青藏高原东北缘老虎山断裂的断层面参数拟合及其几何意义

引用本文

刘白云, 尹志文, 袁道阳, 李亮, 王维欢. 青藏高原东北缘老虎山断裂的断层面参数拟合及其几何意义[J]. 地震地质, 2020,42(6): 1354-1369.
LIU Bai-yun, YIN Zhi-wen, YUAN Dao-yang, LI Liang, WANG Wei-huan. THE RESEARCH ON FAULT PLANE SOLUTION AND GEOMETRIC MEANING OF THE LAOHUSHAN FAULT IN THE NORTHEASTERN TIBETAN PLATEAU[J]. SEISMOLOGY AND GEOLOGY, 2020,42(6): 1354-1369. 复制到剪切板

DOI:10.3969/j.issn.0253-4967.2020.06.006
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青藏高原东北缘老虎山断裂的断层面参数拟合及其几何意义

刘白云^1,²⁾, 尹志文^1)),^*, 袁道阳³⁾, 李亮¹⁾, 王维欢¹⁾

1)甘肃省地震局, 兰州 730000

2)中国地震局地质研究所地震动力学国家重点实验室, 北京 100029

3)兰州大学, 兰州 730000

*通讯作者: 尹志文, 男, 1964年生, 高级工程师, 主要研究方向为地震监测预警, 电话: 0931-8276503, E-mail: 601242151@qq.com。

〔作者简介〕刘白云, 男, 1980年生, 2012年于中国地震局兰州地震研究所获构造地质学硕士学位, 高级工程师, 主要从事断层面参数、地震定位、地震成像等方面的研究, 电话: 0931-8271037, E-mail: 421121833@qq.com。

收稿日期: 2020-02-28

基金项目: 中国地震局地震预测研究所基本科研业务专项(2017IESLZ02)、中国地震局地质研究所地震动力学国家重点实验室开放基金(LED2020B01)、甘肃省自然科学基金(18JR3RA414)和甘肃省应急流动台网运维项目(ZX1903001)共同资助

摘要

文中利用2008—2019年甘肃和周边地震台网20个台站形成的观测报告, 以及中国地震科学台阵探测二期项目在南北地震带北段布设的18个流动观测台站于2014—2015年记录的老虎山地区小地震资料, 经双差定位方法重新进行了震源位置的修定, 获得了700个重新定位的震源资料。重新定位后, 研究区内小地震更加集中地沿老虎山断裂呈NW向线性分布, 震源深度也明显呈集中分布的趋势, 大部分地震均匀分布于0~10km深度范围, 显示出该区地震多为浅源地震的特征。依据成丛地震发生在断层附近的原则, 采用模拟退火算法及高斯-牛顿算法相结合的方式, 精确地获得了老虎山断裂断层面的详细参数(走向为103°、倾角为89°、滑动角为0°), 表明该断裂是一条NW走向的高倾角左旋断裂, 长约38km, 自SE从景泰喜集水(37.05°N, 104.05°E)延伸至NW的天祝松山(37.12°N, 103.66°E)。将所得结果与1990年天祝 M_S6.2地震和2000年景泰 M_S5.9地震的发震构造和震源机制解进行对比可知, 反演得到的断层面参数与前人的认识十分吻合。老虎山地表断裂与反演断层面在地表的投影线为相互平行关系, 且距离非常近。

关键词: 双差定位; 老虎山断裂; 断层面解; 发震构造

中图分类号:P315.2 文献标志码:A 文章编号:0253-4967(2020)06-1354-16

THE RESEARCH ON FAULT PLANE SOLUTION AND GEOMETRIC MEANING OF THE LAOHUSHAN FAULT IN THE NORTHEASTERN TIBETAN PLATEAU

LIU Bai-yun^1,²⁾, YIN Zhi-wen¹⁾, YUAN Dao-yang³⁾, LI Liang¹⁾, WANG Wei-huan¹⁾

1)Gansu Earthquake Agency, Lanzhou 730000, China

2)State Key Laboratory of Earthquake Dynamics, Institute of Geology, China Earthquake Administration, Beijing 100029, China

3)Lanzhou University, Lanzhou 730000, China

Abstract

The Laohushan fault zone is located in the northeast margin of the uplift area of the Tibetan plateau. It belongs to the eastern segment of the Laohushan-Maomaoshan-Jinqianghe Fault in the eastern segment of the North Qilian fault system. It was manifested as compressive thrust in early stage, but its mechanical properties changed into left-lateral strike-slip movement after middle Pleistocene. There occurred the Jingtai M_S6.8 earthquake in 1888, Tianzhu M_S6.2 earthquake in 1990 and Jingtai M_S5.9 earthquake in 2000 along the fault in history.
With the construction of the national important projects in earthquake industry-“Digital seismic network project of the 10th Five Year Plan” and “Chinese seismic background field detection project”, a number of modern seismological stations were built in Gansu Province and its adjacent areas. Contrast with seismographic network, the mobile broadband seismic array has the advantages of relatively dense stations, small spacing, uniform distribution, and high data integrity rate. Combining the two observational methods has gradually become the main development direction at home and abroad.
Based on the data of small earthquakes in the Laohushan zone recorded by 20 stations of the digital seismic network in Gansu and its adjacent seismic network during the years of 2008 to 2019, and 18 portable seismographic stations from the 2^nd-phase project of China Seismic Detection Array during the years of 2014—2015, we relocated the dense earthquakes by double-difference method and obtained the source parameters for 700 earthquakes. The accurately located small earthquakes distribute along both sides of the Laohushan Fault, which is NW-trending obviously. Most earthquakes distribute at the depth range of 0~10km of the earth's surface after the relocation, and the result shows that the focal depths are more concentrated.
Generally, the earthquakes are closely related to active tectonics, large earthquakes usually occur on fault zones with obvious activity, but the distribution of small earthquakes is related to the complex stress state underground and the complex structures of fault zones. We can inverse the shapes and positions of the fault planes using spatial distribution of hypocenters of small earthquakes according to the principle that clustered earthquakes occur near the faults. We obtained the parameters of the Laohushan Fault, which has a strike of 103°and a dip angle of 89°, by using the simulated annealing algorithm and the Gauss-Newton algorithm. On this condition, rake angle of the fault plane is further inferred from regional tectonic stress parameters. These inversion results of the fault parameters indicate that it's a left-lateral slip fault with a high dip angle and a length of 38km. It extends from Xijishui county town of Jingtai in the southeast to Songshan of Tianzh county town in the northwest. Comparing the inversion fault plane parameters and the focal mechanism solutions of the 1990 Tianzhu M_S6.2 and 2000 Jingtai M_S5.9 earthquakes, both of the results are identical. Besides, the spatial distribution of inverted fault plane and the location of Laohushan Fault by the previous studies are basically parallel.
In the past, the studies of active faults mainly focused on the qualitative researches of macroscopic survey. With the technological development of earthquake location and inversion method in recent years, many quantitative researches have gradually been carried out on the determination of active fault parameters. The inversion results of Laohushan fault plane and the previous studies on the geometric characteristics of the fault are verified each other. It is proved by facts that it's an important research means of active faults. It can provide more evidences for determining fault parameters by inversion.

Keyword: double-difference location approach; the Laohushan Fault; fault plane solution; seismogenic structures

文章图片

0 引言

老虎山断裂带位于青藏高原隆起区的东北缘, 属北祁连断裂系东段的老虎山-毛毛山-金强河断裂的东段, 其向E延伸并与海原断裂带左阶斜接, 向W与毛毛山活动断裂相连。该断裂全长78km, 整体走向为 N70°~80°W, 东起甘肃景泰县东南的老庄沟, 向W经老虎山、红灌沟、老虎沟、阿门岘、黑马圈河至独山为止(图 1)。其早期活动表现为挤压逆冲型, 中更新世以来, 其力学性质转变形成以左旋走滑为主(刘小凤等, 1994)。历史上沿该断裂发生过1888年景泰M_S6.8、 1990年天祝M_S6.2和2000年景泰M_S5.9地震。

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	图 1 老虎山断裂带地质构造图Fig. 1 Geological map of the Laohushan Fault.

