2021年5月21日云南漾濞M6.4地震序列的矩心矩张量解及动力环境分析

doi:10.3969/j.issn.0253-4967.2021.04.005

摘要/Abstract

摘要：

文中利用中国地震台网中心汇编的震相数据, 基于2021年5月18-28日云南漾濞地震周边101个地震台站的观测数据, 采用双差定位方法对漾濞地震的前震-主震-余震序列进行了精定位研究, 获得了2 144个地震的精确位置。对结果进行分析后发现, 此次地震的主余震分布、烈度等震线长轴方位与维西-乔后断裂的位置并不一致, 且走向与其呈小角度相交, 推断该地震的发震断裂可能是维西-乔后断裂的次级断裂或其他未知断裂。在精定位结果的基础上, 采用贝叶斯自助优化BABO(Bayesian Bootstrap Optimisation)算法对2021年5月18-28日云南漾濞M6.4地震和M≥3.6地震序列进行了矩张量反演, 结果表明, 云南漾濞地震序列具有明显的分段性。漾濞M6.4主震为右旋走滑型兼有少量正倾分量, 矩心深度为5.9km, 大多数余震与主震的机制一致, 以右旋走滑为主, 只是在余震区的东南段西分支处震源性质有明显的不同, 为正走滑型。整个地震序列的矩心深度为3.5~8.2km。应力场反演结果显示, 震区主压应力场近SN向、走向滑动错动类型略带正倾分量。从地震序列分布和应力方向来看, 本次地震的主要动力来源可能是川滇地块向SE的挤出作用, 地震破裂过程和破裂样式代表了川滇地块挤出后的 “松弛”过程。从构造背景上看, 本次漾濞地震可能是在川滇地块向SE挤出和印度板块向W后撤(或者地幔底侵)2种动力环境下发生的。

关键词: 云南漾濞地震, 维西-乔后断裂, 地震精定位, 应力场, 矩张量解

Abstract:

According to the Unified Earthquake Catalogue of China Earthquake Networks, using the seismic phase data compiled by the Seismic Data Center, the observations of 101 fixed and mobile seismic stations in the Yunnan region and its surrounding seismic network from May 18 to 28, 2021, we conducted precise positioning research on the foreshock-mainshock-aftershock sequence of the Yangbi earthquake using the double-difference positioning method, and obtained the precise locations of 2 144 earthquakes. It is found that the distribution of the main aftershocks and the long axis orientation of the intensity isoseismal are not consistent with the image position of the Weixi-Qiaohou Fault, and the strike intersects with a small angle. The seismogenic fault of this earthquake may be a secondary fault of the Weixi-Qiaohou Fault. On the basis of the precision positioning results, the Bayesian Bootstrap Optimization(BABO)algorithm is used to perform a moment tensor inversion on the M6.4 earthquake and the M3.6 and above earthquake sequences in Yangbi, Yunnan from May 18 to 28, 2021. The results show that the sequence of Yangbi earthquake in Yunnan has obvious segmentation. The M6.4 Yangbi main shock is of right-handed strike-slip type with a small amount of normal dip-slip component, and the centroid depth is 5.9km. Most aftershocks have the same focal mechanism as the main shock, mainly right-handed strike-slip, except for the earthquakes in the west branch of the southeast section of the aftershock area, where the source property is obviously different, showing a normal strike-slip motion. The centroid depth of the entire earthquake sequence is 3.5~8.2km. The inversion results show that the principal compressive stress field of the earthquake area is in the near NS direction and the strike-slip dislocation is associated with a slight normal dip-slip component.

The spatial distribution of earthquakes shows that this earthquake sequence gradually developed from NW to SE, and the seismic density gradually dispersed from NW to SE. Therefore, it can be considered that the stress was mainly concentrated in the NW direction before the earthquake, and then gradually spread to the SE. Therefore, the main power source of this earthquake may be the southeastward extrusion of the Sichuan-Yunnan block. The rupture process and rupture pattern of this earthquake represents the “relaxation” process of the Sichuan-Yunnan rhombic block after being extruded.

