1998年以来伽师地震(<em> M</em><sub>W</sub>≥6.0)应力相互作用与强震活动的关系

引用本文

周云, 潘正洋, 王卫民, 何建坤, 王洵, 李国辉. 1998年以来伽师地震( M_W≥6.0)应力相互作用与强震活动的关系 [J]. 地震地质, 2021,43(2): 280-296.
ZHOU Yun, PAN Zheng-yang, WANG Wei-min, HE Jian-kun, WANG Xun, LI Guo-hui. RELATIONSHIP BETWEEN STRESS INTERACTION AND STRONG EARTHQUAKE ACTIVITY OF JIASHI EARTHQUAKES ( M_W≥6.0)SINCE 1998 [J]. SEISMOLOGY AND GEOLOGY, 2021,43(2): 280-296. 复制到剪切板

DOI:10.3969/j.issn.0253-4967.2021.02.002
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1998年以来伽师地震( M_W≥6.0)应力相互作用与强震活动的关系

周云^1,²⁾, 潘正洋³⁾, 王卫民^2),^*, 何建坤²⁾, 王洵²⁾, 李国辉³⁾

1)中国地震局地球物理研究所, 北京 100081

2)中国科学院青藏高原研究所, 大陆碰撞与高原隆升重点实验室, 北京 100101

3)中国地震局地震预测研究所, 北京 100036

*通讯作者: 王卫民, 1971年生, 副研究员, 主要从事地震学研究, E-mail: wangwm@itpcas.ac.cn。

〔作者简介〕周云, 男, 1986年生, 2017年于中国科学院青藏高原研究所获构造地质学专业博士学位, 助理研究员, 主要从事GPS地震学研究, E-mail: zhouyun@cea-igp.ac.cn。

收稿日期: 2020-09-30 修回日期: 2020-11-25

基金项目: 国家自然科学基金(41904050)、中国地震局地球物理研究所基本科研业务专项(DQJB19B33)、中国科学院 “十三五”信息化建设专项项目(XXH13505-06)和中国地震局2021年度震情跟踪定向工作任务(2021020101)共同资助

摘要

新疆伽师地区位于南天山、塔里木盆地和帕米尔3个构造系统的交接部位, 20世纪末—21世纪初该区在短时间内发生了一系列强震。地震应力触发理论认为, 地震之间存在相互联系。文中反演了1998年和2003年2次伽师地震的震源特征, 重建了断层破裂模型; 之后基于黏弹性松弛理论, 计算了2次地震与2020年 M_W6.0地震的相互应力作用, 并研究三者之间的触发关系。结果表明, 1998年地震导致2003年地震发震断层西段的应力增加, 东段应力卸载, 使得2003年地震震源处附近的应力增加了0.01~1MPa, 前者对后者具有明显的触发作用; 前2个地震导致2020年地震发震断层东段的应力增加, 但震中位置处增加的应力≤0.006MPa, 不具有明显的触发作用, 2020年地震的发生主要由其他因素导致, 可能为构造运动加载或以前大地震黏弹性触发所致。在相互触发关系中, 震后黏弹性松弛产生的作用不明显, 同震应力阶变的作用占主导地位。文中结果对于认识伽师地区地震的发生机理和规律具有一定的意义。

关键词: 伽师地震; 应力触发; 黏弹性松弛

中图分类号:P315.72⁺7 文献标志码:A 文章编号:0253-4967(2021)02-0280-17

RELATIONSHIP BETWEEN STRESS INTERACTION AND STRONG EARTHQUAKE ACTIVITY OF JIASHI EARTHQUAKES ( M_W≥6.0)SINCE 1998

ZHOU Yun^1,²⁾, PAN Zheng-yang³⁾, WANG Wei-min²⁾, HE Jian-kun²⁾, WANG Xun²⁾, LI Guo-hui³⁾

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

2)Key Laboratory of Continental Collision and Plateau Uplift, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100101, China

3)Institute of Earthquake Forecasting, China Earthquake Administration, Beijing 100036, China