前人通过对该断裂的地层划分(刘百篪等, 1994; 刘小凤等, 1994)和分段性(何文贵等, 1994)等地质学方面的研究给出了其可靠的活动断裂参数; 刘金瑞等(2018)基于LiDAR高精度地形数据, 综合多地点的左旋走滑位错量及不同时代的地貌面年龄数据, 利用蒙特卡洛模拟方法对其开展了研究, 所得结果表明该断裂表现为低滑动速率变化趋势; 孙赫等(2017)基于InSAR的海原-老虎山-毛毛山断裂带现今的地壳形变特征研究发现毛毛山—老虎山段两侧存在明显差异运动; 石富强等(2018)以GPS速度场为约束模拟研究了断层剪切力学性能对区域地壳运动速度场图像的控制作用, 进而在最优模型的基础上分析了当前青藏高原东北缘不同断裂的应力状态, 结果显示中段的金强河-毛毛山-老虎山断裂当前的应力率水平较高。这些研究更多地侧重于断裂危险性分析等方面, 无法据此了解断裂的三维结构。

近年来, 随着地震行业国家重大工程项目——中国“ 十五” 数字化台网项目和后期“ 中国地震背景场探测项目” 的建设, 甘肃及周边地区新建或改建了一批现代化地震观测台站, 形成了较为完备的数字地震监测体系。同时, 地震台阵观测(刘启元等, 2008; 邓文泽等, 2014; 太龄雪等, 2015; 张艺等, 2017)具有台站分布相对密集、台间距小且分布相对均匀的特点, 可进一步弥补固定监测的不足, 近年来也在中国大陆广泛开展观测。丰富的地震观测资料及一些效率更高的反演算法的提出, 使得采用小地震丛集性确定深部活断层几何形态的研究得以大规模开展。本文首先对收集整理到的研究区内中国二期地震科学台阵和甘肃及周边数字化地震台网记录的小地震资料进行双差地震精定位, 然后根据研究区小地震分布的密集程度, 沿老虎山断裂选择条带状区域, 再基于区内的地震采用模拟退火算法并结合高斯牛顿算法反演老虎山断裂的断层面参数, 所得结果有助于进一步了解老虎山断裂的三维结构。

1 研究方法

1.1 双差定位方法

地球内部断裂带的几何结构最初是由地震活动性来揭示的(Schaff et al., 2002), 地震活动性分析与传统活动构造研究的密切结合是推断地震构造最为直接的方法, 但这种研究依赖于地震定位精度。常规定位误差较大, 影响结果的可靠性。双差算法通过在各台站同时记录到的2个相邻事件的观测与理论计算走时差的残差(即双差)来确定其相对位置, 可消除共同模式的误差, 尤其是与速度结构横向变化以及台站接收有关的误差, 无须对台站进行校正和准确估计走时即可大幅度提高其相对定位精度(Waldhauser et al., 2002)。目前, 该方法已在地震构造研究中得到了广泛应用(杨智娴等, 2003; 朱艾斓等, 2005; 黄媛等, 2006)。

在三维网格节点的速度模型中, 对于同一个地震观测台站k、震源i和震源j之间的观测到时和理论到时之差的基本方程为

$\begin{array}{l} r_{k}^{i} - r_{k}^{j} = \overset{3}{\sum_{l = 1}} \frac{\partial T_{k}^{i}}{\partial x_{l}^{i}} Δ x_{l}^{i} + Δ τ^{i} + \int_{i}^{k} u d s - \overset{3}{\sum_{l = 1}} \frac{\partial T_{k}^{j}}{\partial x_{l}^{j}} Δ x_{l}^{j} - Δ τ^{j} - \int_{j}^{k} u d s \\ = \overset{3}{\sum_{l = 1}} \frac{\partial T_{k}^{i}}{\partial x_{l}^{i}} Δ x_{l}^{i} + Δ τ^{i} + \overset{M_{ik}}{\sum_{m = 1}} \overset{N}{\sum_{n = 1}} w_{mn} Δ u_{n} Δ s_{m} \\ - \overset{3}{\sum_{l = 1}} \frac{\partial T_{k}^{j}}{\partial x_{l}^{j}} Δ x_{l}^{j} - Δ τ^{j} - \overset{M_{jk}}{\sum_{m = 1}} \overset{N}{\sum_{n = 1}} w_{mn} Δ u_{n} Δ s_{m} \end{array}$ (1)

根据双差地震定位法, 如果震源i和震源j彼此相距足够近, 则可认为震源到同一个观测地震台站k的射线路径是相同的, 若速度结构已知, 则式(1)可简化为

$d r_{k}^{ij} = r_{k}^{i} - r_{k}^{j} = \overset{3}{\sum_{l = 1}} \frac{\partial T_{k}^{i}}{\partial x_{l}^{i}} Δ x_{l}^{i} + Δ τ^{i} - \overset{3}{\sum_{l = 1}} \frac{\partial T_{k}^{j}}{\partial x_{l}^{j}} Δ x_{l}^{j} - Δ τ^{j}$ (2)

$d r_{k}^{ij} = r_{k}^{i} - r_{k}^{j}$ 称为双差, 是2个相邻地震观测到时和理论到时之差:

$d r_{k}^{ij} = r_{k}^{i} - r_{k}^{j} = (T_{k}^{i} - T_{k}^{j})^{obs} - (T_{k}^{i} - T_{k}^{j})^{cal}$ (3)

观测到时差( $T_{k}^{i}$ - $T_{k}^{j}$ )^obs可通过相似波形的波形互相关技术及目录数据计算获得。将所有地震对(i, j=1, 2, …, N)、所有台站(k=1, 2, …)得到的形如式(3)的方程组成一个线性方程系统, 用矩阵形式表示为

$WGm = Wd$ (4)

在反演过程中, 对所有地震经重新定位的各震源参数(即3个方向上的坐标和发震时刻)加上使其平均移动(即矩心)为零的约束条件:

$\overset{N}{\sum_{i = 1}} Δ m_{i} = 0$ (5)

在实际计算中, 我们采用共轭梯度法求解上述方程, 得到阻尼最小二乘解, 同时将奇异值分解法应用于部分资料以获得有关模型参数的误差、分辨度等信息。

1.2 断层面拟合及滑动角确定的方法

大地震发生后的一定时间内或在断层蠕滑过程中, 大量小地震通常围绕在断层面及其附近发生。因此, 利用一定数量的小地震震源位置可反演得到断层面相关参数。其基本思路是寻求一个平面, 使所有小地震的震源位置到这个平面距离的平方和最小(王鸣等, 1992)。建立目标函数为所有小地震到断层面垂直距离与观测误差比值的平方和:

$E (ρ, φ, δ) = \overset{n}{\sum_{i = 1}} {(\frac{D_{i}}{σ_{i}})}^{2}$ (6)

寻找参数ρ 、 φ 、 δ 的值, 使得式(6)为最小值, 这时的φ 为所求断层的走向, δ 为所求断层的倾角。

虽然根据小地震的丛集程度可以判断断层的走向和倾角, 然而滑动角对于地震断层相互作用研究至关重要。基于一定的合理假定——地震断层错动方向与局部应力场在该断层面上作用的剪切应力方向一致, 万永革等(2008)给出了断层滑动角的估计方法: 设构造应力场P轴的走向为φ _P、俯角为δ _P, T轴的走向为φ _T、俯角为δ _T, 则在NE下地理坐标系中方向矢量可表示为

$T = (\cos φ_{T} \cos δ_{T}, \sin φ_{T} \cos δ_{T}, \sin δ_{T})$ (7)

$P = (\cos φ_{P} \cos δ_{P}, \sin φ_{P} \cos δ_{P}, \sin δ_{P})$ (8)

中间轴(B轴)的方向可由式(9)求得:

$B = P \times T$ (9)

在研究地震的震源机制和构造应力场之间的关系时, 经常引入表示主应力相对大小的量R(崔华伟等, 2019):

$R = \frac{S_{2} - S_{3}}{S_{1} - S_{3}}$ (10)

其中, S₁、 S₂ 和S₃为最大主应力、中间主应力和最小主应力。

根据前面得到的地震断层面走向φ 、倾角δ , 该断层的滑动方向和法向在NE下地理坐标系中可表示为

$l = (\cos φ, \sin φ, 0)$ (11)

$m = (- \sin φ \cos δ, \cos φ \cos δ, \sin δ)$ (12)

$n = (\sin φ \sin δ, - \cos φ \sin δ, \cos δ)$ (13)

其中, l、 m、 n分别为断层面的走向、沿断层面向下方向和法向。将主轴坐标系中的应力张量(式)表示在断层坐标系l、 m和n中, 则沿断层走向和倾向的应力可表示为

$T_{1} = \cos (T, n) \cos (T, l) S_{1} + \cos (B, n) \cos (B, l) S_{2} + \cos (P, n) \cos (P, l) S_{3}$ (14)