The southern part of the Sichuan-Yunnan block is the material diffusion zone resulting from the eastward extrusion of Qinghai-Tibet Plateau. In this area, the subduction and westward retreat of the Indian plate led to the absence of lateral restraint on the Sichuan-Yunnan block, which may be the main reason causing the earthquake sequences in this area changing from convergence to dispersion, from strike-slip to normal fault type.

The Sichuan-Yunnan block is one of the most insensive areas where the Qinghai-Tibet Plateau squeezes out and escapes southeastward. Regarding the regional dynamic mode, we believe that under the background of continuous eastward extrusion of the material in the eastern part of the Qinghai-Tibet Plateau, and due to the lack of rigid blocks in the horizontal direction, it is more prone to velocity migration in the horizontal direction when the Sichuan-Yunnan block extrudes in the direction of SE and crosses the eastern structural junction and Longmen Mountains. The velocity migration in the study area may be caused by plate subduction or mantle underplating. The study of the lithospheric structure in the Sichuan-Yunnan area found that the crustal thickness of the sub-blocks in central Yunnan gradually thinned from north to south, and the lithospheric thickness in the area west of the Honghe fault zone shows a gradual thinning trend from east to west. It may be related to the intrusion of hot mantle material caused by the subduction and westward retreat of the Indian plate. Tomography results show that in the Ailaoshan-Honghe fault zone, the Yangtze block subducted downwards accompanied by mantle disturbance and asthenosphere upwelling, which led to magmatic activity and intrusion in the Cenozoic. Both of the above two effects can make the western boundary of the Sichuan-Yunnan block have a tensile stress background, and make the focal mechanism of major earthquakes on the nearby tectonic belt possible to appear normal. In summary, the dynamic source of earthquakes in the study area mainly comes from the escape of the Sichuan-Yunnan block to the southeast, and plate subduction or mantle underplating is possibly the deep-seated dynamic background for the lateral velocity migration of the study area.

Key words: Yunnan Yangbi earthquake, Weixi-Qiaohou Fault, precise location of earthquake, stress field, moment tensor solution

中图分类号:

P315.2

郭祥云, 尹海权, 汪贞杰, 杨辉. 2021年5月21日云南漾濞M6.4地震序列的矩心矩张量解及动力环境分析[J]. 地震地质, 2021, 43(4): 806-826.

GUO Xiang-yun, YIN Hai-quan, WANG Zhen-jie, YANG Hui. EARTHQUAKE CENTROID, SEISMIC MOMENT TENSOR AND DYNAMIC ENVIRONMENT ANALYSIS OF THE M_S6.4 EARTHQUAKE SEQUENCE IN YANGBI, YUNNAN ON MAY 21, 2021[J]. SEISMOLOGY AND EGOLOGY, 2021, 43(4): 806-826.

图/表 17

图1 云南漾濞M6.4地震的烈度图

Fig. 1 Intensity map of Yangbi M6.4 earthquake in Yunnan Province.

图2 云南漾濞M6.4地震震中、周围台站分布、主要活动断裂及7.0级以上历史地震的震源机制解红色五角星为震中位置, 蓝色三角为台站, 紫色圆圈为历史地震, 蓝色震源球为历史地震的震源机制解

Fig. 2 Distribution of epicenter and surrounding stations and main active faults of Yangbi M6.4 earthquake in Yunnan Province, and the focal mechanism of earthquakes with M≥7.0 in history.

表1 一维速度模型

Table1 One-dimensional velocity model used in earthquake relocation

地壳厚度/km	0	5	10	16	28	35
V_P/km·s^-1	4.90	5.85	6.12	6.34	6.65	7.10

图3 频域余弦窗函数

Fig. 3 Frequency domain cosine flanked window function.

图4 漾濞6.4级地震序列的精定位分布绿色圆形为M<2地震, 褐色圆形为2≤M<3地震, 橘黄色圆形为3≤M<4地震, 黄色圆形为4≤M<5地震, 蓝色圆形为5≤M<6地震, 红色五角星为主震, 紫色矩形方框表示分区

Fig. 4 Relocation distribution of the May 21, 2021 Yangbi M6.4 earthquake sequence in Yunnan Province.

