SEISMOLOGY AND EGOLOGY ›› 2021, Vol. 43 ›› Issue (4): 984-998.DOI: 10.3969/j.issn.0253-4967.2021.04.016

• Research paper • Previous Articles     Next Articles

STUDY ON THE CHARACTERISTICS OF CO-SEISMIC GRAVITY CHANGE INDUCED BY MADUO MS7.4 EARTHQUAKE BASED ON OBSERVATIONS OF CONTINUOUS GRAVITY STATIONS

WEI Jin1,2,4)(), HAO Hong-tao1,2,4), HAN Yu-fei3), HU Min-zhang1,2,4), JIANG Ying1,2,4), LIU Zi-wei1,2,4)   

  1. 1) Institute of Seismology, CEA, Wuhan 430071, China
    2) Key Laboratory of Earthquake Geodesy, China Earthquake Administration, Wuhan 430071, China
    3) China Earthquake Networks Center, Beijing 100045, China
    4) Hubei Earthquake Agency, Wuhan 430071, China
  • Received:2021-06-15 Revised:2021-07-12 Online:2021-08-20 Published:2021-09-29

基于连续重力台观测的玛多MS7.4地震的同震重力变化特征

韦进1,2,4)(), 郝洪涛1,2,4), 韩宇飞3), 胡敏章1,2,4), 江颖1,2,4), 刘子维1,2,4)   

  1. 1)中国地震局地震研究所, 武汉 430071
    2)中国地震局地震大地测量重点实验室, 武汉 430071
    3)中国地震台网中心, 北京 100045
    4)湖北省地震局, 武汉 430071
  • 作者简介:韦进, 男, 1981年生, 2017年于武汉大学获大地测量学与测量工程专业博士学位, 副研究员, 主要从事连续重力观测数据的分析与应用研究, 电话: 15927365563, E-mail: pierce212@163.com
  • 基金资助:
    国家自然科学基金项目(41204058)

Abstract:

The Bayan Kara block is a secondary block in the Qinghai-Tibet Plateau interior with the strongest seismic activity occurring in the recent years. Unlike the 8 earthquakes above M7.0 occurring on the block boundary in the past 20 years, the Maduo MS7.4 earthquake occurred inside the block, thus providing a new research perspective for the composition of coseismic gravity change observations. At the same time, China Earthquake Administration set up 5 gPhone continuous gravity stations, which operated normally before and after the earthquake, about 800km away from the epicenter, near the northeast edge of the Qinghai Tibet Plateau and the adjacent areas. Among them, the Maqin gravity station is inside the block and the Songpan gravity station is on the block boundary. The location of this earthquake and the distribution characteristics of the gravity stations provide natural experimental sites and samples for studying the coseismic gravity change in the stations at different locations in and around the block. In order to check the dislocation theory based on surface deformation observation, accumulate coseismic gravity change data by strong earthquakes, and analyze the features of the coseismic gravity change by surface gravity observation from different perspectives, the gravity earth tide and barometric observation data measured by gPhone gravimeters and sampled at 1Hz in these 5 continuous gravity stations from May 10 to 25, 2021 are collected. In this paper, firstly, exponential and step function methods are used to extract the coseismic gravity change in these 5 gravity stations, so as to analyze whether the post-seismic gravity signals contain relaxation signal. The relaxation time observed by gravimeter is very short compared to the near-field results of Lushan MS7.0 earthquake, only about 11 minutes. And the step method result is more consistent with the model one. Comparing with the coseismic dislocation theory by Okubo and Sun model, it is found that the difference between the observation results of the two methods and the extreme value simulated by the two models is nearly 1×10-8m·s-2. Moreover, the observed and simulated results have a good consistency in terms of direction. However, there is about an order of magnitude difference between the observation and simulation in the gravity station position. By discussing the calculation accuracy of barometric admittance, mean tidal factor and co-seismic gravity change of 7-days data before and after the earthquake at the 5 stations, analyzing the relationship between the coseismic gravity change and vertical displacement in the same site of GNSS and gravity station at Maqin and Songpan, comparing the observations and simulations of the coseismic gravity changes in the two gravity stations(Maqin and Songpan)located at the block boundary and inside the block induced by the Jiuzhaigou MS7.0 and Maduo MS7.4 earthquake which occurred also on the block boundary and inside the block, and calculating the coseismic gravity change at Zhongdian station by the Maduo MS7.4 after removing the effect of Yangbi MS6.4 earthquake, it is considered that, these gPhone gravimeters analyzed in the paper can capture more than 0.5×10-8m·s-2 coseismic gravity change, and the Maqin station, which is about 175km away from the epicenter, observed about [(2.9±0.70)~(4.0±0.70)]×10-8m·s-2 coseismic gravity change generated by Maduo MS7.4 earthquake. Based on the daily solution of GNSS vertical displacement, the co-seismic vertical deformation at Maqin and Songpan stations is all about-(4±5)mm. Taking the average gravity gradient value, -320×10-8m·s-2/m, the displacement-induced gravity change by Maduo MS7.4 earthquake is calculated, which is(1.2±1.5)×10-8m·s-2. It is proved that part of the contribution of the co-seismic positive gravity variation at Maqin and Songpan stations comes from the variation of vertical deformation in this area. By eliminating the co-seismic effect from the Yangbi MS6.4, the co-seismic gravity change induced by Maduo MS7.4 earthquake in Zhongdian station is about(1.09±0.76)×10-8m·s-2. Compared with the observed and simulated co-seismic gravity change induced by Jiuzhaigou MS7.0 earthquake, the co-seismic gravity change of about(9.1±0.22)×10-8m·s-2 by Maduo MS7.4 earthquake recorded at Songpan station should include the effect of other factors. This may be related to the seismic and tectonic background, as Songpan station is just at the east boundary of Bayan Kara block. The coseismic gravity change in Linzhi station is negative, which is consistent with the simulation results of dislocation theory. Based on the observation results of this paper, it is considered that the Maduo MS7.4 earthquake can produce about(0.5~4)×10-8m·s-2 co-seismic gravity change in the far field range of 175~800km. The coseismic gravity variation signal observed by the gravity station is not only related to crustal deformation and epicentral distance, but also to the seismotectonic background of the block where the gravity station locates. The results can provide a reference for determining the coseismic gravity change caused by medium strong earthquakes in the future.

Key words: the Maduo MS7.4 earthquake, gPhone gravimeters, co-seismic gravity change, dislocation model

摘要:

同震重力变化可为位错模型的检验和约束提供新数据。 文中利用指数函数和阶跃函数法分析了玛多MS7.4地震震中距≤800km的5个重力台的同震重力信号。 结果显示: 观测和位错模型模拟结果的方向一致性好, 只是量级存在差异。 通过对同震重力变化精度的讨论, 同震重力变化和GNSS垂直位移的比较, 九寨沟MS7.0、 玛多MS7.4同震重力变化空间分布的分析, 以及漾濞MS6.4地震对同震重力变化影响的改正, 分析认为: 震中距为175km的玛沁台记录到(2.9~4.0)×10-8m·s-2 的同震重力变化; 震中距为763km的中甸台在改正了漾濞地震的影响后记录到1.09×10-8m·s-2 的同震重力变化; 松潘台记录的9.1×10-8m·s-2 的重力变化信号中应包含其他因素的影响; 林芝台的负变化规律和位错模型模拟结果方向一致。 综合文中的观测结果认为, 玛多MS7.4地震能够在175~800km的远场范围内产生约(0.5~4.0)×10-8m·s-2 的同震重力变化信号。 该结果可为未来中强地震远场产生的同震重力变化量级的判定提供参考。

关键词: 玛多MS7.4地震, gPhone重力仪, 同震重力变化, 位错模型

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