Abstract

Jiashi seismic region of Xinjiang is located at the junction of South Tianshan, Tarim Basin and Pamir. From January 1997 to March 2003, a series of strong earthquakes occurred in Jiashi area, Xinjiang. In particular, since January 21, 1997, 7 earthquakes with M_S>6 have occurred in the area in just 4 months, which is extremely rare in China and in the world. According to the theory of seismic stress triggering, earthquakes are interrelated with each other. When an earthquake occurs, it will regulate the stress state of its surrounding active faults, thus triggering or inhibiting the seismic risk of surrounding potential faults. Also, the viscoelastic relaxation theory believes that the rheological action of the hot lower crust and mantle will transfer the coseismic stress field changes of the lower crust and upper mantle to the upper crust seismogenic layer in a period ranging from years to hundreds of years after the earthquake. This in turn affects the mechanical properties of the fault.
We invert the focal characteristics of the two Jiashi earthquakes in 1998 and 2003, reconstruct the fault rupture model, and calculate the interaction stress between the two earthquakes and the M_W6.0 earthquake in 2020 based on the viscoelastic relaxation theory to study the triggering relationship among the three earthquakes. We use a viscoelastic layered semi-infinite space model(PSGRN/PSCMP program)to estimate the changes of fault stress caused by coseismic and post seismic deformation. At the same time, we study the influence of different model parameters, including viscosity coefficient, receiving fault parameters and earth medium model parameters, on the calculation results.
The results show that: 1)The 1998 earthquake is a typical sinistral strike-slip earthquake, with fault strike of 57°, dip angle of 81° and the focal depth of 11.5km. The 2003 earthquake is a thrust strike-slip type earthquake with focal depth of 15.2km, the seismogenic fault is a northward low dip angle reverse fault and the main rupture direction of the earthquake is SE, the strike angle is 293° and dip angle is 20°. According to the calculation of fault dip angle, the deepest rupture caused by two seismogenic faults is less than 20km; 2)The 1998 earthquake led to the increase of stress in the western section of the 2003 earthquake fault and the unloading of stress in the eastern section, which increased the stress in the vicinity of the epicenter of the 2003 earthquake by 0.01~1MPa, showing an obvious triggering effect. The first two earthquakes resulted in the increase of stress in the eastern section of the 2020 earthquake fault, but the increase of stress at the epicenter was not more than 0.006MPa, which did not have an obvious triggering effect. This earthquake was mainly caused by other factors, possibly including the tectonic loading or viscoelastic triggering of previous big earthquakes; 3)Considering that there are many factors affecting the distribution of Coulomb stress on the fault, we calculated the stress distribution with different parameters, and the results show that the change of parameters has no obvious effect on the results. In the mutual triggering relationship between the earthquakes, the effect of viscoelastic relaxation after earthquake is not obvious, and the effect of coseismic stress step change is dominant. This may be due to the fact that the fractures caused by the two earthquakes are concentrated in the shallow part, and the coseismic stress in the deep part is relatively small, so the viscoelastic relaxation effect is not obvious. Our stress results are in good agreement with the aftershock distribution obtained by previous relocation methods. The results show that after a long-term stress evolution, the stress loading of the eastern segment of the 2003 earthquake fault is still more than 0.01MPa, so the seismic risk monitoring of this segment should be strengthened. Our results have certain significance for understanding the mechanism and regular pattern of earthquake occurrence in Jiashi area.

Keyword: Jiashi earthquake; stress triggering; viscoelastic relaxation

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0 引言

据中国地震台网中心正式测定, 2020年1月19日在新疆喀什地区伽师县发生M_S6.4地震(下文简称2020年地震), 震源深度为16km。根据USGS地震目录可知, 本次地震是继1996— 1998年一系列地震以及2003年M_W6.3地震(下文简称2003年地震)以来, 发生在伽师地区的又一次M_W> 6的地震事件。基于InSAR资料得到的发震断层模型, 结合破裂运动学特征推测, 这次伽师地震的发震构造是柯坪塔格褶皱带山前出露的柯坪塔格逆断裂(李成龙等, 2020)。伽师地区强震活动频繁, 与所处的大地构造环境密切相关。该区位于天山、帕米尔和塔里木块体3大构造的接触部位, 新生代以来, 受印度-欧亚板块远程碰撞作用的影响, 天山造山带重新活动并再次隆升, 成为欧亚大陆内部规模最大的再生造山带(Tapponnier et al., 1977; Avouac et al., 1993)。同时, 天山造山带夹持在古老而稳定的准噶尔地块和塔里木地块之间, 在持续隆升的同时向两侧扩展, 向S逆冲于塔里木地块之上, 在山前和盆地北缘形成了逆冲断层和大规模褶皱带(张培震等, 2003), 这导致伽师地区成为世界范围内破坏性地震频发、致灾程度严重的强震活动区。

