SEISMOLOGY AND GEOLOGY

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P-wave velocity changes in hypocenter region of 2014 Jinggu Ms6.6 earthquake using Time-lapse tomography based on double-difference tomography

  

  • Received:2020-07-06 Revised:2020-11-25 Online:2020-02-20 Published:2021-09-26
  • Contact: Ying Cao

利用时移层析成像方法分析2014年云南景谷Ms6.6地震震源区的P波速度变化

曹颖1,钱佳威2,黄江培1,张国权1   

  1. 1. 云南省地震局
    2. 中国科技大学
  • 通讯作者: 曹颖
  • 基金资助:
    云南省地震局科技专项

Abstract: Of methods for measuring temporal changes in seismic-wave speeds in the Earth,seismic tomography is among those that offer the highest spatial resolution. In order to obtain the high spatial resolution P-wave velocity changes in the hypocenter region of the 2014 Jinggu Ms6.6 earthquake. We use the seismic data in the hypocenter region of the Jinggu earthquake recorded by the Yunnan Digital Seismic Network from January 1, 2008 to December 31, 2017, and We first used the double-difference tomography method to invert the high-resolution three-dimensional P-wave velocity structure in the hypocenter region of the Jinggu earthquake by combining absolute and relative arrival time. The inversion results show that the aftershock sequence is distributed at the junction of the P-wave high-speed anomaly area and the low-speed anomaly area. The faults that intersect the Lancangjiang Fault is in the low-velocity anomaly zone, which may be related to the fluid in the faults. Then we used the time-lapse tomography method based on double-difference tomography to obtain the spatial and temporal distribution of P-wave velocity changes between different time periods. In addition, combining the results with the existing geological and geophysical researc, the characteristics and mechanism of P-wave velocity changes are explored, our results indicate that (1) The maximum decrease in P-wave velocity at the shallow depth near the epicenter of the main earthquake was 0.2%, which occurred two months after the main earthquake and was mainly affected by rock damage. (2) There is an area of P-wave velocity rise at the depth of 5km to 15km. It is speculated that this area is a brittle-ductile transition zone, and is not affected by the occurrence of the main shock. After the occurrence of Ms5.8 and Ms5.9 aftershocks on December 6, the distribution direction of aftershocks changed significantly, the depth of the source deepened, the brittle-ductile transition zone was affected by these two earthquakes so that the P wave velocity decreased to 3.8%. (3) About three years after the Jinggu earthquake, the P-wave velocity increase above the pre-earthquake level. The healing process in the hypocenter region may also include the stress accumulation process before the Ms5.9 earthquake in Mojiang, Yunnan on September 8, 2018.

Key words: Jinggu earthquake, Time-lapse seismic tomography, Double-difference seismic tomography, P-wave velocity changes

摘要: 为了获得2014年景谷Ms6.6地震发生前后10年间震源区高空间分辨率的P波速度变化,本文联合2008年1月1日至2017年12月31日由云南区域数字地震台网所记录的景谷地震震源区的地震资料,首先采用双差层析成像方法联合绝对到时和相对到时反演了景谷地震震源区高分辨率的三维P波速度结构,反演结果表明景谷地震余震序列分布于P波高速异常区及低速异常区的交界处,与澜沧江断裂有所相交的断裂处于低速异常区,这可能与断层中的流体有关。然后采用基于双差层析成像的时移层析成像方法得到了不同时间段之间的P波速度变化的时空分布,并结合已有的地质与地球物理研究成果,对P波速度的变化特征及其机制进行了探究,得到几点认识:(1)景谷主震震中附近的浅层深度的P波速度下降最大降幅为0.2%,出现在景谷主震发生两个月后,主要受岩石破坏所影响。(2)5km至15km深度处整体存在P波速度上升条带区域,推测该区域为高强度、高阻介质的脆韧性转换带,不受主震发生的影响。在12月6日Ms5.8及Ms5.9余震发生后,余震分布方向发生了明显变化,震源深度加深,脆韧性转换带受其影响而P波速度下降至3.8%。(3)震后约3年,P波速度上升超过震前水平,可能震源区的愈合过程还包含了2018年9月8日云南墨江Ms5.9地震发生前的应力积累过程。

关键词: 景谷地震, 时移层析成像, 双差层析成像, P波速度变化