2023年平原MS5.5地震矩张量反演及发震构造

doi:10.3969/j.issn.0253-4967.2025.01.017

摘要/Abstract

摘要： 2023年8月6日山东省德州市平原县发生 M_S5.5 地震, 震中周边河北、河南、天津及北京等多地震感明显, 该地震打破了震中50km范围内无M≥5.0地震的历史记录, 并引起了社会和地震工作者的广泛关注。基于震中周边的区域地震台网地震资料, 文中采用gCAP方法反演了平原 M_S5.5 地震的矩张量解, 利用双差定位方法对平原 M_S5.5 地震序列中M_L≥1.0的地震进行了重定位, 基于震源机制与区域应力场的数值关系模拟方法计算了平原 M_S5.5 地震震源机制节面的相对剪应力和正应力, 根据重定位结果拟合了断层面, 并分析了该平原地震序列的发震构造。结果显示: 1)平原 M_S5.5 地震的地震矩(M₀)为1.97Í10¹⁷N·m、矩震级为 M_W5.5, 矩心深度16km, 矩张量解M_rr、M_tt、M_pp、M_rt、M_rp、M_tp分别为-0.129、1.194、-0.459、0.009、0.336、0.245, 其最佳双力偶(DC)、各向同性(ISO)、补偿线性向量偶极(CLVD)成分占全矩张量解的92.40%、6.25%、1.35%, 最佳双力偶解的节面Ⅰ的走向、倾角、滑动角分别为222°、71°、-156°, 节面Ⅱ的走向、倾角、滑动角为124°、67°、-21°, P轴方位84°、倾伏角为30°, 显示该地震为走滑型天然地震事件且略带少量的正断分量, 震源区主压应力呈现近NEE-SWW向的推挤特征, 这与华北平原的区域应力场主压应力方向基本一致。2)重定位后的平原 M_S5.5 地震序列震中主要呈NE-SW向优势展布, 长约15km、宽约5km, M_L≥1.0地震的震源深度主要集中在8~22km之间, 平均深度为15.4km, 震源深度剖面显示可能的发震构造倾向NW。3)现今应力场与震源机制数值关系模拟显示, 平原地区的应力体系在平原 M_S5.5 地震震源机制节面Ⅰ和节面Ⅱ产生的相对剪应力分别为0.860和0.689。断层面拟合揭示平原地震发震断层具有右旋走滑的运动性质。4)结合已有研究分析认为, 平原 M_S5.5 地震的震源机制节面Ⅰ为其可能的发震破裂面, 主震发震断层倾角为71°, 地震序列主要发震构造为走向SW、倾向NW的高倾角隐伏断层, 平原 M_S5.5 地震是由于华北平原NEE-SWW向区域应力场主压应力的作用下, 应力得到了充分积累, 在剪应力的最优释放节面破裂引起的一次略具正断分量的右旋走滑型地震事件。

关键词: 平原M_S5.5地震, 矩张量反演, 重定位, 相对剪应力, 发震构造

Abstract:

