川滇地区的震源机制解及应力场特征

doi:10.3969/j.issn.0253-4967.2022.01.011

摘要/Abstract

摘要：

基于川滇地区2000年1月—2017年3月2 600次M_L≥3.0地震的震源机制解, 文中对震源机制相对密集的次级地块和断裂带进行了震源机制量化分类和整体应力场反演, 利用1970年1月—2017年3月727次M_L≥4.0地震震源机制解, 采用区域应力张量阻尼方法反演了汶川8.0级和芦山7.0级强震前后川滇地区的主压应力空间分布, 探讨了川滇地区现今应力场的时空演化特征。川滇地区的震源机制总体以走滑型为主, 但龙门山断裂带、四川盆地及其边缘的马边-盐津断裂带的机制类型存在局部差异; 川滇地区的应力场存在明显的分区特征, 自北向南总体呈现顺时针旋转, 四川地区的主压应力方向从西到东经历了EW—NW—EW的转变, 云南地区的主压应力方向在西部地区呈NNE向, 在东部地区则表现为NNW向, 空间上形成倒“V”形; 汶川8.0级和芦山7.0级强震前后, 应力场在龙门山断裂带变化较大, 四川盆地及其周缘变化次之, 其他区域未发生明显变化, 其中震中所在的龙门山断裂带应力场经历了基本应力场—变化应力场—基本应力场的一次完整转变过程。

关键词: 川滇地区, 震源机制解, 区域应力场, 阻尼反演

Abstract:

Based on the focal mechanism solutions of 2 600 M_L≥3.0 earthquakes in Sichuan and Yunnan area from January 2000 to March 2017, the focal mechanism quantitative classification and stress field inversion are carried out for the sub blocks and fault zones with relatively dense focal mechanisms. Using the focal mechanism solutions of 727 M_L≥4.0 earthquakes from January 1970 to March 2017, the regional stress tensor damping method is used to inverse the spatial distribution of principal compressive stress in Sichuan and Yunnan area before and after Wenchuan M_S8.0 and Lushan M_S7.0 earthquakes, and the temporal and spatial evolution characteristics of current stress field are discussed.
The focal mechanisms are distributed mainly in Longmenshan fault zone, Xianshuihe-Anninghe-Zemuhe-Xiaojiang fault zone, Mabian-Yanjin fault zone, Lijiang-Xiaojinhe fault zone, the central Yunnan block, the west Yunnan block and the southwest Yunnan block in Sichuan and Yunnan area. The focal mechanism is mainly strike slip type in Sichuan and Yunnan area, but there are local differences. The Longmenshan fault zone is dominated by thrust type earthquakes, while in the Mabian-Yanjin fault zone, there are relatively more strike slip and thrust type earthquakes. The types of earthquakes in Sichuan Basin are complex, and there is no obvious dominant type. In general, the focal mechanisms of the Longmenshan fault zone and Sichuan Basin earthquakes are affected by strong earthquake and other factors, and the focal mechanism types have good inheritance in Sichuan and Yunnan area.
The stress field in Sichuan and Yunnan area has obvious subarea characteristics, and it rotates clockwise from north to south. The compressive stress in Longmenshan fault zone and Sichuan Basin shows nearly EW direction. It shows NWW direction in the eastern boundary of Sichuan and Yunnan rhombic block and NNW direction in the inner part of rhombic, while it shows NNE direction in the western and southern Yunnan blocks. The principal compressive stress in Sichuan is more complex than that in Yunnan. The principal compressive stress direction in Sichuan experiences EW-NW-EW rotation from west to east, the dip angle is steep in the west and slow in the east, and the stress regime also experiences the transition from normal faulting to strike-slip to thrust. The principal compressive stress direction in Yunnan is NNE in the west and NNW in the east, forming an inverted “V” shape in space, the stress regime is mainly strike-slip and the dip angle is horizontal.
Before and after the Wenchuan M_S8.0 and Lushan M_S7.0 strong earthquakes, the stress field in the Longmenshan fault zone changed greatly, followed by the Sichuan Basin and its surrounding areas, and there was no obvious change in other areas of Sichuan and Yunnan. The stress field in the Longmenshan fault zone experienced a complete transformation process from basic stress field to variable stress field to basic stress field.

Key words: Sichuan and Yunnan area, focal mechanism solution, regional stress field, damped inversion

中图分类号:

P315.2

张致伟, 龙锋, 赵小艳, 王迪. 川滇地区的震源机制解及应力场特征[J]. 地震地质, 2022, 44(1): 170-187.

ZHANG Zhi-wei, LONG Feng, ZHAO Xiao-yan, WANG Di. STUDY ON FOCAL MECHANISM SOLUTION AND STRESS FIELD CHARACTERISTICS IN SICHUAN AND YUNNAN AREA[J]. SEISMOLOGY AND GEOLOGY, 2022, 44(1): 170-187.

