青藏高原东北缘地震波衰减特征及地震震源参数研究

doi:10.3969/j.issn.0253-4967.2021.06.016

摘要/Abstract

摘要：

文中基于青藏高原东北缘2010—2019年中小地震三分量S波数据, 采用联合反演方法, 获得了研究区的地震波几何衰减模型、 Q值、区内444次地震的震源参数以及118个台站的场地响应结果。研究显示, 青藏高原东北缘几何衰减符合三段式分段函数形式, 在该几何衰减模型的基础上, 非弹性衰减模型满足Q(f)=401.8×f^0.2963; 在研究区内的118个台站中, 88个台站场地响应符合基岩场地特征, 20个台站场地响应存在一定的放大效应, 且多数台站的放大效应表现在高频段, 另有10个台站的场地响应计算结果整体略<1, 可能受到速度结构和Q值空间各向异性的影响。通过地方震级、矩震级、应力降和视应力的相关性研究, 发现矩震级与地方震级整体呈线性相关, 在矩震级相同的情况下, 地方震级与地震应力降和视应力整体呈正相关。应力降和视应力间存在较为显著的统计相关性, 在对数坐标系下呈明显的线性相关关系。在矩震级相同的情况下, 地方震级较低的地震视应力与应力降的比值较高, 表明地震破裂较充分, 地震波辐射能相对较小; 地方震级较高的地震视应力与应力降的比值较低, 表明断层破裂过程中损耗的能量较小, 地震波辐射能相对较高。

关键词: 青藏高原东北缘, Q值, 应力降, 视应力衰减模型

Abstract:

The northeastern margin of the Qinghai-Tibet Plateau located near the middle and northern section of the north-south seismic belt in China is a place where historical seismicity is extremely high and many strong earthquakes of magnitude above 7 occurred, including the August 8^th 2017 M7.0 Jiuzhaigou earthquake and the May 22^th 2021 M7.4 Maduo earthquake. There are many active faults in this region, most of them are NWW trending, among which the Maqin-Maqu segment on the east verge of the East Kunlun Fault is especially dangerous because a seismic gap exists on it. The 2017 M7.0 Jiuzhaigou earthquake and the 2021 M7.4 Maduo earthquake which occurred near the seismic gap are still not able to remove the danger of a future strong earthquake along the Maqin-Maqu segment. The seismic activity of a certain region is closely related to the variation of regional stress field and the physical properties of underground medium. With the development of the broadband digital seismic networks, source parameters, attenuation characteristics of seismic waves and site responses can be deduced from three-component seismic signals of regional small and medium earthquakes. Study results on the current state of regional stress and underground medium properties can provide basic information for the establishment of strong ground motion attenuation model and the assessment of seismic hazard in the study area.
In this study, the geometric attenuation model, Q value, source parameters of 444 earthquakes and the site responses of 118 stations are obtained near the northeast margin of Qinghai-Tibet Plateau using the joint inversion method based on the three-component S-wave data of small and medium-sized earthquakes occurring during 2010 to 2019. The results shows that the geometric attenuation model in the study area conforms to a form of 3-segment piecewise function, while the inelastic attenuation model meets Q(f)=401.8×f^0.2963 based on this geometric attenuation model. Among the site responses of 118 stations, 88 site responses show characteristics of rock site, 20 site responses show amplification effect, particularly in the high frequency, and 10 site responses show the overall value below 1, which may be affected by the spatial anisotropy of velocity structure and Q value. Through the correlation study of local magnitude, moment magnitude, stress drop and apparent stress, it is found that the moment magnitude has a linear correlation with the local magnitude as a whole, and the local magnitude has a positive correlation with the earthquake stress drop and apparent stress under the same moment magnitude. There is a significant statistical correlation between stress drop and apparent stress and an obvious linear correlation in logarithmic coordinate system. Under the same moment magnitude, the ratio of the apparent stress to the stress drop is higher in the earthquake with lower local magnitude, which means the seismic rupture is more sufficient and the radiation energy is relatively small. While the ratio of apparent stress to stress drop is relatively low in the earthquake with higher local magnitude, indicating the energy loss during fault rupture is relatively small and the radiation energy is relatively high.

Key words: the northeast margin of Qinghai-Tibet Plateau, Q value, stress drop, apparent stress, attenuation model

中图分类号:

P315.2

臧阳, 俞言祥, 孟令媛, 韩颜颜. 青藏高原东北缘地震波衰减特征及地震震源参数研究[J]. 地震地质, 2021, 43(6): 1638-1656.