On August 6, 2023, an earthquake with M_S5.5 occurred in Pingyuan County, Dezhou City, in Shandong Province, North China. Around the epicenter of the M_S5.5 Pingyuan earthquake, obvious earthquake tremors were felt through the regions of Hebei, Henan, Tianjin, Beijing etc. This earthquake also broke the historical record of no earthquake with M≥5.0 within 50km of the epicenter and aroused widespread concern of the society and seismologists. It is urgent to carry out the research on strong earthquake seismogenic structures and seismogenic environments in the basin, which is of great significance to strengthen the seismic tectonic environment exploration and earthquake damage prevention in the weak and rare earthquake areas of the North China Plain. Based on the data of the Regional Seismic Networks around the epicenter, moment tensor solution and centroid depth of the M_S5.5 Pingyuan earthquake were determined using the gCAP inversion method, and the stability of moment tensor inversion of the mainshock is evaluated by Bootstrap method. The M_L≥1.0 earthquakes of the M_S5.5 Pingyuan earthquake sequence were relocated using the double-difference relocation method. By simulation method of the relationship between regional stress regime and focal mechanism, the relative shear stress and normal stress of nodal planes from focal mechanism of the M_S5.5 Pingyuan earthquake were obtained. According to the earthquake relocation, the fault plane was fitted, and the seismogenic structure of the earthquake was analyzed. The results indicate: 1)The scalar seismic moment(M₀)of the M_S5.5 Pingyuan earthquake is 1.97Í10¹⁷N·m, while the moment magnitude is M_W5.5, and the centroid depth is 16km. The moment tensor solution(M_rr/M_tt/M_pp/M_rt/M_rp/M_tp)is -0.129/1.194/-0.459/0.009/0.336/0.245, while the double-couple(DC), isotropic(ISO) and compensated linear vector dipole(CLVD) components account for 92.40%, 6.25%, and 1.35% of the full moment tensor solution. The focal mechanism of the double-couple solution shows that the M_S5.5 Pingyuan earthquake is a strike-slip type natural earthquake event with a little normal fault component, with strike/dip/rake of 222°/71°/-156° and 124°/67°/-21° for nodal planes Ⅰ and Ⅱ. The P-axis azimuth is 84° with plunge angle of 30°, indicating the principal compressive stress in the NEE direction in the focal area, basically consistent with the direction of the main compressive stress of the regional tectonic stress in the North China Plain. The best double-couple solutions of focal mechanism obtained by the Bootstrap method are: strike 220.4°±2.49°, dip 71.5°±4.34°, rake -155.9°±3.58° for the nodal plane Ⅰ, and strike 122.2°±2.83°, dip 67.3°±3.17°, rake -20.2°±4.95° for nodal plane Ⅱ, and centroid depth 16.7±1.10km, reflecting the stability and reliability of moment tensor inversion in this paper. 2)After earthquake relocation, the epicenters of the M_S5.5 Pingyuan earthquake sequence mainly show a dominant distribution in the NE-SW direction, with a length of about 15km and a width of about 5km. The epicenter of the M_S5.5 Pingyuan earthquake is located in the southwest segment of the earthquake sequence, and the epicenters of the M_L≥1.0 earthquake are relatively concentrated on the NE side of the main earthquake, while the distribution of the epicenters of the SW side is relatively sparse. The focal depths of earthquakes with M_L≥1.0 are mainly between 8 and 22km, with an average depth of 15.4km. The focal depth profiles demonstrate the fault plane with a dip to the northwest. 3)The regional stress field of North China Craton primarily exhibits NEE-SWW compression and near N-S tensile. The main stress axis direction of the regional stress field is basically consistent with the P-axis of the focal mechanism of the M_S5.5 Pingyuan earthquake. The strike-slip component of the focal mechanism of the M_S5.5 Pingyuan earthquake shows general consistency with the focal mechanism characteristics of the eastern North China Craton. It is also consistent with the E-W compressive and S-N tensile tectonic stress background of the eastern part of the North China Craton, and the small normal components may be related to the tensile movement of the central and western region of Bohai Bay Basin. The relationship between the focal mechanism and contemporary regional stress regime shows the relative shear stress of 0.860/0.689 for nodal planes I and II under the stress field of the Pingyuan region, and the rake of shear stress for the nodal plane I is close to the rake of focal mechanism. The shear stress on nodal plane I of the focal mechanism is relatively high, reflecting that nodal plane I is very close to the fault shape of the optimal release of relative shear stress of the regional stress field, presenting the source property of right-lateral strike-slip with a small amount of normal component. The fault plane fitting also exhibits the mode of fault movement with right-lateral strike-slip. 4)Combined with the previous studies, it is inferred that the nodal plane I of the focal mechanism for the M_S5.5 Pingyuan mainshock is the possible seismic source fault with a dip angle of 71°, and the main seismogenic structure of the Pingyuan earthquake sequence may be a SW-striking blind fault with steep dip to northwest. Under the long-term contemporary principal compressive stress of the tectonic stress field in North China Plain, the M_S5.5 Pingyuan earthquake occurred as a right-lateral strike-slip seismic dislocation with a little normal fault component due to the rupture on the nodal plane with optimum shear stress release. It is suggested that the seismogenic structure of the Pingyuan earthquake may be related to the Lingxian-Guanxian fault, a hidden fault system formed by the northern section of the Guanxian fault and the southern section of the Lingxian-Yangxin fault.

