STRESS FIELD IN SHANXI RIFT AND ITS DYNAMIC SIGNIFICANCE

doi:10.3969/j.issn.0253-4967.20240030

Abstract

Abstract:

To carry out the more refined structural stress field and its formation mechanism, we mainly use the focal mechanism solution of small-moderate earthquakes since the observation in the Shanxi rift. The statistical results of focal mechanism solution classification show that the main types are strike-slip and normal faulting mechanism, and the percentage of strike-slip faulting, normal faulting and normal with strike-slip component is about 77%, which conforms to the transtensional deformation characteristics in the Shanxi rift. We adopt the damping stress inversion methodand invert stress fieldof the whole domain, 5 Basins, 0.5° grid of spatial distribution. We obtain the stress field parameters and stress shape factor(R value).

This study indicates that the Shanxi rift region is characterized by a NW-SE extensional stress field with localized strike-slip stress regimes, reflecting its heterogeneous nature The inversion result of 724 M_L<3.0 focal mechanisms is normal faulting regime, and the results of 301 M_L≥3.0 focal mechanisms is strike-slip faulting regime. Although there are slight differences in the results of subseismic magnitude categories, the azimuth and plunge angle of σ₃ are mostly similar, which can still reflect the stable NW-SE tensional stress environment. The results also indicate that the Shanxi rift exhibits heterogeneous stress field characteristics, with the northern and southern basins(Yuncheng Basin and Datong Basin) in a strike-slip faulting regime, while the Xinding, Taiyuan, and Linfen Basins are in a normal faulting regime. Generally, this reflects that the stress environment of the Shanxi rift is dominated by tensile forces, accompanied by a shear component.

The 0.5° grid of stress field results show that the azimuth angle of the most tension principal stress σ₃ in the entire area of Shanxi rift is dominated by the NW-SE direction and the plunge of σ₃ is nearly horizontal, which is generally perpendicular to the direction of the main control fault in Shanxi depression basins. While the azimuth angle of σ₁ is roughly parallel to the direction of the main control fault, and the spatial change of the plungeangle is not uniform. The spatial distribution results of stress field generally reflect the stable and horizontal tension, and the local heterogeneous stress field is caused by the changes of the most compressive principalstress σ₁ and the intermediate principal stress σ₂. The spatial distribution of stress field results show that the value of R is mostly less than 0.5, which reflects that intermediate principal stress σ₂ is compressive stress, according with the stress state of Shanxi rift that is dominated by tension accompanied of a shear component.

In addition, the GPS velocity profile results also show that there is a extension movement of about 0.5mm/a in Shanxi rift, and there is local strike-slipping movement. The main crustal deformation of Datong Basin is the NW-SE extension with the a rate of 0.5-1mm/a, including minimal shear or strike-slip component. The main crustal deformation of Taiyuan Basin exhibits the NW-SE extension with 0.3-0.7mm/a, showing weak shear or strike-slip component. The Yuncheng Basin demonstrates both extensional and strike-slip deformation, with an extensional rate of about 0.6mm/a and a dextral strike-sliping rate of about 0.7mm/a. From a relative quantitative perspective, GPS data and other measurement techniques have shown that the Shanxi rift exhibits both extensional and shear deformation characteristics. The Shanxi rift serves as the boundary of a secondary block within the North China block, and its formation and dynamic source are related to the remote action of Pacific plate subduction and Indo-Europe collision extrusion.

Key words: focal mechanism solution, stress field inversion, the depression basin, the Shanxi rift

摘要：

为了开展山西裂谷更精细的构造应力场及其形成机制研究, 文中主要利用山西裂谷自观测以来至今较为丰富的中小地震的震源机制解, 采用阻尼应力反演方法对山西裂谷分别进行全域、分盆地、 0.5° 网格等划分并反演构造应力场, 得到应力场参数和应力形因子(R值)。结果表明, 山西裂谷全域的构造应力场总体为NW-SE向拉张型应力场, 局部存在走滑型应力场; 分盆地结果也显示山西裂谷呈现非均匀的应力场特征, 南、北两端盆地(运城盆地和大同盆地)为走滑型应力场, 中部忻定、太原、临汾盆地为拉张型应力场。0.5° 网格的应力场结果表明, σ₃的方位以NW-SE向为主, 倾伏角近水平, 与山西断陷盆地主控断裂的走向大体垂直, 而σ₁的方位则大体平行于主控断裂走向, 倾伏角空间变化不均匀。此外, GPS速度剖面结果也显示山西裂谷现今存在约0.5mm/a的拉张运动, 且局部有走滑运动。从相对定量的角度, 二者都反映出山西裂谷拉张剪切变形的特征。这与太平洋板块俯冲和印欧大陆碰撞挤压的远程作用相关。

