梯度带的走向与发震断裂一致, 地壳形变与地下流体运移明显受到构造断裂的控制。岩石圈磁场总强在霍山地区出现了较大幅度下降, 重力场经历了“区域整体微小负值变化—形成重力异常高梯度带—在重力变化零等值线附近发震”的演化过程。震前半年“霍山窗”开窗, 小地震活动显著增强, 区域地壳运动水平显著上升, 加速了区域应力状态的调整与地下流体的运移, 导致了重磁场震前的显著变化; 小波分析结果显示, 磁场变化的极值点靠近重力场变化的零值线及断裂发育区域, 表明重力场与岩石圈磁场的变化具有一定的相关性, 进一步揭示了基于重力与岩石圈磁场变化等地球物理前兆信息预报地震的可能, 结合区域应力场、 地下流体、 重力场与岩石圈磁场变化的综合分析, 更有利于震前地震危险区的划定及危险性研判。

关键词: 地震, 重力场, 岩石圈磁场, 小波多尺度分解, 地下流体