SEISMOGENIC STRUCTURE OF THE DINGRI MW5.7 EARTH-QUAKE OF MARCH 20, 2020 (SOUTHERN QINGHAI-XIZANG PLATEAU) CONSTRAINED BY THE COSEISMIC AND POSTSEISMIC DEFORMATION

doi:10.3969/j.issn.0253-4967.2025.04.20240061

Abstract

Abstract:

On 20 March 2020, an M_W5.7 shallow normal-faulting earthquake struck the Shenzha-dingjie fault zone, southern Xizang, providing a significant opportunity to understand the regional seismogenic structure in the little-studied area using the modern satellite geodetic technology. The ascending and descending SAR images from the Sentinel-1A satellite are utilized to derive both the coseismic LOS deformation and the first half-year postseismic LOS deformation associated with this earthquake. The ranges of the coseismic LOS displacements in the ascending and descending interferograms are -13.6 to 2.8cm and -14.6 to 2.2cm, respectively, while the range of the postseismic LOS displacements in the ascending interferograms is -4.8 to 2.6cm. Our coseismic modeling result shows that the earthquake nucleated on a previously unidentified normal fault buried at depths of 1.6 to 5.7m, and that the maximum coseismic slip of ~0.85m is located at a depth of ~4.7km. The coseismic slip distribution model generated a seismic moment of ~3.65×10¹⁷N·m, equivalent to a moment magnitude(M_W)of 5.7. The result of the postseismic deformation throughout nearly half a year following the mainshock shows that the deformation magnitude gradually increases over time and that the deformation increased significantly in the first three months, while the increase trend was relatively slow in the later period. The ranges of the cumulative postseismic surface deformation are -4.8 to 2.6cm. In-depth postseismic analysis reveals that postseismic afterslip and coseismic slip are located at the same fault plane and that the postseismic slip limited to a depth of 0.8 to 4.8km, lies in the up-dip area of the coseismic slip. The seismic moment released by postseismic slip distribution is ~7.8×10¹⁶N·m, corresponding to an M_W5.2 earthquake. The peaking postseismic slip of ~0.23m is located at a depth of ~2km. The deep coseismic slip and shallow postseismic afterslip of this earthquake image an almost complete single planar seismogenic fault structure. By a comprehensive analysis of the inversions, regional topography, landforms and active fault kinematics, we conclude that contrasts in the gravitational potential energy of the regional structure may be the main cause of this earthquake. In addition, coseismic Coulomb stress modelling shows the fairly strong stress loading at both the southern and northern branch fault segments of the Shenzha-dingjie fault zone, with the stress values reaching 0.04MPa and 0.18MPa, respectively. Given that these two branch faults exhibit relatively large positive Coulomb failure stress changes without seismicity during and after this earthquake, the risk associated with these two faults should be given attention. This study demonstrates that the combined data of coseismic and postseismic surface deformation can precisely detect the underground seismogenic fault structure of the hidden normal-faulting earthquake.

Key words: Southern Qinghai-Xizang Plateau, Dingri earthquake, coseismic deformation, postseismic deformation, planar normal fault, gravitational potential energy

摘要：

2020年3月20日, 青藏高原南部申扎-定结断裂带附近发生了一次 M_W5.7 浅源地震, 为通过现代卫星大地测量技术探究该研究程度较低区域的发震构造提供了机会。文中利用Sentinel-1A卫星升、降轨SAR影像获取了该地震同震及震后半年的地表形变。同震模拟结果揭示地震成核于一条埋深于1.6~5.7km深度的之前未被识别的正断层。深入的震后分析表明震后余滑与同震滑动孕育于同一断层面, 且位于其上倾0.8~4.8km深度处。该地震深部同震滑动及浅部余滑共同成像一条近完整的单平面地下发震断层。通过对反演结果、地形地貌及断层特性的分析, 推断构造区域内较高的重力势能差可能是地震发生的主因。同震库仑应力模拟显示, 申扎-定结断层带南、北分支断层表现较强的应力加载, 应注意其破裂风险。

关键词: 青藏高原南部, 定日地震, 同震形变, 震后形变, 平面状正断层, 重力势能

YANG Jiu-yuan, WEN Yang-mao, XU Cai-jun, YANG Jian-bing. SEISMOGENIC STRUCTURE OF THE DINGRI M_W5.7 EARTH-QUAKE OF MARCH 20, 2020 (SOUTHERN QINGHAI-XIZANG PLATEAU) CONSTRAINED BY THE COSEISMIC AND POSTSEISMIC DEFORMATION[J]. SEISMOLOGY AND GEOLOGY, 2025, 47(4): 1292-1305.