Key words: M_S5.5 Pingyuan earthquake, moment tensor inversion, earthquake relocation, relative shear stress, seismogenic structure

许英才, 郭祥云. 2023年平原M_S5.5地震矩张量反演及发震构造[J]. 地震地质, 2025, 47(1): 284-305.

XU Ying-cai, GUO Xiang-yun. MOMENT TENSOR INVERSION AND SEISMOGENIC STRUCTURE OF THE 2023 M_S5.5 PINGYUAN EARTHQUAKE[J]. SEISMOLOGY AND GEOLOGY, 2025, 47(1): 284-305.

图/表 17

图1 平原 MS5.5 地震震中周边区域的地质构造及历史地震(MS≥5.0)分布黑色线条为研究区断层(邓起东等, 2007), 红色三角形为参与矩张量反演的台站, 虚圆圈由内到外为震中距50km、100km、200km和300km的范围

Fig. 1 The tectonics and historical earthquakes with MS≥5.0 around the epicenter of the MS5.5 Pingyuan earthquake.

图2 平原 MS5.5 地震序列的M-T和日频次图

Fig. 2 M-T and daily frequency diagram of the MS5.5 Pingyuan earthquake sequence.

表1 平原地区一维速度模型

Table 1 1-D velocity model for the Pingyuan region

层号	1	2	3	4	5	6	7
顶层深度H/km	0	5	10	15	20	25	35
V_P/km·s^-1	4.86	5.55	5.68	6.02	6.35	6.95	7.67
波速比k	1.71

图3 平原 MS5.5 地震矩张量反演残差随深度变化

Fig. 3 Variation of fitting error with depth during the moment tensor inversion of the MS5.5 Pingyuan earthquake.

图4 平原 MS5.5 地震矩张量解最佳拟合深度的观测波形(黑)与理论波形(红)拟合图波形左侧字母为台站名, 台站右侧数字为方位角(单位: 度), 其下方分别为震中距(单位: km)和相对偏移时间(单位: s); 波形下方的数字为观测波形相对于理论波形的移动时间(单位: s)和二者的相关系数(单位: %)

Fig. 4 Comparison between the observed(black)and synthetic(red)waveforms at the best fitting depth of the MS5.5 Pingyuan earthquake.

图5 通过 1 000次Bootstrap方法反演得到的平原 MS5.5 地震震源机制解结果 var 标准差; ave 均值; ζ ISO分量; χ CLVD分量

Fig. 5 Focal mechanism solutions of the MS5.5 Pingyuan earthquake by Bootstrap method in 1 000 times.

表2 平原 MS5.5 地震全矩张量解各分量的情况

Table 2 Components of the full moment tensor solution from the MS5.5 Pingyuan earthquake

2023年8月6日平原M_S5.5地震	ζ	χ	Λ^DC/%	Λ^CLVD/%	Λ^ISO/%
本文结果1(18个波形最佳台站)	0.25	-0.12	92.40	1.35	6.25
本文结果2(Bootstrap平均解)	0.24	-0.13	92.65	1.59	5.76

图6 平原 MS5.5 地震不同来源的震源机制结果的对比各个震源机制上方标示了其来源, 其下方为震源机制中心解相对于该震源机制结果的最小旋转角(单位: 度)

Fig. 6 Comparison of focal mechanism of the MS5.5 Pingyuan earthquake from different sources.