地震应力触发理论认为, 当一个地震发生后, 它将调节周边活动断裂的应力状态, 进而触发或抑制周边潜在断裂的地震危险性(Deng et al., 1997; Lin et al., 2004)。这种调节作用包括弹性同震应力阶变和震后黏弹性松弛导致的应力场变化。在早期研究中, 人们普遍采用弹性半空间位错模型研究大地震与后续地震之间的应力触发关系。如1992年美国加州M_W7.3 Landers地震, King等(1994)计算发现地震使距震中30km处Big Bear地区的同震库仑应力值增加了0.3MPa, 进而触发了随后的M_W6.3地震; 针对1857年Fort Tejon大地震的研究发现, 1857— 1907年间的13次南加州5.5级以上的地震中, 至少有11次与1857年的地震有应力触发关系(Harris et al., 1996)。然而, 仅用同震库仑应力难以解释所有的地震触发作用, 这是由于岩石圈的下地壳和上地幔并非是完全弹性而是黏弹性的, 在震后较长的时间里(几十a甚至几百a)黏滞松弛效应可将应力传递到孕震层, 从而改变断层的应力状态(Pollitz, 1992; Lorenzo-Martí n et al., 2006)。如对1992年M_W7.3 Landers地震和1999年M_S7.1 Hector Mine地震的研究表明, 如果仅考虑同震应力的作用, Hector Mine地震位于Landers地震的应力影响区(Parsons et al., 2000); 但如果同时考虑同震应力和震后黏弹性效应, 则可认为Landers地震触发了后续地震(Freed et al., 2001)。基于黏弹性层状介质模型, 沈正康等(2003)模拟了1937年以来发生在东昆仑断裂带上的5个M> 7地震断层错动导致的应力演化过程, 结果表明前面4个地震对2001年可可西里M_W7.8地震有触发作用。对红河断裂带库仑应力变化的研究发现, 1833年发生的嵩明M8.0地震至今仍然影响着红河断裂带的地震活动(尹凤玲等, 2017)。这些研究结果均表明了考虑黏弹性应力松弛过程在估计地震危险性及分析地震应力触发时的重要性。因此, 在计算地震导致的长期应力场变化时, 同震应力和震后黏弹性效应都不可忽视。

1998年以来, 伽师地区发生了3次M_W> 6的地震, 这些地震相互之间的距离均< 50km(图 1)。那么, 这些地震之间是否也有着相互触发关系?如果有, 同震应力阶变和震后黏弹性松弛, 哪个发挥了主要作用?为了解决这一问题, 本文首先利用地震波形资料, 反演了前2次地震的震源机制与破裂过程; 然后基于更符合实际的分层黏弹性地球介质模型和得到的破裂滑动分布结果, 采用已有的研究方法(Wang et al., 2006)计算了1998年和2003年2次地震对伽师地区造成的应力场变化及其对2020年地震造成的影响, 以研究三者的相互触发作用。

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图 1 伽师地区历史地震分布图
a F₁为2003年2月24日 M_W6.3地震的发震断裂; F₂为2020年1月19日M_W6.0地震的发震断裂, 隶属于柯坪塔格逆断裂; 1996年和1997年3次地震的震中位置来自USGS, 1998年和2003年地震的震中位置来自赵翠萍(2006)的重定位结果, 2020年地震的震中位置来自冉慧敏等(2020)的重定位结果。 b 研究区域(红色方框)与周边主要构造的位置关系Fig. 1 The distribution map of historical earthquakes of Jiashi area.