杨九元, 温扬茂, 许才军, 杨见兵. 同震及震后形变约束的2020年3月青藏高原南部定日 M_W5.7 地震发震构造[J]. 地震地质, 2025, 47(4): 1292-1305.

Figures/Tables 9

Fig. 1 Geological structural map of the Qinghai-Xizang Plateau, its southern margin and 2020 Dingri earthquake.

Table1 Source parameters of the 2020 Dingri earthquake

来源	东经 /(°)	北纬 /(°)	走向 /(°)	倾角 /(°)	滑动角 /(°)	长 /km	宽 /km	震级 /M_W
USGS	87.308	28.59	343、180	49、42	-101、-77			5.7
GCMT	87.42	28.51	345、184	45、47	-103、-77			5.7
前人模型^①	87.405	28.664	318.6	43.6	-114	4.2	4.7	5.7
前人模型^②	87.392	28.66	330	62.7	-104.6	3.0.	3.1.	5.6
前人模型^③	87.403	28.657	334.2	50.6	-106.9	3.0	2.7	5.6
本文模型	87.40	28.665	329	54.0	-121	3.9		5.65

Fig. 2 Ascending and descending coseismic downsampled data, interferograms, LOS deformation, and the LOS displacements along the profile AB and CD.

Fig. 3 Ascending postseismic deformation time series of the March 20, 2020 Dingri earthquake.

Fig. 4 Geometrical parameters for the uniform fault plane of the 2020 Dingri earthquake through the Monte-Carlo method and the map of smoothing factor selection during the linear inversion.

Fig. 5 Coseismic slip distribution of the 2020 Dingri earthquake and the profile map of the subsurface fault structure.

Fig. 6 Ascending and descending coseismic interferogram, modelling, and residual maps of the 2020 Dingri earthquake.

Fig. 7 The maps of the modelled surface deformation due to poroelastic rebound, postseismic afterslip distribution, and postseismic observation, modelling, and residual data.

Fig. 8 Coseismic coulomb stress changes along the nearby active faults induced by the 2020 Dingri earthquake.