表3 平原 MS5.5 地震各种来源的震源机制解节面、P、T、B轴参数

Table 3 The nodal planes, P, T and B axes parameters of focal mechanisms of the MS5.5 Pingyuan earthquake from different sources

来源	节面Ⅰ/(°)			节面Ⅱ/(°)			P轴/(°)		T轴/(°)		B轴/(°)		最小旋转角 /(°)
来源	走向	倾角	滑动角	走向	倾角	滑动角	方位角	倾伏角	方位角	倾伏角	方位角	倾伏角
本文结果1	222	71	-156	124	67	-21	84	30	352	2	258	60	1.41
本文结果2	220	72	-156	122	67	-20	82	29	350	3	255	60	2.16
张喆等	224	72	-161	128	72	-19	86	26	356	0	266	64	5.25
地球所	220	67	-156	120	68	-25	80	33	170	1	261	57	5.66
NEIC	224	66	-154	123	66	-26	83	35	173	0	264	55	6.60
CENC	225	69	-150	123	62	-24	86	36	353	4	257	54	7.37
预测所	226	75	-149	127	60	-17	90	32	354	10	249	56	8.38
韩立波等	221	71	-148	120	60	-22	83	36	348	7	249	53	8.94
GFZ	220	76	-166	127	76	-14	83	20	173	0	264	70	9.51
郭祥云等	232	71	-153	133	65	-21	94	32	1	4	265	57	9.85
CPPT	209	86	-174	119	84	-4	74	7	344	1	243	83	23.78

图7 平原 MS5.5 地震的震源机制与区域应力场关系的数值模拟

Fig. 7 Simulation on the relationship between regional stress regime and focal mechanism of the MS5.5 Pingyuan earthquake.

图8 平原 MS5.5 地震震源机制2个节面的相对剪应力、P轴、区域主压应力及节面错动方式示意图

Fig. 8 Relative shear stress, P-axis, regional principal compressive stress and dislocation mode of two nodal planes from focal mechanism forthe MS5.5 Pingyuan earthquake.

表4 平原 MS5.5 地震震源机制解2个节面上的相对剪应力及正应力

Table 4 Relative shear stress and normal stress on the two nodal planes of the focal mechanism solution of the MS5.5 Pingyuan earthquake

平原M_S5.5地震的震源机制	相对剪应力	相对正应力	剪应力的滑动角/(°)	震源机制的滑动角/(°)	剪应力滑动角方向与震源机制滑动角方向之间的夹角/(°)
节面Ⅰ	0.860	0.543	164.4	-156	39.6
节面Ⅱ	0.689	-0.293	-3.7	-21	17.3

图9 重定位后的平原 MS5.5 地震序列震中分布 LNF 林南断裂; LX-YXF 陵县-阳信断裂。下文同

Fig. 9 Relocated epicenters of the MS5.5 Pingyuan earthquake sequence.

图10 平原 MS5.5 地震序列的AA'及BB'垂直剖面图

Fig. 10 Cross-sections of AA' and BB' for the MS5.5 Pingyuan earthquake sequence.

图11 平原 MS5.5 地震序列断层面拟合 a 震中分布图内矩形为参与断层面拟合的地震; b AA'剖面的地震投影; c 垂直于断层面横截面的投影; d 地震到断层面的距离分布(DD为沿倾向的距离, SD为沿走向的距离, D为震源深度, F为地震频次, DF为与断层的距离)

Fig. 11 Fault plane fitting of the MS5.5 Pingyuan earthquake sequence.

表5 根据重定位后平原地震序列拟合的断层面参数

Table 5 Parameters of the fitting fault from the relocated Pingyuan earthquake sequence

地震序列拟合断层面或主震震源机制节面	走向/(°)	倾角/(°)	滑动角/(°)	运动性质
平原M_S5.5地震序列重定位结果拟合的断层面	248	75	-139	右旋走滑兼正断
平原M_S5.5地震震源机制节面Ⅰ	222	71	-156	右旋走滑
平原M_S5.5地震震源机制节面Ⅱ	124	67	-21	左旋走滑

图12 平原 MS5.5 地震的发震构造 a 重定位后平原震中周缘断裂及地质构造; b 重定位后的震中分布、区域主压应力方向及断层错动方式平面图; c FF'地震剖面投影及震源机制垂直剖面投影; d 平原 MS5.5 地震发震断层的三维示意图

Fig. 12 Seismogenic structure of the MS5.5 Pingyuan earthquake.

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