ZANG Yang, YU Yan-xiang, MENG Ling-yuan, HAN Yan-yan. STUDY ON ATTENUATION CHARACTERISTICS OF SEISMIC WAVES AND SEISMIC SOURCE PARAMETERS IN THE NORTH-EAST MARGIN OF QINGHAI-TIBET PLATEAU[J]. SEISMOLOGY AND EGOLOGY, 2021, 43(6): 1638-1656.

图/表 10

图 1 参与反演计算的地震、台站和射线路径分布图

Fig. 1 Earthquakes, seismic stations and ray paths distribution involved in the inversion calculation.

图 2 不同台站记录到的2011年2月24日青海兴海ML4.1地震T分量S波记录、去噪声后的观测位移谱及联合反演得到的地震震源位移谱 a 青海兴海台(QH.XIH)S波T分量记录及观测位移谱; b 青海大武台(QH.DAW)S波T分量记录及观测位移谱; c 青海都兰台(QH.DUL)S波T分量记录及观测位移谱; d 青海湟源台(QH.HUY)S波T分量记录及观测位移谱; e 青海德令哈台 (QH.DLH)S波T分量记录及观测位移谱; f 联合反演得到的青海兴海ML4.1地震的震源位移谱

Fig. 2 The T-component S-wave records, observed noise-removed displacement spectra of the ML4.1 Xinghai earthquake on February 24, 2011 recorded by different stations and the source displacement spectra obtained by joint inversion.

图 3 几何衰减模型理论值及归一化振幅谱实测值 a 采用线性的几何衰减模型; b 采用二段式分段函数的几何衰减模型; c 采用三段式分段函数的几何衰减模型

Fig. 3 Theoretical values of geometric attenuation model and measured values of normalized amplitude spectrum.

图 4 Q值及对数坐标下的线性拟合计算结果 a 采用线性的几何衰减模型; b 采用二段式分段函数的几何衰减模型; c 采用三段式分段函数的几何衰减模型

Fig. 4 Q value and the result of linear fitting in logarithmic coordinates.

图 5 各区域Q值随频率f变化的曲线对比图

Fig. 5 The comparison of the variation curve of Q with frequency f in different regions.

图 6 反演得到的研究区不同台站的场地响应函数S(f) a 具有典型基岩场地特征的场地响应; b 具有一定放大效应的场地响应; c 计算结果整体略<1的场地响应

Fig. 6 Site response function of different stations in the study area obtained by inversion.

图 7 具有不同场地响应特征的台站分布图

Fig. 7 Station distribution map with different site response characteristics.