表2 速度模型

Table2 Velocity structure model

厚度/km	纵波速度/km·s^-1	横波速度/km·s	密度/g·cm^-3
0.00	1.50	0.00	1.02
0.00	3.81	1.94	0.92
0.50	2.50	1.20	2.10
0.00	4.00	2.10	2.40
1.80	6.10	3.50	2.75
1.60	6.30	3.60	2.80
8.50	7.20	4.00	3.10

图5 2021年5月21日漾濞M6.4地震的矩张量解在Hudson震源类型图上的投影 DC 双力偶; +Crack 张裂缝; -Crack 闭合裂缝; +Isotropic 爆炸; -Isotropic 塌陷; ±CLVD 错动方向相反补偿线性失量偶极子; ±Dipole 错动方向相反的偶极子

Fig. 5 Projection of May 21, 2021 Yangbi M6.4 earthquake moment tensor solution on Hudson source type diagram.

图6 2021年5月21日云南漾濞M6.4地震部分台站波形拟合情况红色为实际观测波形, 黑色为理论计算波形。图形左上第1行为台站的名称及分量, 第2行为震中距, 第3行是相对于震源的台站方位角; 图形下方的数字分别为目标权重、目标失配及波形相对于开始时间的起始时间; 背景灰色区域显示应用的锥形函数; 底部小图中红色填充的部分为时域理论波形与实际观测波形之间的幅度残差

Fig. 6 Fits_waveform_ensemble of some stations.

图7 漾濞M6.4地震的矩心位置红色为最佳的双力偶解, 浅红色为低misfit的双力偶解, 蓝色为高misfit的双力偶解

Fig. 7 Earthquake MT_location of Yangbi earthquake.

表3 云南漾濞M6.4地震序列的震源参数

Table3 Source parameters of Yangbi M6.4 earthquake sequence in Yunnan Province

日期	时间	北纬 /(°)	东经 /(°)	深度 /km	震级 M	矩心深度 /km	矩震级 M_W	走向 /(°)	倾角 /(°)	滑动角 /(°)	精定位后北纬 /(°)	精定位后东经 /(°)	序号
2021-05-18	20:56: 46	25.65	99.93	8.0	3.6	6.26	3.7	132	86	-163	25.62	99.93	1
2021-05-18	21:39: 35	25.65	99.93	8.0	4.7	5.35	4.4	308	82	162	25.63	99.93	2
2021-05-19	03:27: 56	25.65	99.92	8.0	3.7	4.95	3.8	314	80	172	25.63	99.92	3
2021-05-19	21:13: 07	25.68	99.89	8.0	3.8	4.79	4.0	312	83	179	25.66	99.89	4
2021-05-20	01:58: 59	25.67	99.90	11.0	3.8	3.78	3.9	51	86	-12	25.65	99.90	5
2021-05-21	20:56: 02	25.63	99.93	8.0	4.7	5.02	4.4	27	58	-45	25.62	99.93	6
2021-05-21	21:21: 25	25.63	99.92	10.0	5.9	5.76	5.7	312	78	-168	25.63	99.92	7
2021-05-21	21:21: 57	25.63	99.96	10.0	4.7	5.76	5.2	315	78	176	25.62	99.95	8
2021-05-21	21:22: 35	25.60	99.98	10.0	4.3	6.37	4.6	121	59	133	25.60	99.98	9
2021-05-21	21:48: 34	25.67	99.87	8.0	6.6	5.89	6.1	225	75	-3	25.68	99.87	10(主震)
2021-05-21	22:15: 16	25.59	99.96	8.0	4.5	6.40	4.4	134	88	160	25.59	99.97	11
2021-05-21	22:31: 10	25.59	99.97	8.0	5.6	8.16	5.1	46	77	-36	25.59	99.98	12
2021-05-21	22:59: 37	25.63	99.94	8.0	4.1	6.29	4.0	105	72	153	25.62	99.94	13
2021-05-21	23:13: 53	25.64	99.94	8.0	4.3	5.35	4.0	30	86	-1	25.61	99.94	14
2021-05-21	23:23: 34	25.60	99.98	8.0	4.9	4.30	4.5	216	81	7	25.59	99.98	15
2021-05-22	00:51: 41	25.70	99.87	8.0	4.5	3.60	4.3	34	82	-10	25.68	99.88	16
2021-05-22	01:50: 17	25.61	100.00	14.0	3.9	3.54	3.9	317	80	-174	25.60	99.96	17
2021-05-22	08:36: 46	25.68	99.90	12.0	4.0	5.20	3.9	16	62	-25	25.67	99.89	18
2021-05-22	09:48: 00	25.67	99.90	12.0	4.5	4.19	3.7	312	83	-176	25.66	99.88	19
2021-05-22	20:14: 36	25.61	99.93	10.0	4.8	6.90	4.3	318	49	-150	25.59	99.93	20
2021-05-22	22:30: 05	25.60	99.93	11.0	3.8	7.20	3.8	308	70	-166	25.58	99.92	21
2021-05-22	23:30: 16	25.57	99.96	12.0	3.5	7.40	3.6	137	54	-138	25.58	99.96	22
2021-05-23	00:17: 19	25.59	99.99	9.0	3.5	5.95	3.6	334	74	-150	25.56	99.96	23
2021-05-24	08:10: 58	25.59	100.00	8.0	3.6	6.64	3.6	141	80	170	25.55	100.00	24
2021-05-27	19:52: 46	25.74	99.95	12.0	4.1	6.07	4.35	285	82	175	25.73	99.93	25
2021-05-27	23:03: 57	25.69	99.89	12.0	3.6	7.13	4.0	144	75	-143	25.68	99.87	26