$T_{2} = \cos (T, n) \cos (T, m) S_{1} + \cos (B, n) \cos (B, m) S_{2} + \cos (P, n) \cos (P, m) S_{3}$ (15)

这样, 滑动角可表示为:

$γ = ta n^{- 1} \frac{T_{2}}{T_{1}}$ (16)

解决上述反演问题的传统做法有局部算法和全局算法, 这2种方法依赖初始解, 如果初始解选取得不合适, 得到的解将会远离真实解。万永革等(2008)发展了模拟退火全局搜索和高斯牛顿局部搜索相结合的方法解决上述问题, 避免了依赖初始解的缺陷, 不仅能在全局搜索最优解, 而且可以估计参数的误差, 并且在求得大地震断层面后还可以根据区域构造应力场参数估计断层面上滑动角, 因此被广泛应用于断层参数确定研究中(刘白云等, 2012, 2014, 2015; 李峰等, 2017; 韩晓明等, 2018; 林群等, 2018)。

2 研究数据处理与分析

2.1 研究区地震的双差定位结果及分析

本文在定位过程中收集了来自甘肃及周边测震台网共20个台站(包括甘肃地震台网11个固定测震台、青海地震台网6个固定测震台、内蒙古地震台网1个固定测震台和宁夏地震台网2个固定测震台)2008年1月—2019年12月的地震观测报告资料, 以及基于中国地震科学台阵探测二期项目布设在南北地震带北段的18个台站2014—2015年记录的资料经定位形成的观测报告, 各类台站的分布情况见图 2。在收集到资料中, 震中位于本文研究区(36.9°~37.3°N, 102.9°~104.1°E)内的地震共有833次, 震级分布范围为M_L0.1~5.0, 包含Pg震相5 581个, Sg震相5 042个。

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	图 2 青藏高原东北缘地区的主要断裂及地震台站分布(白色方框为本文研究区域)Fig. 2 Spatial distribution of main faults and stations in the northeastern Tibetan plateau (white thick rectangle denotes research area in this paper).

地震定位结果不仅涉及定位方法的选择, 而且与研究区定位所采用的初始结构模型紧密联系。本文进行地震双差定位反演所采用的初始模型(图 3)参考了该地区人工地震、层析成像等研究结果(李松林等, 2002; 周民都, 2006), 空间任意点的速度值均利用线性插值求得。

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	图 3 双差定位时采用的初始一维P波速度模型Fig. 3 1-D initial velocity model used for double difference relocation.

基于上述收集并整理好的地震观测资料用共轭梯度法(LSQR)求解方程。在读取震相到时时, 不同震相读数的精度各不相同, 往往需要对不同质量的数据作加权处理。一般情况下, 由于P波到时的读取质量优于S波, 故对2种震相分别赋予1.0和0.5的权重。针对研究区内小地震较多、台站分布较密集的特点, 选取台站与地震的间距为200km、地震对的间距为10km。最终共有700个地震得到了重新定位结果, 定位均方根残差从重新定位前的0.63s降为0.15s。从重新定位前(图 4)、后(图 5)的地震空间分布图像来看, 重新定位后的地震相对更加集中分布于老虎山断裂带两侧。

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	图 4 研究区重新定位前的小地震震中分布图(五角星代表M6.2和M5.8强震震中) F₁老虎山断裂Fig. 4 Map view of microseismicity before relocation in the research area(red stars denote two strong earthquakes).

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	图 5 研究区重新定位后的小地震震中分布图(粗黄色方框为本文反演区域)Fig. 5 Map view of microseismicity after relocation in the research area (thick yellow rectangles denote inversion region in this paper).

震源深度是探讨地震孕育和发生的深部环境、地壳变形特性及其力学性质、属性以及圈层构造等诸多大陆动力学问题的重要参数(张国民等, 2002)。分析重新定位前、后地震的震源深度分布频度可知(图 6), 重新定位前研究区内地震的震源深度集中分布于5~10km, 重新定位后0~5km深度范围内的地震频度明显加大, 成为新的震源优势集中层。即重新定位后, 这一区域地震的震源深度呈明显集中的趋势, 大部分地震都均匀分布在0~10km之间, 显示出该区地震震源深度较浅的特征。而这一特征与该区历史上发生的1990年天祝M_S6.2和2000年景泰M_S5.9地震的主震及其余震的震源深度分布特征总体一致(才树华等, 1992)。同时, 后文反演的断层面整体埋深也在上述深度范围内。这或许是由于青藏块体的快速抬升和在本区NE向推挤的过程中遇到阿拉善块体和鄂尔多斯块体的阻挡, 在这一地区形成了弧形断裂组成的断裂束, 而这些断裂束的新活动性强、埋深浅, 故在活动过程中形成了一系列震源深度较浅的地震所致。

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	图 6 研究区小地震重新定位前(a)、后(b)的震源深度统计图Fig. 6 Statistics of focal depths of small earthquakes before(a)and after(b)relocation in the research area.

2.2 断层面参数反演及分析

根据老虎山断裂附近小地震的重新定位结果、断裂两侧小地震的展布特点以及断裂的位置和走向, 沿断裂选定了矩形区域内小地震事件(图 5)进行断层面参数反演, 结合模拟退火算法和高斯牛顿算法, 求得老虎山断裂的走向、倾角、距坐标原点的距离及断层的4个顶点的位置(表1)。

表1 使用重新定位的小地震资料反演得到的老虎山断裂的断层面走向、倾角和位置 Table1 Fault plane parameters determined using relocation results of small earthquakes

反演得到的断层近直立(图7c)。由于选择用于反演断层面的地震基本沿断层呈均匀对称分布, 故得到的小地震与反演断层面距离的分布频度(图7d)也基本呈对称分布, 表明大部分小地震分布在所求断层面的附近。

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图 7 老虎山断裂重新定位的小地震分布在水平面(a)、断层面(b)和垂直于断层面的横断面(c)上的投影; d 小地震与断层面距离的分布情况
圆圈表示精确定位的小地震, 粗实线表示确定的断层面边界; AA'为断层上边界的端点; SD为走向, DD为倾向, DF为与断层面的距离Fig. 7 Distribution of relocated small earthquakes near the Laohushan Fault. (a)The map view. (b)Vertical cross-section along the fault plane. (c)Vertical cross-section perpendicular to the fault plane. (d)Histogram of small earthquakes sorted by their distances to the fault plane.

通过反演计算拟合出断层的走向约为103°, 即N77°W; 倾角为89°, 即为近直立的高倾角断层; 其下界埋深约14km, 上界埋深约2km(图7c), 表明该断裂的基础深度位于上地壳内; 长约38km, 由SE从景泰喜集水(37.05°N, 104.05°E)延伸至NW向的天祝松山(37.12°N, 103.66°E)。反演得到的断层面的顶点位置见表1。

从反演结果来看, 断层的走向、倾角和空间展布(图7a)与地震地质和其他研究方式得到的该断裂的几何特征非常吻合。

2.3 断层滑动角参数的确定及分析

在研究地震震源机制和构造应力场之间的关系时, 不仅需要知道应力场P轴的走向φ _P和俯角δ _P、 T轴的走向φ _T和俯角δ _T, 还需引入表示主应力相对大小的量R。卜玉菲等(2013)将甘肃及其邻区划分为1°×1°的子区, 利用甘肃及邻区2001年以来245个M_L≥ 3.5地震的震源机制解数据, 由多个震源机制解反演该区平均应力场, 给出了覆盖甘肃及邻区的1°×1°的构造应力场方向和相对大小, 该结果中就包括本研究涉及的老虎山地区的构造应力场和R值结果。

考虑到断裂活动受大尺度构造应力场的控制, 选取其研究结果中能代表该区域的构造应力场参数(表2)。

表2 研究区的局部应力场参数 Table2 Regional stress field of Laohushan zone

假定P轴和T轴的走向误差为5°, 倾伏角误差为10°, 根据前文得到的断层面走向、倾角及其标准差, 采用表2中的局部应力场参数及其标准差求解滑动角及其标准差, 得到老虎山断裂的滑动角为0°, 标准差为9°, 表明其滑动性质为纯左旋走滑。该结果也与地质学考察的结果非常一致。

3 研究区内2次强震的发震构造与反演结果关系的讨论

1990年以来, 发生于老虎山断裂的2次强震分别为1990年天祝M_S6.2和2000年景泰M_S5.9地震(荣代潞等, 2001; 陈军营等, 2009)。前人对这2次地震的地震烈度、发震构造、震源机制解等方面进行了研究, 结果表明这2次强震的震中区长轴均呈NW向展布。 1990年天祝M_S6.2地震的余震以主震为中心呈NW向丛状分布, 余震大体沿左旋方向迁移发生, 据此推测发震构造为左旋运动(才树华等, 1992)。另外, 这2次地震震源机制解的节面I走向为96°~98°(表3), 与老虎山断裂的产状吻合。再结合地震灾害损失调查和烈度衰减特征分析, 即可认为这2次强震的孕震和发震构造均为老虎山断裂。

表3 1990年天祝M_S6.2和2000年景泰M_S5.9地震的震源机制解(据美国哈佛大学) Table3 Focal mechanism solutions of the Tianzhu M_S6.2 earthquake in 1990 and the Jingtai M_S5.9 earthquake in 2000(based on results of Harvard University)

本文反演得到的断层面参数与2次强震的震源机制解和基于余震推测的断裂滑动性质均非常一致。从反演的断层位置与2000年景泰M_S5.9地震烈度圈的关系来看, 其与2000年景泰M_S5.9地震烈度圈的长轴走向也是一致的(图 8), 上述多个方面的比较结果说明此次反演结果是真实可信的。

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	图 8 2000年景泰M_S5.9地震等震线图(据王书明等, 2001)与反演断层之间的关系Fig. 8 The relationship of inversion fault and isoseismal map of the Jingtai M_S5.9 earthquake in 2000.