1 地震震源特征

为了能够提供后续黏弹性应力计算中所需的断裂滑动分布, 我们利用远场地震波形资料反演了1998年8月27日和2003年2月24日2次M> 6地震的震源特征。首先, 通过剪切位错点源模型反演获得震源机制解。震源机制解反演需求解震源深度、滑动角、节面走向、倾角与时间函数。根据反演得到的2个节平面, 结合当地的地质构造背景确定震源破裂面的走向。基于从IRIS下载的地震波形记录, 采用赵翠萍(2006)的重定位结果作为震中位置, 选择信噪比较高且方位角覆盖比较均匀的远场(震中距范围为30° < Δ < 90° )P波垂向波形记录进行反演。反演结果显示, 1998年地震的震源深度为11.5km, 节面1和节面2的走向、倾角和滑动角分别为57° 、 81° 、 -9° 和148° 、 87° 、 -171° 。参考余震重定位结果(赵翠萍, 2006), 选择节面1为断层破裂面。该地震的发震断层面近直立, 是典型的左旋走滑断裂, 其矩张量类似于赵翠萍(2006)给出的走向55° 、倾角84° 和滑动角-4° 的反演结果。

震源机制解显示, 2003年地震的震源深度为15.2km, 节面1和节面2的走向、倾角和滑动角分别为78° 、 73° 、 56° 和293° 、 20° 、 124° 。考虑到该地震有一定的逆冲分量, 而节面1的倾角比较大, 同时地震考察结果表明发震断层是一条近EW走向且向N倾的逆断层(沈军等, 2006), 因此选择节面2为断层破裂面。将震源机制反演计算的理论地震图与观测波形资料进行拟合, 结果显示波形的相关性较好(图 2)。表1为2次地震的震源机制解。

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图 2 1998年和2003年2次伽师地震的震源机制解
采用下半球投影, 同时给出了点源模型的P波垂向位移理论图(红线)与资料(黑线)的拟合情况。图形下方给出了2组节面解(图a中, λ 、 δ 、 θ 、 h分别表示断层滑动角、断层倾角、断层走向、震源深度)和点源模型的震源时间函数(b)Fig. 2 Focal mechanisms of two Jiashi earthquakes in 1998 and 2003.

表1 1998年和2003年2次M_W> 6地震震源及断层参数 Table 1 Source and fault parameters of the two earthquakes(M_W> 6)in 1998 and 2003

根据有限断层反演方法(王卫民等, 2008; 周云等, 2015), 结合2次地震的点源模型反演结果, 选用沿走向长51km、沿倾向宽18km的断层面, 并将其划分成3km× 2km的153个子断层, 使用P波和SH波数据进行断层面时空破裂过程反演。计算同震位移响应采用基于分层介质模型的广义反射透射系数矩阵方法(谢小碧等, 1989), 震源区的地壳结构模型获取自Crust2.0。反演使用非线性最优化的模拟退火技术, 目标函数由采用波形相关系数与同震位移矢量差的归一化加权叠加定义。图 3 为反演得到的2次伽师地震的断层滑动分布。结果显示, 2次地震均为M_W6.3地震, 1998年地震的破裂较为集中, 最大滑动量为60cm, 标量地震矩为3.22× 10¹⁸N· m, 该结果与赵翠萍(2006)的滑动分布结果类似: 最大滑动量为63cm, 呈双侧破裂特征。 2003年地震的破裂较为分散, 最大滑动量为56cm, 标量地震矩为3.15× 10¹⁸N· m。其中2003年的地震以SE向单侧破裂为主, 这与沈军等(2006)野外考察得出的该地震为N倾逆冲断层自NW向SE由深至浅破裂的结果一致。

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	图 3 1998年和2003年2次伽师地震断层破裂滑动分布 a 1998年8月27日M_W6.3地震断层滑动分布; b 2003年2月24日M_W6.3地震断层滑动分布Fig. 3 Fault slip distribution of Jiashi earthquakes in 1998 and 2003.

2 应力计算方法及参数

2.1 研究方法

地震发生后, 同震和震后应力调整均会导致断层面上库仑应力变化。根据库仑破裂准则, 接收断层的静态库仑应力变化可以表示为

$Δ CFS = Δ τ + μ Δ σ$ (1)

式中, Δ CFS为断层面上库仑应力的变化量, Δ τ 为断层面上剪切应力的变化量, μ 为断层的有效摩擦系数, Δ σ 为断层面上正应力的变化量, 以拉伸为正。在不同的研究中, μ 的取值也有所不同, 但不会改变库仑应力变化的整体分布形态(张国宏等, 2008; 万永革等, 2009)。在本文的计算中, 取μ =0.4。因本次研究主要计算2003年和2020年地震发震断层面受到的影响, 参考前文反演结果和王卫民等^①(①http://www.itpcas.ac.cnkycgyjcg/202001/t20200122_5494135.html。)的结果, 选取地下15km为计算库仑应力变化的深度。