表3 云南漾濞M6.4地震序列的震源参数

Table3 Source parameters of Yangbi M6.4 earthquake sequence in Yunnan Province

日期	时间	北纬 /(°)	东经 /(°)	深度 /km	震级 M	矩心深度 /km	矩震级 M_W	走向 /(°)	倾角 /(°)	滑动角 /(°)	精定位后北纬 /(°)	精定位后东经 /(°)	序号
2021-05-18	20:56: 46	25.65	99.93	8.0	3.6	6.26	3.7	132	86	-163	25.62	99.93	1
2021-05-18	21:39: 35	25.65	99.93	8.0	4.7	5.35	4.4	308	82	162	25.63	99.93	2
2021-05-19	03:27: 56	25.65	99.92	8.0	3.7	4.95	3.8	314	80	172	25.63	99.92	3
2021-05-19	21:13: 07	25.68	99.89	8.0	3.8	4.79	4.0	312	83	179	25.66	99.89	4
2021-05-20	01:58: 59	25.67	99.90	11.0	3.8	3.78	3.9	51	86	-12	25.65	99.90	5
2021-05-21	20:56: 02	25.63	99.93	8.0	4.7	5.02	4.4	27	58	-45	25.62	99.93	6
2021-05-21	21:21: 25	25.63	99.92	10.0	5.9	5.76	5.7	312	78	-168	25.63	99.92	7
2021-05-21	21:21: 57	25.63	99.96	10.0	4.7	5.76	5.2	315	78	176	25.62	99.95	8
2021-05-21	21:22: 35	25.60	99.98	10.0	4.3	6.37	4.6	121	59	133	25.60	99.98	9
2021-05-21	21:48: 34	25.67	99.87	8.0	6.6	5.89	6.1	225	75	-3	25.68	99.87	10(主震)
2021-05-21	22:15: 16	25.59	99.96	8.0	4.5	6.40	4.4	134	88	160	25.59	99.97	11
2021-05-21	22:31: 10	25.59	99.97	8.0	5.6	8.16	5.1	46	77	-36	25.59	99.98	12
2021-05-21	22:59: 37	25.63	99.94	8.0	4.1	6.29	4.0	105	72	153	25.62	99.94	13
2021-05-21	23:13: 53	25.64	99.94	8.0	4.3	5.35	4.0	30	86	-1	25.61	99.94	14
2021-05-21	23:23: 34	25.60	99.98	8.0	4.9	4.30	4.5	216	81	7	25.59	99.98	15
2021-05-22	00:51: 41	25.70	99.87	8.0	4.5	3.60	4.3	34	82	-10	25.68	99.88	16
2021-05-22	01:50: 17	25.61	100.00	14.0	3.9	3.54	3.9	317	80	-174	25.60	99.96	17
2021-05-22	08:36: 46	25.68	99.90	12.0	4.0	5.20	3.9	16	62	-25	25.67	99.89	18
2021-05-22	09:48: 00	25.67	99.90	12.0	4.5	4.19	3.7	312	83	-176	25.66	99.88	19
2021-05-22	20:14: 36	25.61	99.93	10.0	4.8	6.90	4.3	318	49	-150	25.59	99.93	20
2021-05-22	22:30: 05	25.60	99.93	11.0	3.8	7.20	3.8	308	70	-166	25.58	99.92	21
2021-05-22	23:30: 16	25.57	99.96	12.0	3.5	7.40	3.6	137	54	-138	25.58	99.96	22
2021-05-23	00:17: 19	25.59	99.99	9.0	3.5	5.95	3.6	334	74	-150	25.56	99.96	23
2021-05-24	08:10: 58	25.59	100.00	8.0	3.6	6.64	3.6	141	80	170	25.55	100.00	24
2021-05-27	19:52: 46	25.74	99.95	12.0	4.1	6.07	4.35	285	82	175	25.73	99.93	25
2021-05-27	23:03: 57	25.69	99.89	12.0	3.6	7.13	4.0	144	75	-143	25.68	99.87	26

