地震地质 ›› 2023, Vol. 45 ›› Issue (5): 1074-1091.DOI: 10.3969/j.issn.0253-4967.2023.05.003

• 研究论文 • 上一篇    下一篇

InSAR数据约束的鲜水河断裂带北西段震间滑动速率及浅部蠕滑特征

陈毅(), 赵斌*(), 熊维, 王伟, 余鹏飞, 余建胜, 王东振, 陈威, 乔学军   

  1. 中国地震局地震研究所, 地震大地测量重点实验室, 武汉 430071
  • 收稿日期:2022-11-29 修回日期:2023-02-04 出版日期:2023-10-20 发布日期:2023-11-23
  • 通讯作者: 赵斌, 男, 1981年生, 研究员, 硕士生导师, 现主要从事采用震后形变资料探测断层面摩擦特性和区域岩石圈流变结构研究, E-mail: zhaobin@cgps.ac.cn
  • 作者简介:

    陈毅, 男, 1997年生, 现为中国地震局地震研究所大地测量学与测量工程专业在读研究生, 研究方向为InSAR和GPS地壳形变观测, E-mail:

  • 基金资助:
    中国地震局地震科技星火计划项目(XH21020)

INTERSEISMIC SLIP RATES AND SHALLOW CREEP ALONG THE NORTHWESTERN SEGMENT OF THE XIANSHUIHE FAULT FROM INSAR DATA

CHEN Yi(), ZHAO Bin*(), XIONG Wei, WANG Wei, YU Peng-fei, YU Jian-sheng, WANG Dong-zhen, CHEN Wei, QIAO Xue-jun   

  1. Key Laboratory of Earthquake Geodesy, Institute of Seismology, China Earthquake Administration, Wuhan 430071, China
  • Received:2022-11-29 Revised:2023-02-04 Online:2023-10-20 Published:2023-11-23

摘要:

作为中国大陆最为活跃的断裂带之一, 鲜水河断裂现今的滑动模式, 尤其是北西段的浅部蠕滑特征长期以来备受关注。文中首先利用Sentinel-1卫星降轨数据, 基于小基线集时序分析(SBAS)方法获取鲜水河断裂带北西段2014—2021年的地表视线向(LOS向)平均速度场; 再采用弹性螺旋位错模型拟合InSAR跨断层剖面速度, 估计断层的长期滑动速率和浅部蠕滑速率; 最后结合黏弹性地震周期模型分析炉霍段地震的复发周期、 下地壳和上地幔流变对滑动速率估计的影响。InSAR处理结果显示, 断层两侧LOS向速度场呈现出明显的速度差异。使用弹性螺旋位错模型估计得到的鲜水河断裂北西段的断层滑动速率为7.2~11.0mm/a, 自西向东逐渐减小。断裂带浅部蠕滑速率为0.3~3.1mm/a, 蠕滑主要集中在虾拉沱和道孚—松林口之间。基于历史地震的复发周期及青藏高原东缘下地壳和上地幔黏滞系数的研究, 文中采用黏弹性地震周期模型反演得到炉霍段的滑动速率为(7.91±0.3)~(9.85±0.4)mm/a, 略低于纯弹性螺旋位错模型的结果((10.14±0.5)mm/a)。

关键词: 鲜水河断裂带, 震间滑动速率, 浅部蠕滑, 黏弹性地震周期模型

Abstract:

Located in the eastern boundary of the Qinghai-Tibetan plateau, the Xianshuihe fault zone is one of the most active left-lateral strike-slip faults in Chinese mainland. As the southern boundary of the Bayanhar block, the Xianshuihe Fault accommodates the southeastward transport of material toward southeastern Asia. Earthquakes have occurred frequently along this fault, especially in the northwestern segment. More than 20 earthquakes with MW>6.0 have ruptured since 1700. The most recent MW>7 earthquake was the Luhuo earthquake in 1973, and the most recent MW>6 earthquake was the MW6.6 Luding earthquake in 2022. As one of the most active faults in mainland China, the present slip pattern of the Xianshuihe Fault, especially the shallow creep characteristics along its northwestern segment, has attracted much attention.

The primary goal of determining slip rates of active faults using geodetic data is to quantify the seismic potential of the faults. Illuminating the long-term slip rate and shallow creep distribution of faults is the basis for calculating the seismic moment rate and evaluating the seismic potential. Due to the backwardness of early measurement methods, the seismic deformation along the Xianshuihe Fault was previously based on geologic, cross-fault short baseline and leveling surveys. With the application of GPS in tectonic geodesy, more and more GPS stations are installed near active faults, which provide accurate constraints on the long-term slip rates of the fault. Subsequently, the appearance of InSAR technology has brought a beneficial supplement to GPS, providing high spatial resolution surface velocity maps, which have been widely used to measure deep and shallow creep along active faults. It is the key to accurately characterize the fault slip behavior and evaluate the seismic potential.

In this study, 119 Sentinel-1 satellite descent data from December 2014 to December 2021 were processed to obtain the average line-of-sight(LOS)velocity field of the northwestern segment of the Xianshuihe Fault based on the small baseline InSAR method. Then the elastic screw dislocation model was used to fit the fault normal InSAR LOS velocity profiles to estimate the long-term slip rates and shallow creep rates. Combined with the viscoelastic earthquake cycle model, the effects of the earthquake recurrence period, and rheology of the lower crust and upper mantle on slip rate estimation in Luhuo segment are analyzed. The main results are as follows:

(1)The average InSAR LOS velocity field is in the northwestern segment of the Xianshuihe Fault during 2014—2021 has been obtained with a large range and high spatial resolution. The velocity field results show an obvious velocity gradient across the surface trace of the Xianshuihe Fault, which is consistent with the left-lateral strike-slip characteristics of the Xianshuihe Fault.

(2)To investigate the slip rate variation along the northwestern segment of the Xianshuihe Fault, we used the two-dimensional elastic screw dislocation model to fit the 14 fault-normal velocity profiles selected along the northwestern segment of the Xianshuihe Fault and estimated the long-term slip rates and shallow creep rates using the Markov Chain Monte Carlo(MCMC)method. The results show that the overall slip rates of the NW segment of the Xianshuihe Fault range from 7.2mm/a to 11.0mm/a, and gradually decrease from west to east. The shallow creep rate ranges from 0.3mm/a to 3.1mm/a. The high creep rate appears mainly at Xialatuo and the segment from Daowu to Songlinkou. The shallow creep rates in other places are close to zero, implying that the fault is completely locked.

(3)According to historical earthquake records, the recurrence interval of the Luhuo segment is set to be 150 years, 200 years, and 400 years, and the viscosity of the lower crust and upper mantle is set to be 5.0×1018Pa·s, 1.0×1019Pa·s, and 5.0×1019Pa·s. The slip rate of the Luhuo segment is estimated to be (7.91±0.3)~(9.85±0.4)mm/a using the MCMC method, which is slightly lower than the (10.14±0.5)mm/a obtained by the pure elastic model. In addition, when the earthquake recurrence interval is 150 years and the viscosity of the lower crust and upper mantle is 5.0×1019Pa·s, we simulate the fault-normal velocity at 5 years, 20 years, 75 years, and 125 years after the 1973 Luhuo earthquake, and find that in any period of the seismic cycle, the estimation of fault slip rate will be biased to some extent if the viscoelastic contribution of the lower crust and upper mantle is ignored.

Key words: Xianshuihe Fault, inter-seismic slip rate, shallow creep, viscoelastic earthquake cycle model