在计算库仑应力时, 本文使用了德国波茨坦地球科学中心(GFZ)Wang等(2006)开发的PSGRN/PSCMP程序。该软件主要包括2个部分, PSGRN用来计算给定分层模型下基本位错源的时变格林函数, 所得结果为第2个程序PSCMP的基础数据, 之后通过线性叠加方法对点位错进行计算, 得到同震和震后形变的结果。计算时重力和分层介质影响都被考虑在内, 通过使用基于反混淆技术的快速傅里叶变换得到格林函数, 保证了结果的稳定性。

2.2 模型参数

本文的模型计算范围为(38° ~41° N, 76° ~79° E)。在进行格林函数计算时, 需要先建立地下速度介质模型。选择何玉梅等(2001)以及赵翠萍(2006)研究伽师地震群采用的速度模型(表2), 该模型综合了上地壳速度反演结果和刘启元等(2000)利用接收函数得到的深部速度结构。石耀霖等(2008)认为, 塔里木块体中地壳的等效黏滞系数为10²¹~10²³Pa· s, 下地壳的黏滞系数为10²¹~10²²Pa· s。本模型中弹性层厚度为16km, 黏弹性中下地壳采用Burgers体模型。中地壳的稳态黏滞系数取1.0× 10²²Pa· s, 下地壳稳态黏滞系数取2.0× 10²¹Pa· s, 瞬时与稳态黏滞系数一般差1个数量级(Ryder et al., 2011)。地幔黏滞系数比下地壳大得多, 取为2.0× 10²²Pa· s。

表2 伽师地区岩石圈地层介质模型 Table 2 Layered lithosphere medium model in Jiashi region

2003年伽师M_W6.3地震的发震断层(图 1 中的F₁)为隐伏断裂, 未能很好地确定其断层参数, 因此在设置接收断层参数时, 我们参考了该地震的震源机制解。 2020年M_W6.0地震的发震断层(图 1 中的F₂)为柯坪塔格逆断裂的一部分, 我们根据周德敏(2013)的结果给出了断层滑动参数, 如表3所示。

表3 2003年和2020年地震的发震断层参数 Table 3 Fault parameters of earthquakes in 2003 and 2020

3 计算结果

3.1 对发震断层应力的影响

为了进一步研究1998年以来的3次M_W≥ 6地震之间的相互关系, 我们计算了同震及黏弹性松弛导致的2003年2月24日M_W6.3地震的发震断层F₁和2020年1月19日M_W6.0地震的发震断层F₂上的库仑应力变化, 如图 4 所示。图 4a为1998年地震导致的发震断层上的同震库仑应力变化, 可以看到本次地震使断层F₁西段的应力值增加, 东段的应力值减小, 变化量基本都超过了0.01MPa; 同时, 该地震使F₂西段应力减小, 东段应力增加。经过4.5a的调整后, 图 4b显示应力分布和应力值并没有明显的变化, 2003年地震位于应力增加区范围内, 应力增加值为0.01~1MPa, 达到了0.04MPa。图 4c为在原有的应力基础上增加了2003年地震同震应力的情况, 本次地震明显调整了断层F₁的应力状态, 卸载了F₁西段的应力, 增加了东段的应力, 同时也扩张了断层F₂东段的应力增强区。黄媛等(2006)重定位后的余震主要集中在断层的应力增强区, 同时余震的分布也支持发震断层N倾的结论。在2020年M_W6.0地震发生之前, 经过近20a的震后调整, 断层面上应力变化不大, 2020年地震位于应力增强区内, 应力增加值介于0.003~0.006MPa之间, 为0.005MPa。

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	图 4 发震断层上的库仑应力变化 a 1998年地震的同震应力; b 2003年地震发生之前的应力分布; c 2003年地震发生之后的应力分布, 黑色小圆圈为2003年2月24日— 2003年4月30日M> 3.5的余震(黄媛等, 2006); d 2020年地震发生之前的应力分布Fig. 4 Coulomb stress change on the seismogenic faults.

