COSEISMIC DISPLACEMENT MEASUREMENT AND DISTRIBUTED DEFORMATION CHARACTERIZATION: A CASE OF 2021 MW7.4 MADOI EARTHQUAKE

doi:10.3969/j.issn.0253-4967.2022.02.014

SEISMOLOGY AND GEOLOGY ›› 2022, Vol. 44 ›› Issue (2): 506-523.DOI: 10.3969/j.issn.0253-4967.2022.02.014

• Focus: Mechanical understanding of the surface ruptures of the 2021 Madoi earthquake • Previous Articles Next Articles

COSEISMIC DISPLACEMENT MEASUREMENT AND DISTRIBUTED DEFORMATION CHARACTERIZATION: A CASE OF 2021 M_W7.4 MADOI EARTHQUAKE

SHAO Yan-xiu¹⁾(), LIU-ZENG Jing¹^,²⁾^,^*(), GAO Yun-peng¹⁾, WANG Wen-xin¹⁾, YAO Wen-qian¹⁾, HAN Long-fei¹⁾, LIU Zhi-jun¹⁾, ZOU Xiao-bo³⁾, WANG Yan¹⁾, LI Yun-shuai¹⁾, LIU Lu⁴⁾

1) Institute of Surface-Earth System Science, School of Earth System Science, Tianjin University, Tianjin 300072, China
2) State Key Laboratory of Earthquake Dynamics, Institute of Geology, China Earthquake Administration, Beijing 100029, China
3) Gansu Lanzhou Geophysics National Observation and Research Station, Lanzhou 730000, China
4) Lanzhou Institute of Geotechnique and Earthquake, China Earthquake Administration, Lanzhou 730000, China

Received:2022-01-25 Revised:2022-03-20 Online:2022-04-20 Published:2022-06-14
Contact: LIU-ZENG Jing

同震地表破裂的位移测量与弥散变形分析——以2021年青海玛多M_W7.4地震为例

邵延秀¹⁾(), 刘静¹^,²⁾^,^*(), 高云鹏¹⁾, 王文鑫¹⁾, 姚文倩¹⁾, 韩龙飞¹⁾, 刘志军¹⁾, 邹小波³⁾, 王焱¹⁾, 李云帅¹⁾, 刘璐⁴⁾

1)天津大学, 地球系统科学学院, 表层地球系统科学研究院, 天津 300072
2)中国地震局地质研究所, 地震动力学国家重点实验室, 北京 100029
3)兰州地球物理国家野外科学观测研究站, 兰州 730000
4)中国地震局兰州岩土地震研究所, 兰州 730000

通讯作者: 刘静
作者简介:邵延秀, 男, 1984年生, 2018年于中国地震局地质研究所获构造地质专业博士学位, 副教授, 主要从事活动构造和构造地貌方面的研究工作, E-mail: shaoyx@tju.edu.cn。
基金资助:
国家自然科学基金(42011540385);国家自然科学基金(U1839203);中国博士后科学基金(2021M702425)

Abstract

Abstract:

The coseismic displacements are required to characterize the earthquake rupture and provide basic data for exploring the faulting mechanism and assessing seismic risk in the future. Detailed field investigation is still an important way to acquire reliable coseismic displacements comparing to geodetic measurements. Combining with previous research on other earthquakes, this study tries to discuss distributed deformation along the strike rupture and its implications. The M_W7.4 Madoi earthquake ruptured the southeast section of the Kunlun Shankou-Jiangcuo Fault on May 22, 2021, in Qinghai Province. It is a typical strike slip event, and its epicenter locates at~70km south of the East Kunlun Fault, which is the north boundary of the Bayan Har block. Field investigation results show that the surface rupture extends along the piedmont. The deformation features mainly include compression humps, extensional and shear fissures, and scarps. After the earthquake, we used the unmanned aerial system to survey the rupture zone by capturing a swath of images along the strike. The swath is larger than 1km in width. Then we processed the aerial images by commercial software to build the orthoimage and the digital elevation model(DEM)with high resolutions of 3~5cm. We mapped the surface rupture in detail based on drone images and DEM along the western section. Meanwhile, we also got the commercial satellite images captured before the earthquake, on 2nd January 2021. The images were processed with geometrical rectification before comparison. The spatial resolution of satellite images before earthquake is about 0.5m.
At the south of the Eling Hu(Lake), the clear offset tire tracks provide an excellent marker for displacement measurement. We located the positions of tracks precisely based on remote sensing images, and compared between the tracks lines after earthquake and the corresponding positions before earthquake, then extracted distance difference, which is defined as coseismic displacements. The results show that the total displacement is about 3.6m, which contains the distributed deformation of about 0.9m. The off-fault deformation is about 33% of the on-fault and about 25% of the total deformation. The ratios are similar to previous studies on earthquake worldwide. The fault zone width is probable about 200m. The total horizontal displacement measured by this study is similar to the slip in depth by InSAR inversion, which implies that there is no slip deficit at the west rupture section of the earthquake.
The results also present the asymmetry of distributed deformation that most distributed deformation occurs at the south of the surface rupture zone. Comparing with other earthquakes in the world, it is likely that the asymmetrically distributed deformation is common in strike-slip earthquakes and the asymmetric feature is not related to the property of the material. The characteristics of distributed deformation might be related to fault geometry at depth or local stress state. More work is needed to resolve this question in the future. This study implies that we probably underestimated the slip rates resulting from ignoring distributed deformation in the past. In order to avoid underestimation of slip rates, we can correct the previous results by the ratio of distributed deformation to total slip. It is also suggested that the study sites should be on the segment with narrow deformation and simple geometry.