此外, 为了更清楚地显示研究区地表断裂、反演断层面、精定位小地震之间的分布情况及相互关系, 我们绘制了它们的三维立体分布图(图 9)。从图 9 可以清晰地看出, 老虎山地表断裂与反演断层面在地表的投影线相互平行, 且距离非常近。反演的断层面近直立, 与纯走滑断层的产状特征一致。反演断层面内精定位小地震密集分布。

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	图 9 研究区地表断裂、反演断层面、精定位小地震震源三维立体分布图Fig. 9 3-D stereoscopic distribution map of the surface fracture, inversion fault plane and relocations of small earthquakes in the research area.

4 结论

本文首先利用双差定位法, 基于研究区内2008—2019年的台网和台阵观测数据对小地震进行了重新定位。之后, 根据精定位后的小地震分布和断层位置, 沿着老虎山断裂选定重新定位的小地震事件进行断层面参数反演, 结合模拟退火全局搜索和高斯牛顿局部搜索方法, 获得了老虎山断裂断层面的走向、倾角、位置及相应的误差, 并基于区域应力场参数反演了该断层面上的滑动角。最后, 将所得计算结果与前人分析的研究区内2次强震发震构造的几何特性以及地质学认为的老虎山断裂的空间展布情况进行了比较, 获得了以下主要结论:

(1)反演到的断层面走向为N77°W, 标准差为0.2°; 产状近直立; 滑动角为0°, 标准差为0.7°; 综合说明该断裂是一条NW走向的高倾角纯左旋走滑断裂。

(2)从前述内容来看, 无论是老虎山断裂本身的几何产状还是2次强震发震构造的研究成果, 前人对该断裂空间几何展布认识是统一的。本文绘制的老虎山断裂的分布图引用了何文贵等(1994)给出的结果。由于本文的研究区域较小, 图示的误差可以忽略不计。另外, 从结论(1)可以看出, 反演得到断层面的走向和滑动角的误差均< 1°, 故可认为本研究反演得到的断层面位置及地质学描述的老虎山地表断裂的位置均是可信的。比较两者的空间位置可知, 老虎山地表断裂与反演得到的断层面在地表的投影线相互平行, 且距离非常近。反演得到的断层面即为地表断裂在深部的延伸。

(3)对比反演结果及已有的1990年天祝M_S6.2和2000年景泰M_S5.9地震发震构造的几何性质结果并开展分析可知, 反演得到的老虎山断裂的断层参数与地质考察、震源机制研究等方面的认识十分吻合。此外, 反演得到断层与2000年景泰M_S5.9地震烈度圈的长轴走向一致。

以往对活动断裂的研究多以野外宏观调查的定性研究为主。近年来, 随着地震定位和反演技术的发展, 一些针对活动断裂参数确定的定量化研究也逐渐实施和开展。本文对老虎山断裂的断层面参数和滑动角的反演结果, 可在地震学研究方面与前人对该断裂的几何学特征研究相互印证。事实证明, 断层面参数反演法为研究活动断裂几何学特征的一种重要手段, 可为确定活动断裂相关参数提供更加充分的证据。

致谢本研究使用了万永革研究员提供的断层面计算程序, 在此表示衷心感谢!

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[20]	石富强, 邵志刚, 占伟, 等. 2018. 青藏高原东北缘活动断裂剪切模量及应力状态数值模拟[J]. 地球物理学报, 61(9): 3651—3663. doi: DOI: 106038/cjg2018L0631. SHI Fu-qiang, SHAO Zhi-gang, ZHAN Wei, et al. 2018. Numerical modeling of the shear modulus and stress state of active faults in the northeastern margin of the Tibetan plateau[J]. Chinese Journal of Geophysics, 61(9): 3651—3663(in Chinese). [本文引用:1]
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[22]	太龄雪, 高原, 刘庚, 等. 2015. 利用中国地震科学台阵研究青藏高原东南缘地壳各向异性: 第一期观测资料的剪切波分裂特征[J]. 地球物理学报, 58(11): 4079—4091. doi: DOI: 106038/cjg20151116. TAI Ling-xue, GAO Yuan, LIU Geng, et al. 2015. Crustal seismic anisotropy in the southeastern margin of Tibetan plateau by ChinaArray data: Shear-wave splitting from temporary observations of the first phase[J]. Chinese Journal of Geophysics, 58(11): 4079—4091(in Chinese). [本文引用:1]
[23]	万永革, 沈正康, 刁桂苓, 等. 2008. 利用小震分布和区域应力场确定大震断层面参数方法及其在唐山地震序列中的应用[J]. 地球物理学报, 51(3): 793—804. WAN Yong-ge, SHEN Zheng-kang, DIAO Gui-ling, et al. 2008. An algorithm of fault parameter determination using distribution of small earthquakes and parameters of regional stress field and its application to Tangshan earthquake sequence[J]. Chinese Journal of Geophysics, 51(3): 793—804(in Chinese). [本文引用:2]
[24]	王书明, 林长佑, 陈军营. 2001. 景泰5. 9级地震后大地电磁跟踪监测研究[J]. 西北地震学报, 23(3): 297—300. WANG Shu-ming, LIN Chang-you, CHEN Jun-ying. 2001. Magnetotelluric monitoring after the Jingtai M_S5. 9 earthquake[J]. Northwestern Seismological Journal, 23(3): 297—300(in Chinese). [本文引用:1]
[25]	王鸣, 王培德. 1992. 1989年10月18日大同-阳高地震的震源机制和发震构造[J]. 地震学报, 14(4): 407—415. WANG Ming, WANG Pei-de. 1992. The mechanism and seismogenic structure of Datong-Yanggao earthquake which occurred on Oct 18, 1989[J]. Acta Seismologica Sinica, 14(4): 407—415(in Chinese). [本文引用:1]
[26]	杨智娴, 陈运泰, 郑月军, 等. 2003. 双差地震定位法在我国中西部地区地震精确定位中的应用[J]. 中国科学(D辑), 33(S1): 129—134. YANG Zhi-xian, CHEN Yun-tai, ZHENG Yue-jun, et al. 2003. Relocation of earthquakes in central-western China using the double difference earthquake location algorithm[J]. Science in China(Ser D), 33(S1): 129—134(in Chinese). [本文引用:1]
[27]	张艺, 高原. 2017. 中国地震科学台阵两期观测资料近场记录揭示的南北地震带地壳剪切波分裂特征[J]. 地球物理学报, 60(6): 2181—2199. doi: DOI: 106038/cjg20170613. ZHANG Yi, GAO Yuan. 2017. The characteristics of crustal shear-wave splitting in North-South seismic zone revealed by near field recordings of two observation periods of ChinaArray[J]. Chinese Journal of Geophysics, 60(6): 2181—2199(in Chinese). [本文引用:1]
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[30]	朱艾斓, 徐锡伟, 胡平, 等. 2005. 首都圈地区小震重新定位及其在地震构造研究中的应用[J]. 地质论评, 51(3): 268—274. ZHU Ai-lan, XU Xi-wei, HU Ping, et al. 2005. Relocation of small earthquakes in Beijing area and its implication to seismotectonics[J]. Geological Review, 51(3): 268—274(in Chinese). [本文引用:1]
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[32]	Waldhauser F, Ellsworth W L. 2002. Fault structure and mechanics of the Hayward Fault, California, from double-difference earthquake locations[J]. Journal of Geophysical Research: Solid Earth, 107(B3): 1—15. [本文引用:1]

2013

0.0

卜玉菲, 万永革, 张元生. 2013. 甘肃及邻近地区的构造应力场[J]. 地震地质, 35(4): 833—841. doi: DOI: 103969/j. issn. 0253-4967. 2013. 04. 012.