3.2 改变黏滞系数对断层库仑应力分布的影响

前文的计算结果显示, 震后调整对应力分布的作用并不明显。在计算震后的应力场演化时, 地层黏滞系数的选取对结果可能会有一定影响。我们主要参考了石耀霖等(2008)给出的塔里木盆地的黏滞系数参数, 由于发震区位于盆山交会处, 而山体与盆地的黏滞系数一般并不相等, 因此, 本文另外选取了一组黏滞性参数进行对比。由于研究区域西南天山地壳和地幔黏滞系数尚无较好的约束, 故参考了青藏高原的参数数值。石耀霖等(2008)认为青藏高原下地壳等效黏滞系数较低, 约为10¹⁹~10²⁰Pa· s, 因此将中地壳和下地壳的黏滞系数调低为5.0× 10²⁰Pa· s和5.0× 10¹⁹Pa· s, 上地幔黏滞系数设为5.0× 10²⁰Pa· s, 计算结果如图 5 所示。可以看到, 与图 4 相比, 经4.5a的调整后, 1998年地震导致F₁西段的应力有所减弱; 在2020年M_W6.0地震发生之前, 经过近20a的震后调节, F₁中段的应力有所减小。震后下地壳和上地幔中的同震应力变化, 向上传递到上地壳孕震层的过程中, 黏滞系数越低, 应力传递越快(Shan et al., 2013)。而天山的下地壳和上地幔黏滞系数可能比青藏高原更大(卢双疆等, 2013), 因此在本次伽师地震应力计算中, 改变黏滞系数对应力分布并无明显影响。

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图 5 调整黏滞系数后发震断层上的库仑应力变化
a 1998年地震的同震应力; b 2003年地震发生之前的应力分布; c 2003年地震发生之后的应力分布, 黑色小圆圈为2003年2月24日— 4月30日M> 3.5的余震(黄媛等, 2006); d 2020年地震发生之前的应力分布Fig. 5 Coulomb stress change on the seismogenic faults after adjusting viscosity coefficient.

3.3 改变接收断层参数对断层库仑应力分布的影响

由于未能很好地界定发震断层F₁和F₂的断层参数, 而不同的接收断层参数会对应力分布的计算结果产生影响, 因此, 我们参考了前人的反演结果对断层参数进行了设置。前人利用CDSN的数字波形资料反演得到了2003年地震的震源机制解(走向306° 、倾角50° 、滑动角129° )(徐锡伟等, 2006); 而根据InSAR反演获得的2020年地震的断层走向为270° 、倾角为15° 、滑动角为85° (李成龙等, 2020)。以3.2节中的参数作为地壳和地幔的黏滞系数, 计算结果如图 6 所示。从图中可知, 1998年地震加载了F₁西段的应力, 2003年地震震源处的应力增加> 0.01MPa, 同时卸载了东段的应力。 2003年地震卸载了F₁西段的应力, 加载了东段的应力, 与余震分布的相关性较好; 同时, 加载了F₂东段的应力, 在2020年地震震源处的应力改变≤ 0.01MPa。总体而言, 与图 4 和图 5 相比, 接收断层参数的改变对应力分布的影响不大。

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	图 6 调整断层参数后发震断层上库仑应力变化 a 1998年地震的同震应力; b 2003年地震发生之前的应力分布; c 2003年地震发生之后的应力分布, 黑色小圆圈为2003年2月24日— 4月30日M> 3.5的余震(黄媛等, 2006); d 2020年地震发生之前的应力分布Fig. 6 Coulomb stress change on the seismogenic faults after adjusting fault parameter.

3.4 改变地球模型参数对断层库仑应力分布的影响

不同的地球模型参数会对应力分布的计算结果产生影响。我们参考了周德敏(2013)在研究柯坪-阿克苏地震带时使用的介质模型。由于文中只给出了P波速度, 故根据波速比1.73计算S波速度, 得到的速度模型如表4所示。计算应力时采用3.2节中的黏滞系数。

表4 柯坪-阿克苏岩石圈的地层介质模型 Table 4 Layered lithosphere medium model in Aksu region

计算结果如图 7 所示。相比于图 4、图 5 和图 6, 更改地球模型参数没有改变应力的整体分布。 1998年地震使得2003年地震震源处的库仑应力增加值> 0.01MPa; 前2次地震对2020年地震震源处的应力影响介于0.006~0.01MPa之间。震后的黏弹性松弛作用依然不明显。

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图 7 调整地球模型参数后发震断层上的库仑应力变化
a 1998年地震的同震应力; b 2003年地震发生之前的应力分布; c 2003年地震发生之后的应力分布, 黑色小圆圈为2003年2月24日— 4月30日M> 3.5的余震(黄媛等, 2006); d 2020年地震发生前的应力分布Fig. 7 Coulomb stress change on the seismogenic faults after adjusting Earth model parameter.