表1 ML≥4.0地震的震源参数反演结果

Table1 Seismic source parameters of ML≥4.0 events

序号	地震时间	震级 /M_L	矩震级 /M_W	破裂半径 /km	应力降Δσ /bar	视应力σ_app /bar
1	2010-08-25	4.1	3.33	0.35	11.36	5.19
2	2011-02-23	4.7	3.67	1.44	0.52	1.22
3	2011-02-24	4.1	3.28	0.45	4.47	2.70
4	2011-02-24	4.5	3.43	0.49	5.66	3.77
5	2011-03-03	4.5	3.60	1.46	0.39	0.83
6	2011-05-02	4.8	4.02	2.37	0.39	0.85
7	2011-06-10	4.4	3.65	1.62	0.34	0.83
8	2011-09-26	4.0	3.34	0.61	2.16	1.98
9	2011-11-02	4.9	3.90	0.99	3.54	4.97
10	2012-04-05	4.2	3.20	0.49	2.70	1.91
11	2012-06-03	4.2	3.46	0.94	0.91	2.64
12	2012-08-27	4.3	3.48	0.84	1.38	1.76
13	2013-05-08	4.3	3.47	0.62	3.34	3.56
14	2013-07-22	4.0	3.89	3.30	0.09	0.35
15	2013-07-22	4.3	3.59	0.79	2.44	3.04
16	2013-07-22	4.2	3.32	0.89	0.66	1.13
17	2013-07-27	4.9	4.02	1.21	2.95	5.75
18	2013-07-28	4.6	3.53	0.84	1.61	2.08
19	2013-08-17	4.1	3.43	0.96	0.76	1.17
20	2013-10-20	4.5	3.51	0.77	2.01	2.51
21	2014-03-13	4.2	3.40	0.84	1.05	1.33
22	2014-08-11	4.7	3.81	1.85	0.40	0.99
23	2014-11-21	4.8	3.88	1.79	0.56	1.53
24	2014-11-22	4.8	3.92	1.48	1.15	1.98
25	2014-12-02	4.2	3.34	0.44	5.73	4.18
26	2014-12-22	4.0	3.26	0.59	1.88	2.16
27	2015-02-04	4.5	3.62	1.57	0.34	0.75
28	2015-03-20	4.1	3.36	0.44	6.14	3.88
29	2015-04-10	4.3	3.39	0.47	5.64	3.78
30	2015-04-15	4.9	3.99	1.07	3.87	7.07
31	2015-12-18	4.2	3.45	0.81	1.40	1.92
32	2016-01-18	4.5	3.54	0.72	2.66	2.74
33	2016-03-21	4.6	3.84	0.84	4.78	5.74
34	2016-05-07	4.4	3.57	0.80	2.21	2.49
35	2017-05-16	4.8	3.87	1.81	0.53	1.07
36	2017-08-09	4.0	3.40	1.08	0.48	0.83
37	2017-08-09	4.2	3.68	1.55	0.44	1.06
38	2017-08-09	4.3	3.69	1.48	0.52	1.14
39	2017-08-09	4.4	3.80	1.26	1.21	2.19
40	2017-08-09	4.2	3.67	1.36	0.64	1.16
41	2017-08-09	4.3	3.52	0.96	1.07	1.56
42	2017-08-09	5.2	4.12	1.72	1.47	3.11
43	2017-08-10	4.1	3.61	1.48	0.40	0.88
44	2017-08-10	4.8	3.95	1.56	1.09	2.18
45	2017-08-10	4.0	3.38	0.93	0.72	0.96
46	2017-08-10	4.6	3.75	1.21	1.17	1.93
47	2017-08-11	4.0	3.36	0.86	0.87	1.01
48	2017-08-12	4.2	3.48	1.06	0.69	1.06
49	2017-08-13	4.0	3.29	0.77	0.92	1.05
50	2017-10-06	4.5	3.54	0.83	1.75	2.10
51	2017-10-15	4.0	3.27	0.51	3.05	2.16
52	2017-10-17	4.0	3.47	0.90	1.07	1.55
53	2017-10-31	4.8	3.79	1.09	1.85	2.94
54	2017-11-03	4.3	3.47	1.24	0.41	0.87
55	2017-11-07	5.1	4.17	2.16	0.88	2.24
56	2017-11-19	4.0	3.46	1.00	0.74	1.32
57	2017-12-15	5.3	4.35	1.94	2.24	5.71
58	2017-12-15	4.4	3.80	1.33	1.05	2.19
59	2018-07-22	4.0	3.36	0.89	0.77	1.21
60	2019-03-14	4.7	3.83	0.91	3.63	4.76
61	2019-10-28	5.9	4.60	1.97	5.07	11.32
62	2019-11-17	4.1	3.42	0.73	1.70	1.90