Yu-fei

, WAN

Yong-ge

, ZHANG

Yuan-sheng

. 2013. Tectonic stress analysis in Gansu and its adjacent areas[J]. Seismology and Geology, 35(4): 833—841(in Chinese).

Gansu and its adjacent areas are on the northeastern margin of the Qinghai-Tibet plateau. The study area locates at the junction of Alashan,Qilian,Qaidam and Ordos blocks. The tectonic structure is complicated in this area. The research of tectonic stress field in the study area has an important scientific significance for earthquake prediction of Gansu. Characteristics of present-day tectonic stress field is studied based on 245 M L ≥3.5 focal mechanism solutions since January 2001 to June 2012 in Gansu and its adjacent areas. For solving the stress field,we follow Wan's(2000)method to solve the rake angle according to two nodal planes' strikes and dips of the focal mechanisms. We treat the stress tensor solution of each fault plane as the optimal solution of the area when the slip on the fault plane minus the angle between shear stress direction and strike is minimal. We use F test to get the confidence interval of the four parameters, as well as the confidence interval of the principal compressive and tensile stress axes. We divide the whole area into 1°×1°grids. In order to cover the whole study region and get the smoothed stress field,we select the data within the square areas of 2°×2° centered at the grid point. The direction and the relative size of the tectonic stress field in 2°×2° grid in Gansu and its adjacent areas are presented for the first time. These results show that the dip angles of maximum principal compressive stress axes of the whole region are generally small. And the dip angles of maximum principal tensile stress axes vary widely,which are small in the western part,and relatively larger in the east. It indicates that the tectonic stress field with horizontal action of compression acts as the major in the west. Many deep large strike-slip faults in Qilian seismic belt correspond with the results. The geological structure of southeastern area of Gansu is complex,and the characteristics of stress field indicate that strike-slip reverse faulting is likely to occur. Result of the inverted tectonic stresses also shows that maximum principal compressive stress axis strikes near NE on the plate margin of Tibet plateau. This is caused by Qinghai-Tibet plateau moving to the northeast. At the outer edge of the Tibet plateau plate,its strikes show a radiated pattern,i.e. NS in west part,NNE in the middle section,and NNW in the east. The reason is that Qinghai-Tibet plateau,when moving to the northeast,is encountered with stable Ordos and Alashan blocks,therefore the material moves to southeast. The stress directions show that the source of the stress field in Gansu and its adjacent areas is extrusion of the India plate to Eurasian plate. Our inversion results are similar with the previous results,indicating the correctness of the approach. The relative stress values are more than 0.5 in the western areas and less than 0.5 in the eastern areas. According to Wan's research(2011), the maximum principle compressive stress solutions are more reliable in the western area,while the maximum principle tensile stress solutions are more reliable in the eastern areas. The results indicate a non-uniform stress field spatial distribution in Gansu area,and have certain reference significance for explaining the seismo-geological background and earthquake prediction research.

1 Lanzhou Institute of Seismology, China Earthquake Administration, Lanzhou 730000, China; 2 Institute of Disaster Prevention Science and Technology, Sanhe 065201, China

构造应力场对地震预测具有十分重要的科学意义。文中搜集了甘肃及邻区2001年以来245个 M L ≥3.5的震源机制解数据，由多个震源机制解反演该区平均应力场，首次给出了覆盖甘肃及邻区的1°×1°的构造应力场方向和相对大小。反演结果显示，青藏高原板块内缘最大主压应力呈NE向分布，外缘最大主压应力由西向东呈现出顺时针旋转的特征，即最大主压应力轴由西段近NS向转向中段NNE向，到东段转至NNW向。该区力源来自印度板块向欧亚板块的挤压。反演结果与前人的研究结果具有相似性，印证了处理方法的正确性，并且反演得到了甘肃地区的非均匀应力场的空间分布，这些结果为解释甘肃地区的地震地质背景和地震预测研究具有一定参考意义。

... 卜玉菲等(2013)将甘肃及其邻区划分为1°×1°的子区, 利用甘肃及邻区2001年以来245个M_L#cod#x02265 ...

1992

0.0

... 9地震的主震及其余震的震源深度分布特征总体一致(才树华等, 1992) ...

... 2地震的余震以主震为中心呈NW向丛状分布, 余震大体沿左旋方向迁移发生, 据此推测发震构造为左旋运动(才树华等, 1992) ...

2009

0.0

... 陈军营等, 2009) ...

2019

0.0

崔华伟, 万永革, 黄骥超, 等. 2019. 帕米尔—兴都库什地区构造应力场反演及拆离板片应力形因子特征研究[J]. 地球物理学报, 62(5): 1633—1649. doi: DOI: 106038/cjg2019M0202.

CUI

Hua-wei

, WAN

Yong-ge

, HUANG

Ji-chao

, et al. 2019. Inversion for the tectonic stress field and the characteristic of the stress shape factor of the detachment slab in the Pamir-Hindu Kush area[J]. Chinese Journal of Geophysics, 62(5): 1633—1649(in Chinese).

... 在研究地震的震源机制和构造应力场之间的关系时, 经常引入表示主应力相对大小的量R(崔华伟等, 2019): ...

2014

0.0

邓文泽, 陈九辉, 郭飚, 等. 2014. 龙门山断裂带精细速度结构的双差层析成像研究[J]. 地球物理学报, 57(4): 1101—1110. doi: DOI: 106038/cjg2014408.

DENG

Wen-ze

, CHEN

Jiu-hui

, GUO

Biao

, et al. 2014. Fine velocity structure of the Longmenshan fault zone by double-difference tomography[J]. Chinese Journal of Geophysics, 57(4): 1101—1110(in Chinese).

Using P-wave travel time data recorded by the Western Sichuan movable seismic array and the earthquake emergency response stations during May 2008 to October 2008, we obained accurate relocation of Wenchuan earthquake sequence and 3D P-wave seismic velocity structure by double-difference tomography. The results show that aftershock relocation by joint-inversion is similar to that based on 1-D velocity model by double-difference relocation; the P-wave velocity of Longmenshan fault zone region in 0 similar to 15 km is closely correlated with local geology, and the region in 20 similar to 30 km shows NE-NW cross structure. The south segment of Longmenshan fault zone is imaged as high P-wave velocity region in upper crust, the structure heterogeneity controls the distribution of aftershocks and the direction of propagation. The joint-inversion result also proves the existence of Xiaoyudong-Lixian buried fault, we also found that the NE segment of rupture zone may extend in new fault. The results confirm the Wenchuan earthquake as a high-angle listric thrust, and also confirm that the Yingxiu-Beichuan fault and Guanxian-Jiangyou fault merge into a shear belt at the depth of 20 km.

[Deng Wen-Ze; Chen Jiu-Hui; Guo Biao; Liu Qi-Yuan; Li Shun-Cheng; Li Yu; Yin Xin-Zhong; Qi Shao-Hua] China Earthquake Adm, State Key Lab Earthquake Dynam, Inst Geol, Beijing 100029, Peoples R China.

利用川西流动地震台阵、汶川地震震后应急台网记录到的P波到时资料，对2008年5月至2008年10月期间发生的汶川地震余震序列应用双差层析成像方法进行了地震震源和三维P波速度结构的联合反演.结果显示，联合反演获得的地震重定位结果与基于一维地壳参考模型的双差定位方法结果相近；研究区15 km以上速度结构与地表断裂分布密切相关，20 km以下深度呈现北东向和北西向交错结构.汶川地震破裂带南段龙门山断裂带之间上地壳呈现高速异常，速度结构的非均匀变化是控制余震分布和主震破裂传播的主要因素；联合反演结果给出了小鱼洞—理县方向存在隐伏断裂的速度结构证据，同时发现，破裂带北东段可能沿新发断裂扩展；结果确认了汶川地震起始段的高角度逆冲断裂特征，也确认了前山断裂和中央断裂在约20 km深度合并到脆韧转换带的特征.

... 邓文泽等, 2014 ...

2018

0.0

... 韩晓明等, 2018 ...

1994

0.0

... 刘小凤等, 1994)和分段性(何文贵等, 1994)等地质学方面的研究给出了其可靠的活动断裂参数 ...