4 讨论

当断层面上的库仑应力增量> 0.01MPa, 就有可能会触发地震, 即认为0.01MPa为 “ 触发阈值” (King et al., 1994)。本文的计算结果表明, 1998年M_W6.3地震对断层F₁在2003年地震震中所在区域附近产生的应力增量为0.01~1MPa, 超过了触发阈值, 表明两者之间存在触发作用。王琼等(2007)认为1998年地震对2003年地震没有触发作用, 产生的应力增加近似为0。两者的差异可能是断层破裂模型不同所导致的。王琼等(2007)基于断层长度估算公式, 根据地震震级构建了破裂模型, 并认为滑动是均匀分布的。这种处理方法计算的应力结果对较远的断层影响较小。然而2003年地震的发震断层F₁距离1998年的地震震中很近(图 4), 这样得到的应力结果误差可能比较大。本文根据基于地震波形反演得到的破裂滑动分布计算库仑应力, 可相对更真实地反映断层的应力状态。本文的计算结果表明, 2020年地震也位于库仑应力增加区内, 但应力增加值为0.003~0.006MPa, < 0.01MPa, 说明前2个地震对后一个地震并没有明显的触发作用, 本次地震的发生可能为其他因素所导致, 如区域应力加载或者以前大地震的黏弹性触发等。同时计算结果也显示, 经历长期应力演化后, 2003年地震的发震断层F₁东段的应力加载依然> 0.01MPa, 因此应加强对该段的地震危险性监测工作。

影响断层上库仑应力分布的因素较多, 例如地球模型参数、接收断层参数和地壳黏弹性系数等。本文考虑了不同的影响因素, 对应力的分布情况进行了研究。结果显示, 断层面上的应力在经过长时间的黏弹性松弛后并没有发生明显的变化, 这可能是由于地震震级较小导致的。从反演结果来看, 前2次地震都为M_W6.3地震。根据断层倾角的计算结果, 2个发震断层的破裂最大深度均≤ 20km, 且破裂主要发生在浅部, 最大滑动量≤ 60cm, 在断层模型深部几乎没有明显破裂(图 3), 说明这2个地震对下地壳和地幔的应力扰动有限。黏弹性松弛理论认为, 热的下地壳和地幔的流变作用, 使得在震后的数年至数百年时间里, 下地壳和上地幔的同震应力场变化传递到上地壳的孕震层中, 进而影响断层的力学性质(Pollitz, 1992; Marsan et al., 2003; Freed et al., 2007)。由于2个地震在深部产生的同震应力较小, 故黏弹性松弛作用也不明显。因此, 在对后续地震的影响中, 由同震产生的应力阶变依然占据主导地位。

1997年1月— 2003年3月, 新疆伽师地区发生了一系列强震活动。尤其是自1997年1月21日起, 在短短4个月的时间内, 该区域发生了7次M_S≥ 6.0的大地震, 这种现象在中国大陆甚至世界范围内都是极为罕见的。张竹琪等(2008)计算了1997年强震间的库仑应力作用, 认为这些地震之间存在触发关系, 且伽师地震的正断层活动在地震发生中起到了重要的促进作用, 这在一定程度上解释了伽师地震群的发震机制。然而, 依然有一些问题没有得到很好解决, 例如: 为什么是短时间内发生多次零散的5级、 6级地震, 而不是发生1次7级地震使得能量一次性全部释放出来?根据应力触发理论, 这些地震是否是一个早期特大地震(比如1902年阿图什M8¼地震)导致的库仑应力变化后的连续触发?黏弹性应力转化在这一过程中起到了多大的作用?以上这些问题有待于未来更进一步的研究。