表1 ML≥4.0地震的震源参数反演结果

Table1 Seismic source parameters of ML≥4.0 events

序号	地震时间	震级 /M_L	矩震级 /M_W	破裂半径 /km	应力降Δσ /bar	视应力σ_app /bar
1	2010-08-25	4.1	3.33	0.35	11.36	5.19
2	2011-02-23	4.7	3.67	1.44	0.52	1.22
3	2011-02-24	4.1	3.28	0.45	4.47	2.70
4	2011-02-24	4.5	3.43	0.49	5.66	3.77
5	2011-03-03	4.5	3.60	1.46	0.39	0.83
6	2011-05-02	4.8	4.02	2.37	0.39	0.85
7	2011-06-10	4.4	3.65	1.62	0.34	0.83
8	2011-09-26	4.0	3.34	0.61	2.16	1.98
9	2011-11-02	4.9	3.90	0.99	3.54	4.97
10	2012-04-05	4.2	3.20	0.49	2.70	1.91
11	2012-06-03	4.2	3.46	0.94	0.91	2.64
12	2012-08-27	4.3	3.48	0.84	1.38	1.76
13	2013-05-08	4.3	3.47	0.62	3.34	3.56
14	2013-07-22	4.0	3.89	3.30	0.09	0.35
15	2013-07-22	4.3	3.59	0.79	2.44	3.04
16	2013-07-22	4.2	3.32	0.89	0.66	1.13
17	2013-07-27	4.9	4.02	1.21	2.95	5.75
18	2013-07-28	4.6	3.53	0.84	1.61	2.08
19	2013-08-17	4.1	3.43	0.96	0.76	1.17
20	2013-10-20	4.5	3.51	0.77	2.01	2.51
21	2014-03-13	4.2	3.40	0.84	1.05	1.33
22	2014-08-11	4.7	3.81	1.85	0.40	0.99
23	2014-11-21	4.8	3.88	1.79	0.56	1.53
24	2014-11-22	4.8	3.92	1.48	1.15	1.98
25	2014-12-02	4.2	3.34	0.44	5.73	4.18
26	2014-12-22	4.0	3.26	0.59	1.88	2.16
27	2015-02-04	4.5	3.62	1.57	0.34	0.75
28	2015-03-20	4.1	3.36	0.44	6.14	3.88
29	2015-04-10	4.3	3.39	0.47	5.64	3.78
30	2015-04-15	4.9	3.99	1.07	3.87	7.07
31	2015-12-18	4.2	3.45	0.81	1.40	1.92
32	2016-01-18	4.5	3.54	0.72	2.66	2.74
33	2016-03-21	4.6	3.84	0.84	4.78	5.74
34	2016-05-07	4.4	3.57	0.80	2.21	2.49
35	2017-05-16	4.8	3.87	1.81	0.53	1.07
36	2017-08-09	4.0	3.40	1.08	0.48	0.83
37	2017-08-09	4.2	3.68	1.55	0.44	1.06
38	2017-08-09	4.3	3.69	1.48	0.52	1.14
39	2017-08-09	4.4	3.80	1.26	1.21	2.19
40	2017-08-09	4.2	3.67	1.36	0.64	1.16
41	2017-08-09	4.3	3.52	0.96	1.07	1.56
42	2017-08-09	5.2	4.12	1.72	1.47	3.11
43	2017-08-10	4.1	3.61	1.48	0.40	0.88
44	2017-08-10	4.8	3.95	1.56	1.09	2.18
45	2017-08-10	4.0	3.38	0.93	0.72	0.96
46	2017-08-10	4.6	3.75	1.21	1.17	1.93
47	2017-08-11	4.0	3.36	0.86	0.87	1.01
48	2017-08-12	4.2	3.48	1.06	0.69	1.06
49	2017-08-13	4.0	3.29	0.77	0.92	1.05
50	2017-10-06	4.5	3.54	0.83	1.75	2.10
51	2017-10-15	4.0	3.27	0.51	3.05	2.16
52	2017-10-17	4.0	3.47	0.90	1.07	1.55
53	2017-10-31	4.8	3.79	1.09	1.85	2.94
54	2017-11-03	4.3	3.47	1.24	0.41	0.87
55	2017-11-07	5.1	4.17	2.16	0.88	2.24
56	2017-11-19	4.0	3.46	1.00	0.74	1.32
57	2017-12-15	5.3	4.35	1.94	2.24	5.71
58	2017-12-15	4.4	3.80	1.33	1.05	2.19
59	2018-07-22	4.0	3.36	0.89	0.77	1.21
60	2019-03-14	4.7	3.83	0.91	3.63	4.76
61	2019-10-28	5.9	4.60	1.97	5.07	11.32
62	2019-11-17	4.1	3.42	0.73	1.70	1.90

图 8 MW2.5~4.7地震的震源参数与地震矩震级相关性 a 应力降计算结果; b 视应力计算结果

Fig. 8 Correlation between seismic source parameters and moment magnitudes in the range of MW2.5 ~4.7.

图 9 地方震级(ML)、矩震级(MW)、应力降(Δσ)、视应力(σapp)的相关关系 a 地方震级与矩震级的相关性; b 矩震级与应力降的相关性; c 矩震级与视应力的相关性; d 视应力与应力降的相关性。图a中黑色空心正方形为拟合值1倍标准差内的地震, 浅红色正方形为拟合值加1~1.96倍均方差内的地震, 深红色正方形为超过拟合值加1.96倍均方差的地震, 浅蓝色正方形为拟合值减1~1.96倍均方差内的地震, 深蓝色正方形为低于拟合值减1.96倍均方差的地震, 图b、 c、 d中圆的颜色含义与图a一致; 图b、 c灰色方框为间隔0.5矩震级范围数据在对数坐标下的平均值, 误差棒为对数坐标下平均值的1倍均方差范围

Fig. 9 Correlation between local magnitude(ML), moment magnitude(MW),stress drop(Δσ)and apparent stress(σapp).

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