... 本文绘制的老虎山断裂的分布图引用了何文贵等(1994)给出的结果 ...

2006

0.0

黄媛, 杨建思, 张天中. 2006. 2003年新疆巴楚-伽师地震序列的双差法重新定位研究[J]. 地球物理学报, 49(1): 162—169.

HUANG

Yuan

, YANG

Jian-si

, ZHANG

Tian-zhong

. 2006. Relocation of the Bachu-Jiashi, Xinjiang earthquake sequence in 2003 using the double-difference location algorithm[J]. Chinese Journal of Geophysics, 49(1): 162—169(in Chinese).

Combining the data recorded at the mobile seismic network with those from the regional network, we relocated the 404 aftershock sequence including 404 events of ML≥35 for the 2003 BachuJiashi, Xinjiang MS68 earthquake by the doubledifference method and made theoretical analysis of the feasibility. We gota result of significant improvement. Compared with the original result, the relocation makes the image of earthquake distribution become more convergent and more consistent with the intensity investigation and the source mechanism. The dominant distribution of focal depths is in the range 15～25km and the result is more consistent with the local geologic setting that there is a low velocity sediment layer above the depth 10 km.The arrival time residuals reduce to 024s from 394s. The horizontal average error is estimated to be less than 11km and the vertical average error can been controlled less than 24km.

Institute of Geophysics, China Earthquake Administration, Beijing 100081, China

将近台记录和区域台网数据联合用于双差地震定位算法，对2003年新疆巴楚-伽师MS68强震后404个ML≥35余震序列进行双差法重新精确定位，并对其进行了理论上的可行性分析. 精定位后定位结果与传统定位方法的原始定位结果进行比较发现：（1）精定位后震中分布图像更加集中，与当地的烈度考察和震源机制解结果更加协调；（2）震源深度优势分布集中在15～25km以内，与当地存在深度为10km以上低速沉积层的地质构造情况相一致；（3）精定位后定位残差由原来的394s降为024s，水平向估算误差平均可控制在11km以内，垂直向估算误差平均可控制在24km.

... 黄媛等, 2006) ...

2017

0.0

... 李峰等, 2017 ...

2002

0.0

李松林, 张先康, 张成科, 等. 2002. 玛沁—兰州—靖边地震测深剖面地壳速度结构的初步研究[J]. 地球物理学报, 45(2): 210—217.

Song-lin

, ZHANG

Xian-kang

, ZHANG

Cheng-ke

, et al. 2002. A preliminary study on the crustal velocity structure of Maqin-Lanzhou-Jingbian by means of deep seismic sounding profile[J]. Chinese Journal of Geophysics, 45(2): 210—217(in Chinese).

A 1000km long comprehensive geophysical profile was deployed along Marqin—Lanzhou—Jingbian for studying interaction between the Qinghai Xizang plateau block and the Ordos block and for studying the deep driving mechanism of tectonic deformation. A preliminary result is presented in this paper on the basis of deep seismic sounding （DS） data. The crust is clearly stratified. On the whole, it can be divided into two parts, i.e. the upper crust and the lower crust. Each on the two parts contains a number of secondary interfaces. The crust becomes gradually thicker from northeast to southwest mainly due to the variation in the depth of the lowr crust. The average crustal velocity becomes gradually lower from northeast to southwest—velocity is obviously low in the west of Zeku and in Haiyuan region. A number of low velocity layers exist in the west of Zeku, and another low velocity layer exists near Haiyuan. The number of reflecting horizons increases gradually from northeast to southwest. As seismic reflection waveform shows, Pc wave is very strong and lasts long at Haiyuan. Besides, the complexity coefficients of Pm wave in Haiyuan and in the west of Zeku are, much larger than those in other parts. The above results clearly show that anomalous structures exists in the crust and upper mantle in the west of Zeku and in Haiyuan region, which reflects the interaction between BayanHar block and Chaidamu block as well as between Qilian block and Ordos block. [

Research Center of Exploration Geophysics, CSB, Zhengzhou 450002, China

为研究青藏高原块体和鄂尔多斯地块间的相互作用和构造变形的深部驱动机制,布设了1000km长的玛沁-兰州-靖边综合地球物理探测剖面.本文只介绍由人工地震观测资料所得到的初步结果.地壳分层性明显,以C界面为界,总体上可分为上、下地壳两大部分,每个部分又包含一些次一级的界面;横向变化的总趋势是从东北至西南地壳逐渐变厚,地壳厚度的变化主要由下地壳厚度的变化所引起;地壳平均速度,总的变化趋势是自东北向西南逐渐降低,其中在泽库以西和海原地区的速度值明显偏低;在泽库以西存在多个壳内低速层,在海原附近存在一个低速层;壳内反射界面,沿测线由东北至西南逐步增多;从地震反射波形来看,在海原地区Pc波非常强,且延续时间长;另外,在海原地区和泽库以西地区Pm波的复杂性系数很大,远远大于其他地段的值.以上结果表明,泽库以西地区和海原地区地壳-上地幔存在着明显结构异常,反映了巴颜喀拉地块和柴达木地块、祁连地块和鄂尔多斯地块间的相互作用

... 本文进行地震双差定位反演所采用的初始模型(图 3)参考了该地区人工地震、层析成像等研究结果(李松林等, 2002 ...

2018

0.0

... 林群等, 2018) ...

1994

0.0

... 前人通过对该断裂的地层划分(刘百篪等, 1994 ...

2012

0.0

... 万永革等(2008)发展了模拟退火全局搜索和高斯牛顿局部搜索相结合的方法解决上述问题, 避免了依赖初始解的缺陷, 不仅能在全局搜索最优解, 而且可以估计参数的误差, 并且在求得大地震断层面后还可以根据区域构造应力场参数估计断层面上滑动角, 因此被广泛应用于断层参数确定研究中(刘白云等, 2012, 2014, 2015 ...

2014

0.0

刘白云, 曾文浩, 袁道阳, 等. 2014. 1954年腾格里沙漠北7级地震断层面参数和滑动性质研究[J]. 地震工程学报, 36(3): 622—627. doi: DOI: 103969/j. issn. 1000-0844. 2014. 03. 0622.

LIU

Bai-yun

, ZENG

Wen-hao

, YUAN

Dao-yang

, et al. 2014. Fault parameter and sliding behavior determination of the 1954 northern Tenggeli desert M7. 0 earthquake[J]. China Earthquake Engineering Journal, 36(3): 622—627(in Chinese).

The northern Tengger Desert M7.0 great earthquake that occurred in 1954 resulted in varying degrees of damage in many areas of Neimenggu and its adjacent regions.Thus far，research results of the cause of this earthquake are few and inconsistent.Because it occurred in the Gobi Desert，the aeolian effect of was intense.These facts cause difficulties in studying the earthquake through geological prospecting methods.It is known that clustered small earthquakes often occur in the fault plane vicinities of large earthquakes.We used precisely relocated earthquakes that occurred near the earthquake rupture zone between 1985 and 2012 and selected a strip-shaped zone according to clustered small earthquakes and long-axis morphology in the meizoseismal area.On the basis of simulated annealing and Gauss-Newtonian nonlinear inversion algorithms，we obtained fault plane parameters of earthquakes such as strike，dip，and location by using data of densely populated small events.On this condition，rake angles of the fault plane are further inferred from regional tectonic stress parameters.Finally，we determine that the inverted results and known results are similar and that the former are in the cycle of the highest seismic intensity.These findings indicate that the inverted results are reliable.

1954年腾格里沙漠北发生7级大震，由于此次地震发生在戈壁深处，风沙作用强烈，震后破坏现象不易保存，给通过地质踏勘研究地震增加了难度。到目前为止，涉及此次地震的发震构造研究内容较少。本研究根据成丛小震发生在大震断层面附近的原则及参考前人给出极震区长轴形态，采用1985—2012年发生在地震破裂区的精定位地震目录，选定了一个长条状研究区域，将模拟退火算法和高斯一牛顿算法结合，给出了利用小震密集程度求解的主震断层面走向、倾角，并确定地震发震断裂的长度、位置。在此基础上考虑区域构造应力参数，给出已求得断层面上的滑动角。最后将反演结果与已有结果做了对照，显示反演结果与已有的结果基本一致，反演到的震源断层位于前人给出的此次地震等震线的最高烈度圈内表明反演结果是真实可信的。

2015

0.0

刘白云, 曾文浩, 袁道阳, 等. 2015. 1927年古浪8级大地震断层面参数和滑动性质[J]. 地震地质, 37(3): 818—828. doi: DOI: 10969/j. issn. 0253-4967. 2015. 03. 012.