References 28

[1]	李琦, 李承涛, 赵斌, 等. 2024. 2020年西藏定日 M_W5.6 地震震源参数估计和应力触发研究[J]. 地球物理学报, 67(1): 172—188.
	LI Qi, LI Cheng-tao, ZHAO Bin, et al. 2024. Estimated seismic source parameters for 2020 Dingri M_W5.6 earthquake in Xizang and study on the stress triggering[J]. Chinese Journal of Geophysics, 67(1): 172—188 (in Chinese).
[2]	王永哲, 陈石, 陈鲲. 2021. InSAR数据约束的2020年西藏定日 M_W5.7 地震源模型及构造意义[J]. 地震, 41(1): 116—128.
	WANG Yong-zhe, CHEN Shi, CHEN Kun. 2021. Source model and tectonic implications of the 2020 Dingri M_W7.6 earthquake constrained by InSAR data[J]. Earthquake, 41(1): 116—128 (in Chinese).
[3]	张小涛, 姜祥华, 薛艳, 等. 2020. 2020年3月20日西藏定日 M_S5.9 地震总结[J]. 地震地磁观测与研究, 41(4): 193—203.
	ZHANG Xiao-tao, JIANG Xiang-hua, XUE Yan, et al. 2020. Summary of the Dingri M_S5.9 earthquake in Tibet on March 20, 2020[J]. Seismological and Geomagnetic Observation and Research, 41(4): 193—203 (in Chinese).
[4]	Bie L, Ryder I. 2014. Recent seismic and aseismic activity in the Ashikule stepover zone, NW Tibet[J]. Geophysical Journal International, 198(3): 1632—1643.
[5]	Cavalié O, Doin M P, Lasserre C, et al. 2007. Ground motion measurement in the Lake Mead area, Nevada, by differential synthetic aperture radar interferometry time series analysis: Probing the lithosphere rheological structure[J]. Journal of Geophysical Research, 112(B3): 1—18.
[6]	Doin M P, Lasserre C, Peltzer G, et al. 2009. Corrections of stratified tropospheric delays in SAR interferometry: Validation with global atmospheric models[J]. Journal of Applied Geophysics, 69(1): 35—50.
[7]	Elliott J R, Walters R J, England P C, et al. 2010. Extension on the Tibetan plateau: recent normal faulting measured by InSAR and body wave Seismology[J]. Geophysical Journal International, 183(2): 503—535.
[8]	Fattahi H, Amelung F. 2013. DEM error correction in InSAR time series[J]. IEEE Transactions on Geoscience and Remote Sensing, 51(7): 4249—4259.
[9]	Fattahi H, Amelung F. 2016. InSAR observations of strain accumulation and fault creep along the Chaman Fault system, Pakistan and Afghanistan[J]. Geophysical Research Letters, 43(16): 8399—8406.
[10]	Feng W, Li Z, Elliott J R, et al. 2013. The 2011 M_W6.8 Burma earthquake: Fault constraints provided by multiple SAR techniques[J]. Geophysical Journal International, 195: 650—660.
[11]	Freed A M. 2005. Earthquake triggering by static, dynamic, and postseismic stress transfer[J]. Annual Review of Earth and Planetary Sciences, 33(1): 335—367.
[12]	Furuya M, Yasuda T. 2011. The 2008 Yutian normal faulting earthquake(M_W7.1), NW Tibet: Non-planar fault modeling and implications for the Karakax Fault[J]. Tectonophysics, 511(3-4): 125—133.
[13]	Goldstein R M, Werner C L. 1998. Radar interferogram filtering for geophysical applications[J]. Geophysical Research Letters, 25(21): 4035—4038.
[14]	Goldstein R M, Zebker H A, Werner C L. 1988. Satellite radar interferometry: Two-dimensional phase unwrapping[J]. Radio Science, 23(4): 713—720.
[15]	Li C, Li Q, Tan K, et al. 2022. Ground deformation and source fault model of the M_W5.7 Xegar(Tibetan plateau)2020 Earthquake, based on InSAR observation[J]. Pure and Applied Geophysics, 179: 3589—3603.
[16]	Molnar P, Tapponnier P. 1978. Active tectonics of Tibet[J]. Journal of Geophysical Research: Solid Earth, 83(B11): 5361—5375.
[17]	Okada Y. 1985. Surface deformation due to shear and tensile faults in a half-space[J]. Buletin of the Seismological Society of America, 75(4): 1135—1154.
[18]	Passone L, Mai P M. 2017. Kinematic earthquake ground-motion simulations on listric normal faults[J]. Bulletin of the Seismological Society of America, 107(6): 2980—2993.
[19]	Reynolds K, Copley A. 2018. Seismological constraints on the down-dip shape of normal faults[J]. Geophysical Journal International, 213(1): 534—560.
[20]	Ryder I, Bürgmann R, Sun J. 2010. Tandem afterslip on connected fault planes following the 2008 Nima-Gaize(Tibet)earthquake[J]. Journal of Geophysical Research: Solid Earth, 115(B3): 1—16.
[21]	Wang K, Fialko Y. 2014. Space geodetic observations and models of postseismic deformation due to the 2005 M7.6 Kashmir(Pakistan)earthquake[J]. Journal of Geophysical Research: Solid Earth, 119(9): 7306—7318.
[22]	Wang K, Fialko Y. 2018. Observations and modeling of coseismic and postseismic deformation due to the 2015 M_W7.8 Gorkha(Nepal)earthquake[J]. Journal of Geophysical Research: Solid Earth, 123(1): 761—779.
[23]	Wegnüller U, Werner C, Strozzi T, et al. 2016. Sentinel-1 support in the GAMMA software[J]. Procedia Computer Science, 10: 1305—1312.
[24]	Xu X, Tan X, Yu G, et al. 2013. Normal- and oblique-slip of the 2008 Yutian earthquake: Evidence for eastward block motion, northern Tibetan plateau[J]. Tectonophysics, 584: 152—165.
[25]	Yang J, Xu C, Wen Y, et al. 2021. The July 2020 M_W6.3 Nima earthquake, central Tibet: A shallow normal-faulting event rupturing in a stepover zone[J]. Seismological Research Letters, 93(1): 45—55.
[26]	Yang J, Xu C, Wen Y, et al. 2022. Complex coseismic and postseismic faulting during the 2021 northern Thessaly(Greece)earthquake sequence illuminated by InSAR observations[J]. Geophysical Research Letters, 49(8): 1—10.
[27]	Zhang Y, Fattahi H, Amelung F. 2019. Small baseline InSAR time series analysis: Unwrapping error correction and noise reduction[J]. Computers & Geosciences, 133: 1—19.
[28]	Ziv A, Rubin A M. 2000. Static stress transfer and earthquake triggering: No lower threshold in sight?[J]. Journal of Geophysical Research: Solid Earth, 105(B6): 13631—13642.