关键词: 震源机制解, 应力场反演, 断陷盆地, 山西裂谷

WANG Xia, SONG Mei-qing, WU Hao-yu, LIANG Xiang-jun, LÜ Rui, GUO Wen-feng, ZHANG Na, LI Jin. STRESS FIELD IN SHANXI RIFT AND ITS DYNAMIC SIGNIFICANCE[J]. SEISMOLOGY AND GEOLOGY, 2026, 48(1): 257-277.

王霞, 宋美卿, 吴昊昱, 梁向军, 吕睿, 郭文峰, 张娜, 李金. 山西裂谷构造应力场特征及其动力学意义[J]. 地震地质, 2026, 48(1): 257-277.

Figures/Tables 18

Fig. 1 The spatial distribution of focal mechanism solutions of earthquakes in Shanxi rift.

Table1 The classification of focal mechanism solutions of small-moderate earthquakes in Shanxi rift

类别	正断型	正走滑型	走滑型	逆走滑型	逆断型	合计	数据
次数/次	300	130	363	95	137	1025	山西全部数据
比例	29.27%	12.68%	35.41%	9.27%	13.37%	100%
次数/次	230	93	229	59	113	724	山西地区M_L<3.0
比例	31.77%	12.85%	31.63%	8.15%	15.61%	100%
次数/次	70	37	134	36	24	301	山西地区M_L≥3.0
比例	23.26%	12.29%	44.52%	11.96%	7.97%	100%

Fig. 2 The focal mechanism solution classification of small-moderate earthquakes in Shanxi rift.

Fig. 3 The damping curve.

Table2 The parameters of tectonic stress field in Shanxi rift and 5 basins

区域	R	σ₁		σ₂		σ₃		类型
区域	R	方位角/(°)	倾伏角/(°)	方位角/(°)	倾伏角/(°)	方位角/(°)	倾伏角/(°)	类型
山西地区所有数据	0.11	143.56	-89.08	58.96	0.09	148.96	0.92	NF
山西地区M_L≥3.0	0.10	58.83	14.88	64.67	-75.05	149.22	1.45	SS
山西地区M_L<3.0	0.21	65.89	-82.34	56.95	7.57	147.11	1.18	NF
大同盆地	0.32	51.13	-34.12	54.30	55.84	142.13	-1.47	SS
忻定盆地	0.28	73.24	76.78	46.47	-11.84	137.69	-5.78	NF
太原盆地	0.34	56.55	77.80	72.39	-11.75	161.72	3.24	NF
临汾盆地	0.06	59.62	-53.26	53.83	36.60	145.89	2.78	NF
运城盆地	0.68	64.8	38.73	44.81	-49.52	146.70	-9.97	SS

Fig. 4 The main axis of stress field and R frequency in Shanxi rift(all data).

Fig. 5 The main axis of stress field and R frequency in Shanxi rift(ML<3.0 earthquakes).

Fig. 6 The main axis of stress field and R frequency in Shanxi rift(ML≥3.0 earthquakes).

Fig. 7 The main axis of stress field and R frequency in Datong Basin, Shanxi rift.

Fig. 8 The main axis of stress field and R frequency in Xinding Basin, Shanxi rift.

Fig. 9 The main axis of stress field and R frequency in Taiyuan Basin, Shanxi rift.

Fig. 10 The main axis of stress field and R frequency in Linfen Basin, Shanxi rift.

Fig. 11 The main axis of stress field and R frequency in Yuncheng Basin, Shanxi rift.

Fig. 13 The spatial distribution of stress field (σ1 and σ3)and R in Shanxi rift.

Fig. 13 The location of GPS velocity profile in the Shanxi rift.

Fig. 14 The GPS velocity profile of Kouquan Fault in Datong Basin.

Fig. 15 The GPS velocity profile of Jiaocheng Fault in Taiyuan Basin.

Fig. 16 The GPS velocity profile of Zhongtiaoshan Fault in Yuncheng Basin.

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