LIU

Bai-yun

, ZENG

Wen-hao

, YUAN

Dao-yang

, et al. 2015. The research on fault parameter and sliding behavior of the 1927 Gulang M8. 0 earthquake[J]. Seismology and Geology, 37(3): 818—828(in Chinese).

The Gulang M 8.0 great earthquake occurred in 1927, many places in Gulang and adjacent areas had suffered destruction in various degrees. So far, divergences exist in the former studies on its seismogenic structure. It is known that clustered small earthquakes often occur in vicinities of fault plane of large earthquake. In this study, the precisely relocated earthquakes which occurred near the earthquake rupture zone between 1985 and 2012 are used, and two strip-shaped zones of clustered small earthquakes are chosen according to the previous studies of the causative structure of this earthquake. Based on the simulated annealing and Gauss-Newtonian nonlinear inversion algorithms, we obtained fault plane parameters of the earthquake such as strike, dip, and location using data of densely concentrated small events. On this condition, rake angles of the fault plane are further inferred from regional tectonic stress parameter. Then we discussed briefly the seismogenic environment and causal mechanism of the earthquake, combined with the results of deep tectonics and surface investigations. The focal fault we inverted locates within the meizoseismal area (intensity Ⅺ)of the Gulang M 8.0 in 1927, suggesting that the focal fault obtained by inversion is possibly the causative structure of this earthquake. Besides, we found a clustered zone of small earthquakes near the south-central part of the main fault, and a fault plane could be derived from them, which we think might be a tensional seismic fault developed on the main fault when the whole earthquake-hit region rotated counterclockwise during the big earthquake.

1 State Geophysics Observatory in Lanzhou, China Earthquake Administration, Lanzhou 730000, China; 2 Lanzhou Base of Institute of Earthquake Prediction, China Earthquake Administration, Lanzhou 730000, China; 3 Earthquake Administration of Gansu Province, Lanzhou 730000, China

1927年古浪发生8级大地震, 此次地震给古浪及邻近地区造成了轻重不等的破坏.对这次地震的发震构造, 前人的研究结果存在较大分歧.本研究根据成丛小震发生在大震断层面附近的原则及参考前人对该地震发震构造的认识, 采用1985年到2012年发生在地震破裂区的精定位地震目录, 选定了2个长条状研究区域, 将模拟退火算法和高斯-牛顿算法结合, 利用小震密集程度求解主震断层面的走向与倾角.在此基础上考虑区域构造应力参数, 给出了已求得的断层面上的滑动角.然后结合已有的深部构造研究结果以及地表考察结果, 简单讨论了此次地震的孕震环境和发震机制.文中反演到的断层①位于此次地震等震线的最高烈度(Ⅺ度)圈内, 表明反演到的震源断层可能就是控制此次地震的发震构造.另外, 首次发现在主干断裂中南部有1个小震成丛区, 也能反演出1个断层, 这可能是地震时震区整体发生了逆时针旋转而在主干断裂之上新发育的张性地震断层.

2018

0.0

... 刘金瑞等(2018)基于LiDAR高精度地形数据, 综合多地点的左旋走滑位错量及不同时代的地貌面年龄数据, 利用蒙特卡洛模拟方法对其开展了研究, 所得结果表明该断裂表现为低滑动速率变化趋势 ...

2008

0.0

刘启元, 陈九辉, 李顺成, 等. 2008. 汶川 M_S8. 0地震: 川西流动地震台阵观测数据的初步分析[J]. 地震地质, 30(3): 584—593.

LIU

Qi-yuan

, CHEN

Jiu-hui

, LI

Shun-cheng

, et al. 2008. The Wenchuan M_S8. 0 earthquake: Preliminary results from the western Sichuan mobile seismic array observations[J]. Seismology and Geology, 30(3): 584—593(in Chinese).

In the western Sichuan(100°～105°E,26°～32°N),a mobile array consisting of 297 broadband seismic stations has been deployed by the State Key Laboratory of Earthquake Dynamics,Institute of Geology,China Earthquake Administration since October of 2006.Until June of 2008,a total of 690 teleseismic events( m b >5.0,30°≤Δ≤90°)have been recorded.The May 12 Wenchuan earthquake( M S 8.0)provides an opportunity to test the western Sichuan array.The preliminary data analysis of the May 12 Wenchuan earthquake and its larger aftershocks has been carried out in this study.Our results show: 1)The event parameters of the May 12 Wenchuan earthquake sequence need to be modified and their location error reaches to 8～24km.A more reasonable estimation of the location of the main shock is possibly at the depth of 19km.2)the wavefield analysis of the Lixian earthquake( M S 5.9)of May 16,2008 manifests that the surface waves of this event are not fully developed,and thus its source depth should not be very shallow.The peak values of the ground-motion velocity on the vertical and horizontal component have an abnormal increase by 4 times and more of the normal attenuation,which is related closely to the faults within the range of 200～250km,when the topography and site effects are not considered.3)The preliminary analysis of the crustal and upper mantle structure beneath the Sichuan basin and the Songpan-Ganzi block manifests that the crust beneath the Sichuan basin thickens along the western direction and its lower crust displays the hard structure.The crustal thickness in the northeast of Chengdu City reaches 46km.The crustal structure beneath the Songpan-Ganzi block has complex lateral variations.The crustal thickness in the Wenchuan earthquake source region reaches 52km.In the depth range of 14～20km,its crust has a complex high-velocity structure with the averaged velocity larger than 4.0km/s.The Wenchuan earthquake should be located within the area with high-velocity medium.In the lower middle crust,a low-velocity layer exists with the S-wave velocity of～3.6km/s,which could provide a relaxed boundary condition for the upper crust movement-deformation.This observation is consistent with the abnormal attenuation of ground motion with the epicenter distance obtained from the wavefield measurements.

State Key Laboratory of Earthquake Dynamics, Institute of Geology, China Earthquake Administration, Beijing 100029, China

2006年10月,中国地震局地质研究所地震动力学国家重点实验室,在中国四川西部(100°～105°E,26°～32°N)布设了由297个宽频带地震台组成的密集流动地震观测台阵。截至2008年6月,川西台阵已记录远震事件( m b >5.0,30°≤Δ≤90°)690个。5.12汶川 M S 8.0地震的发生为检验川西台阵观测系统的观测能力和工作状况提供了机会。文中对5.12汶川地震及其强余震序列观测记录进行了初步分析。结果表明:1)已发布的5.12汶川地震及其强余震参数有必要进一步修正,它们的震中位置可能存在8～24km误差,主震震源深度为19km的估计可能更接近实际情况;2)2008年5月16日理县( M S 5.9)地震的波场分析表明:该地震面波不发育,它不可能是一个浅源地震,地震动速度波场垂直及水平分量峰值的异常增大与断层密切有关,在不考虑地形地貌、土质条件等因素的情况下,震中距200～250km范围内的地震动速度峰值异常增大可达正常衰减的4倍以上;3)利用接收函数方法对四川盆地和松潘-甘孜地块地壳结构的初步分析表明:四川成都北侧地壳厚度达到46km,四川盆地地壳从西向东逐渐增厚,下地壳显示了较为坚硬的特征,松潘-甘孜地块的地壳结构存在十分复杂的横向变化,汶川地震震源区的地壳厚度达到了52km,深度14～20km范围地壳为复杂的高速结构,其S波平均速度超过4.0km/s,汶川地震应位于这个高速介质区内,其中下地壳为平均S波速度约3.6km/s的低速结构,它提供了其上部地壳横向运动的松弛边界条件。这个观察与地震波场观测给出的地震动速度振幅衰减异常增大吻合。

... 同时, 地震台阵观测(刘启元等, 2008 ...

1994

0.0

... 其早期活动表现为挤压逆冲型, 中更新世以来, 其力学性质转变形成以左旋走滑为主(刘小凤等, 1994) ...

... 刘小凤等, 1994)和分段性(何文贵等, 1994)等地质学方面的研究给出了其可靠的活动断裂参数 ...

2001

0.0

... 9地震(荣代潞等, 2001 ...

2018

0.0

... 石富强等(2018)以GPS速度场为约束模拟研究了断层剪切力学性能对区域地壳运动速度场图像的控制作用, 进而在最优模型的基础上分析了当前青藏高原东北缘不同断裂的应力状态, 结果显示中段的金强河-毛毛山-老虎山断裂当前的应力率水平较高 ...

2017

0.0

... 孙赫等(2017)基于InSAR的海原-老虎山-毛毛山断裂带现今的地壳形变特征研究发现毛毛山—老虎山段两侧存在明显差异运动 ...