图/表 8

图 1 1900年以来青藏高原M≥7.0地震(a)及川滇地区活动地块与断裂带分布(b) Ⅰ 马尔康地块; Ⅱ 华南地块(四川盆地); Ⅲ 羌塘地块; Ⅳ 川滇菱形地块; Ⅳ1川西北地块; Ⅳ2滇中地块; Ⅴ 滇西地块; Ⅵ 滇西南地块。F1东昆仑断裂带; F2岷江-虎牙断裂带; F3龙门山断裂带; F4甘孜-玉树断裂带; F5鲜水河断裂带; F6安宁河断裂带; F7则木河断裂带; F8大凉山断裂带; F9马边-盐津断裂带; F10莲峰-昭通断裂带; F11小江断裂带; F12丽江-小金河断裂带; F13理塘断裂带; F14金沙江断裂带; F15德钦-中甸-大具断裂带; F16程海断裂带; F17红河断裂带; F18曲江断裂带; F19怒江断裂带; F20畹町断裂带; F21南汀河断裂带; F22龙陵-澜沧断裂带

Fig. 1 Spatial distribution of M≥7.0 earthquakes in the Tibet Plateau since 1900(a) and active block and fault zones in Sichuan and Yunnan area(b).

图 2 川滇地区ML≥3.0(a)、 ML≥4.0(b)地震的震源机制分布(地块和断裂同图 1)

Fig. 2 Spatial distribution of ML≥3.0(a), ML≥4.0(b)focal mechanism in Sichuan and Yunnan area(Blocks and faults are same as Fig. 1).

图 3 川滇地区各次级地块及断裂带地震的震源机制分类图

Fig. 3 Classification map of focal mechanisms of sub blocks and fault zones in Sichuan and Yunnan area.

表1 川滇地区各次级地块及断裂带地震震源机制类型的个数及比例

Table 1 Number and proportion of focal mechanism types of sub blocks and fault zones in Sichuan and Yunnan area

分区	地震总数	走滑型		逆冲型		正断型		不确定型
分区	地震总数	个数	比例/%	个数	比例/%	个数	比例/%	个数	比例/%
龙门山断裂带(F₃)	559	163	29	249	45	92	16	55	10
鲜水河断裂带(F₅)	98	58	59	16	17	12	12	12	12
安宁河-则木河断裂带(F₆-F₇)	65	37	57	12	18	9	14	7	11
马边-盐津断裂带(F₉)	51	20	39	16	31	7	14	8	16
莲峰-昭通断裂带(F₁₀)	75	42	56	14	19	11	15	8	10
小江断裂带(F₁₁)	59	31	53	15	25	7	12	6	10
丽江-小金河断裂带(F₁₂)	300	177	59	40	13	58	20	25	8
红河断裂带(F₁₇)	163	85	52	27	17	33	20	18	11
华南地块(四川盆地)(Ⅱ)	189	62	33	50	27	27	14	50	26
川西北地块(Ⅳ₁)	189	99	52	29	15	44	23	17	9
滇中地块(Ⅳ₂)	254	153	60	40	16	40	16	21	8
滇西地块(Ⅴ)	330	190	58	46	14	78	23	16	5
滇西南地块(Ⅵ)	198	100	51	29	14	48	24	21	11

图 4 川滇地区各次级块体及断裂带的应力主轴球面投影图

Fig. 4 Projection of principal stress axis of sub blocks and fault zones in Sichuan and Yunnan area.

表2 川滇地区各次级地块及断裂带的应力主轴参数

Table 2 Parameters of principal stress axis of sub blocks and fault zones in Sichuan and Yunnan area

分区	S₁		S₂		S₃		Var	R	应力类型	其他结果
分区	走向 /(°)	倾角 /(°)	走向 /(°)	倾角 /(°)	走向 /(°)	倾角 /(°)	Var	R	应力类型	S₁ /(°)	来源
龙门山断裂带(F₃)	87	1	3	18	180	72	0.28	0.45	逆冲	98	①
鲜水河断裂带(F₅)	113	3	56	87	157	1	0.26	0.72	走滑	80	②
安宁河-则木河断裂带(F₆-F₇)	118	18	133	45	13	40	0.32	0.66	走滑	127	①
马边-盐津断裂带(F₉)	122	4	30	31	141	58	0.31	0.33	逆冲	305	①
莲峰-昭通断裂带(F₁₀)	114	2	58	88	156	0	0.24	0.63	走滑	127	②
小江断裂带(F₁₁)	133	11	12	69	227	18	0.32	0.82	走滑	314	①
丽江-小金河断裂带(F₁₂)	166	3	7	87	104	1	0.26	0.41	走滑	147	②
红河断裂带(F₁₇)	166	21	48	65	71	13	0.30	0.51	走滑	169	②
华南地块(四川盆地)(Ⅱ)	104	8	12	16	41	72	0.32	0.48	逆冲	110~140	③
川西北地块(Ⅳ₁)	152	11	13	75	64	10	0.30	0.34	走滑	160~170	③
滇中地块(Ⅳ₂)	156	2	82	86	66	3	0.28	0.60	走滑	150~160	③
滇西地块(Ⅴ)	23	2	114	87	113	2	0.27	0.38	走滑	25	①
滇西南地块(Ⅵ)	24	16	131	73	116	7	0.31	0.41	走滑	16	①

图 5 模型长度与数据拟合误差之间的折中曲线图

Fig. 5 Trade-off curve between model length and data variance for the full range of possible values of damping parameter e.

图 6 川滇地区应力场的时空演化特征 a 1970年1月1日—2017年3月31日; b 1970年1月1日—2008年5月11日; c 2008年5月12日—2013年4月19日;d 2013年4月20日—2017年3月31日

Fig. 6 Spatial-temporal evolution of stress field in Sichuan and Yunnan area.

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