表4 震源机制解分类

Table4 Categories of focal mechanisms

类型	P轴倾俯角	B轴倾俯角	T轴倾俯角
正断型(NF)	≥52°		≤35°
正走滑型(NS)	40°≤倾角<52°		≤20°
走滑型(SS)	<40°	≥45°	≤20°
	≤20°	≥45°	<40°
逆走滑型(TS)	≤20°		40°≤倾角<52°
逆断型(TF)	≤35°		≥52°
不确定型(U)	上述类型之外的震源机制解

图8 2021年5月21云南漾濞M6.4地震序列的震源机制解红色震源球为主震, 蓝色震源球为前震及余震; 红色五角星为主震震中, 蓝色五角星为M≥3.6前震及余震震中; 不同颜色的圆点为余震。绿色圆形 M<2, 褐色圆形 2≤M<3, 橘黄色圆形 3≤M<4, 黄色圆形 4≤M<5, 蓝色圆形 5≤M<6

Fig. 8 Focal mechanisms of the May 21, 2021 Yangbi M6.4 earthquake sequence in Yunnan Province.

图9 漾濞地震序列节面走向(strike)、 P轴方位角(Paz)、 T轴方位角(Taz)、滑动角(rake)、P轴倾伏角(Ppl)、 T轴倾伏角(Tpl)的玫瑰花图

Fig. 9 Rose maps of the strike, Paz, Taz, rake, Ppl, Tpl, of the Yangbi earthquake sequences.

表5 不同分区反演得到的应力场参数

Table5 The inverted stress field parameters on grid of different regions

分区	σ₁轴		σ₂轴		σ₃轴		R值
	方位角/(°)	倾伏角/(°)	方位角/(°)	倾伏角/(°)	方位角/(°)	倾伏角/(°)
北西段	-7.12	13.43	-97.29	0.75	169.58	76.55	0.33
中段	-3.39	9.28	-93.49	0.60	172.85	80.70	0.29
南东段东支	-172.63	3.99	-96.38	13.82	-66.85	75.59	0.37
南东段西支	179.76	3.64	89.58	2.83	-38.18	85.39	0.14

图10 模型长度与数据拟合误差之间的折中曲线图空心圆圈旁所标数字为阻尼参数, “+”表示所选择的最佳阻尼系数

Fig. 10 Trade-off between model length and misfit calculated from the corresponding damping parameters.

图11 水平最大主应力SHmax反演结果扇形区域为95%置信区间, 应力状态分类采用WSM标准

Fig. 11 Maximum horizontal stress orientations(SHmax).

图12 应力场反演结果红点表示95%置信度下最大主压应力轴σ1的不确定范围, 绿点表示95%置信度下中间应力轴σ2的不确定范围, 蓝点表示95%置信度下最大主张应力轴σ3的不确定范围; 黑色实线加号表示最优解; 应力单元的背景颜色表示反演的应力形因子分布

Fig. 12 Stereomap of stress field inversion results.

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