2015

0.0

太龄雪, 高原, 刘庚, 等. 2015. 利用中国地震科学台阵研究青藏高原东南缘地壳各向异性: 第一期观测资料的剪切波分裂特征[J]. 地球物理学报, 58(11): 4079—4091. doi: DOI: 106038/cjg20151116.

TAI

Ling-xue

, GAO

Yuan

, LIU

Geng

, et al. 2015. Crustal seismic anisotropy in the southeastern margin of Tibetan plateau by ChinaArray data: Shear-wave splitting from temporary observations of the first phase[J]. Chinese Journal of Geophysics, 58(11): 4079—4091(in Chinese).

... 太龄雪等, 2015 ...

2008

0.0

万永革, 沈正康, 刁桂苓, 等. 2008. 利用小震分布和区域应力场确定大震断层面参数方法及其在唐山地震序列中的应用[J]. 地球物理学报, 51(3): 793—804.

WAN

Yong-ge

, SHEN

Zheng-kang

, DIAO

Gui-ling

, et al. 2008. An algorithm of fault parameter determination using distribution of small earthquakes and parameters of regional stress field and its application to Tangshan earthquake sequence[J]. Chinese Journal of Geophysics, 51(3): 793—804(in Chinese).

It is known that clustered small earthquakes often occur in the fault plane vicinities of large earthquakes. Based on the simulated annealing and Gauss-Newtonian nonlinear inversion algorithms, we develop a robust algorithm to estimate fault plane parameters of strong earthquakes such as strike, dip, and location using data of densely populated small events. Rake angle of the fault plane is further inferred from regional tectonic stress parameters. This method can also be employed for determination fault plane parameters of an active fault using data of densely populated small earthquakes.We apply the algorithm to investigate the fault planes of the 1976 Tangshan, Luanxian, and Ninghe earthquakes and the Lulong fault, using precisely relocated earthquakes which occurred near the earthquake rupture zone between 1 April 2002 and 31 May 2006, and obtain the parameters of strike, dip, location, and rake angle of these fault planes. Our estimated fault planes are close to the results of previous studies, testing the validity of our method. In addition, we discover an aligned seismic belt east of the Luanxian seismic zone trending NE-SW, in the form a fracture zone. The faulting parameters of the fracture zone such as the strike, dip and rake are determined accurately. It is still an open question whether the Luanxian and Ninghe faults have ruptured during the Tangshan earthquake sequence, answers to the question await for further multi-disciplinary studies and bear great significance for the understanding of dynamic processes of the Tangshan earthquake sequence.

1 Institute of Disaster Prevention Science and Technology, CEA, Hebei Sanhe 065201,China;2 State Key Laboratory of Earthquake Dynamics, Institute of Geology, CEA, Beijing 100029,China;3 Hebei Seismological Bureau, Shijiazhuang 050021,China

根据成丛小震发生在大震断层面及其附近的原则，将模拟退火算法和高斯-牛顿算法结合，给出了利用小震密集程度求解主震断层面走向、倾角、位置及其误差的稳健估计方法，在此基础上考虑区域构造应力参数，给出了估计在已求得的断层面上的滑动角的方法.该方法还可用于小震活跃地区活断层走向、倾角和滑动角的确定.将这种方法用于唐山地震序列，采用2002年4月1日至2006年5月31日发生在地震破裂区的精定位地震目录，求得了唐山地震、滦县地震、宁河及卢龙断裂带的断层面走向、倾角、位置及滑动角参数.与前人给出的断层面解进行比较，发现利用小震精定位资料和区域构造应力场得到的结果与前人采用其他资料和方法得到的结果近似，验证了这种方法的有效性.另外，本研究首次发现滦县地震区东部的小震呈北东-南西向条带状成丛发生，可精确刻画为一条断裂带，较为精确地确定了此断层的走向、倾角和滑动角.该断裂及宁河断裂在唐山地震序列发生时是否破裂需要运用其他资料进行验证.

... 基于一定的合理假定——地震断层错动方向与局部应力场在该断层面上作用的剪切应力方向一致, 万永革等(2008)给出了断层滑动角的估计方法: 设构造应力场P轴的走向为#cod#x003c6 ...

2001

0.0

1992

0.0

... 其基本思路是寻求一个平面, 使所有小地震的震源位置到这个平面距离的平方和最小(王鸣等, 1992) ...

2003

0.0

... 目前, 该方法已在地震构造研究中得到了广泛应用(杨智娴等, 2003 ...

2017

0.0

... 张艺等, 2017)具有台站分布相对密集、台间距小且分布相对均匀的特点, 可进一步弥补固定监测的不足, 近年来也在中国大陆广泛开展观测 ...

2002

0.0

张国民, 汪素云, 李丽, 等. 2002. 中国大陆地震震源深度及其构造含义[J]. 科学通报, 47(9): 663—668.

ZHANG

Guo-min

, WANG

Su-yun

, LI

, et al. 2002. The focal depths and tectonic implication of continental earthquakes in China[J]. Chinese Science Bulletin, 47(9): 663—668(in Chinese).

对中国大陆地震的震源深度资料作了系统研究. 震源深度的研究, 对于探索地震孕育和发生的深部环境, 地震能量集结、释放的活动构造背景, 以及地壳内部构造变形及其力学属性等都有非常重要的意义. 以1970年1月~2000年5月期间中国大陆M L ≥2.0级并给出深度的31282次1和2类精度的浅源地震为基础, 研究了深度分布特征, 并采用网格滑动平均方法, 统计了网格内地震的平均深度. 结果表明, 中国大陆平均深度为(16±7)km, 东部地区为(13±6)km, 西部为(18±8)km, 东部比西部平均偏浅5 km. 我国大陆地震深度最大的地区是新疆西南部地区, 即塔里木地块的西端和西南缘. 震源深度与构造分区的关系密切, 青藏活动地块震源深度平均为(33±12) km. 新疆活动地块为(21±10) km, 华北为(14±7) km; 东北为(11±5) km; 华南为(10±4) km. 完整地块边界上的地震较深, 其中最明显的是塔里木盆地的西南缘、北缘; 准噶尔盆地的南边缘, 阿拉善地块的南边缘; 鄂尔多斯地块的东、西两侧以及四川盆地的西边缘. 在新生性的破裂带上地震偏浅, 如滇西南地震带及张渤地震带. 另外, 还根据我国震源深度分布特征, 讨论了壳幔(主要是地壳)力学行为、变形属性和破坏方式.

... 震源深度是探讨地震孕育和发生的深部环境、地壳变形特性及其力学性质、属性以及圈层构造等诸多大陆动力学问题的重要参数(张国民等, 2002) ...

2006

0.0

... 周民都, 2006), 空间任意点的速度值均利用线性插值求得 ...

2005

0.0

朱艾斓, 徐锡伟, 胡平, 等. 2005. 首都圈地区小震重新定位及其在地震构造研究中的应用[J]. 地质论评, 51(3): 268—274.

ZHU

Ai-lan

, XU

Xi-wei

, HU

Ping

, et al. 2005. Relocation of small earthquakes in Beijing area and its implication to seismotectonics[J]. Geological Review, 51(3): 268—274(in Chinese).

使用双差地震定位法对首都圈地区39°～4 1°N,115°～118°E范围内1980～2 0 0 0年的2 0 98个小震进行了重新定位,定位均方根残差从重新定位前的1.4 s降到0 .32 s。重新定位后,地震活动多集中分布于北东与北西向断裂的交汇处,或密集成北东与北西向线性分布,与已知活动断裂具有密切的关系。在顺义与延怀盆地一带揭示出几条高角度北西向隐伏活动断裂,长度在10～2 0 km间。小震活动显示的构造信息表明,北西向构造是重要的发震构造,在现今构造变形和地震孕育、发生中,与北东向构造起着同样重要的作用。同时,重定位震源深度分布在东西方向上显示出明显的不均匀性,推测是地壳变形和构造活动强弱在横向变化的一种反映。

... 朱艾斓等, 2005 ...

2002

0.0

... 1 双差定位方法地球内部断裂带的几何结构最初是由地震活动性来揭示的(Schaff et al ...

2002

0.0

... 双差算法通过在各台站同时记录到的2个相邻事件的观测与理论计算走时差的残差(即双差)来确定其相对位置, 可消除共同模式的误差, 尤其是与速度结构横向变化以及台站接收有关的误差, 无须对台站进行校正和准确估计走时即可大幅度提高其相对定位精度(Waldhauser et al ...