Key words: Madoi earthquake, coseismic displacement, distributed deformation, strike-slip fault, slip rate

摘要：

同震位移作为量化地震破裂特征的基本参数, 可为探究断裂活动机制和预测未来地震危险性提供重要的约束条件。尽管大地测量技术能够快速刻画地震在时空上的破裂特征, 然而详细的野外实地调查与测量仍然是获得可靠同震位移和提取弥散变形特征最有效的方法。文中以2021年青海玛多 M_W7.4 地震为例, 基于无人机正射影像, 对破裂带进行了详细的解译, 并结合国外震例的研究结果探讨了走滑地震的弥散变形特征及其意义。玛多地震的发震断裂为左旋走滑性质的昆仑山口-江错断裂的东南段, 其地表破裂带在西段整体沿山前或山麓地带展布, 主要是由挤压鼓包、张剪裂缝和断层陡坎等沿近EW向雁列组合而成的左旋剪切破裂带。结合震前卫星影像, 对该破裂带西段较大位移点的鄂陵湖南侧断错车轮印迹线进行了震前和震后的精细填绘与对比分析。结果表明, 该段同震变形在主破裂带南侧存在弥散变形现象, 重新恢复获得的总左旋位移量约为3.6m, 其中主变形位移量约为2.7m, 弥散变形量约为0.9m, 占主变形位移量的33%。综合分析后认为, 弥散变形在走滑型同震破裂带上可能普遍存在, 而且往往具有不对称性。新的研究结果指示, 在走滑断层的滑动速率研究中, 观测点应尽量选在几何结构简单的区段, 从而减少弥散变形的影响。

关键词: 玛多地震, 同震位移, 弥散变形, 走滑断裂, 滑动速率

CLC Number:

P315.2

SHAO Yan-xiu, LIU-ZENG Jing, GAO Yun-peng, WANG Wen-xin, YAO Wen-qian, HAN Long-fei, LIU Zhi-jun, ZOU Xiao-bo, WANG Yan, LI Yun-shuai, LIU Lu. COSEISMIC DISPLACEMENT MEASUREMENT AND DISTRIBUTED DEFORMATION CHARACTERIZATION: A CASE OF 2021 M_W7.4 MADOI EARTHQUAKE[J]. SEISMOLOGY AND GEOLOGY, 2022, 44(2): 506-523.

邵延秀, 刘静, 高云鹏, 王文鑫, 姚文倩, 韩龙飞, 刘志军, 邹小波, 王焱, 李云帅, 刘璐. 同震地表破裂的位移测量与弥散变形分析——以2021年青海玛多M_W7.4地震为例[J]. 地震地质, 2022, 44(2): 506-523.

Figures/Tables 9

Fig. 1 Active tectonics around the Madoi earthquake rupture zone.

Fig. 2 Rupture mapping along the western segment (south of the Eling Hu) of the Madoi earthquake.

Fig. 3 Remote sensing images before and after Madoi earthquake.

Fig. 4 The western segment of surface rupture of the Madoi earthquake at the south of the Eling Hu.

Fig. 5 Tire tracks mapping before and after the earthquake.

Fig. 6 Measurements of movement of tire tracks.

Fig. 7 Movements of tire tracks at the south of surface rupture after the earthquake.

Fig. 8 Coseismic displacements of 1999 Izmit-Düzce earthquakes in Turkey(modified from Rockwell et al., 2002).

Fig. 9 Coseismic displacement of 1999 Hector Mine earthquake in the US (modified from Treiman et al., 2002).

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