5 结论

本文基于远场波形反演, 重新构建了1998年8月27日与2003年2月24日2次M_W6.3地震的破裂滑动分布, 并基于震后黏弹性松弛的方法计算了2次地震与2020年M_W6.0地震相互之间的应力作用, 得到的结论如下:

(1)1998年地震为典型的左旋走滑型地震, 震源深度为11.5km, 破裂比较集中, 断层的走向为57° , 倾角为81° ; 2003年地震为逆冲兼走滑型地震, 震源深度为15.2km, 发震断层为一条向N低角度倾斜的逆断裂, 断层的走向为293° , 倾角为20° , 地震以SE单方向破裂为主。

(2)1998年地震经4.5a的应力调整之后, 导致2003年地震发震断层的西部应力增加, 东部应力卸载, 使得2003年地震震源处附近应力增加了0.01~1MPa, 前者对后者具有明显的触发作用。前2个地震导致2020年地震的发震断层东部应力增加, 但震中位置处的应力增加≤ 0.006MPa, 因此对2020年地震不具有明显的触发作用, 2020年地震的发生主要由其他因素所致。在这一过程中, 震后黏弹性松弛作用并不明显, 同震应力阶变占据了主导地位。

致谢本文利用IRIS地震波形资料进行计算; 图件由GMT软件生成; 使用汪荣江老师的PSGRN/PSCMP程序计算库仑应力。在此一并表示感谢!

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2001

0.0

何玉梅, 郑天愉, 单新建. 2001. 1996年3月19日新疆阿图什6. 9级地震: 单侧破裂过程[J]. 地球物理学报, 44(4): 510—519.

Yu-mei

, ZHENG

Tian-yu

, SHAN

Xin-jian

. 2001. The 1996 Artux, Xinjiang, earthquake: A unilateral rupture event[J]. Chinese Journal of Geophysics, 44(4): 510—519(in Chinese).

Using the broadband P wave records of the Global Digital Seismograph Network（GDSN） and the adaptive hybrid global search algorith,we investigate the rupture process of the 19 March,1996 Artux,Xinjiang,earthquake(M S=6.9）. Slip vectors,risetime and rupture time for a finite fault are obtained and their errors is estimated by introducing a random weight method. Aftershock data,field geology and seismic investigations are applied to constrain the fault plane. This event occurred in the west part of the Kalpin fault zone and is a unilateral rupture thrust event with a small strike slip component. The fault plane has a stricke of 252° and a dip of 30°. The rupture duration is 15s and the focal depth is 13km. We conclude that the inferred slip distribution contains two major slip sources. A sub event with a slip amplitude of 0.3m and a risetime of 0.8s is located at the hypocenter. The maximum slip amplitude of 1.0m is associated with a 3.5s risetime subevent located to the east of the first major slip source. The distance between the two major slip sources is about 25km,and corresponds with the 30km difference between the instrumental and macroseismic epicenters.

Institute of Geology and Geophysics,Chinese Academy of Science,Beijing 100101,China

结合已有的地质、余震分布及地震宏观考察资料,使用全球数字地震台网(GDSN)宽频带P波数据,利用波形拟合和有限断层的全局混合反演方法研究了1996年3月19日新疆阿图什地震的震源破裂时空过程.结果表明,这次地震是发生在柯坪断裂带的哈帕雷克断层上的一次具有逆倾和较小走滑分量的由西向东单侧破裂事件.断层面的走向为252°,倾角30°,震源深度为13km,震源持续时间为15s.破裂面上的滑动分布主要由两部分构成:初始破裂0.3m对应较小上升时间0.8s;最大滑动尺度1.0m则位于沿破裂方向离初始点约25km处,相应的上升时间为3.5s.由于微观震中是指震源开始破裂的地方,而宏观震中则代表地面破坏最严重的区域,我们的反演结果解释了其他研究者得出的微观震中与宏观震中相距约30km的结论.

... 选择何玉梅等(2001)以及赵翠萍(2006)研究伽师地震群采用的速度模型(表2), 该模型综合了上地壳速度反演结果和刘启元等(2000)利用接收函数得到的深部速度结构 ...

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)重定位后的余震主要集中在断层的应力增强区, 同时余震的分布也支持发震断层N倾的结论 ...

2020

0.0

... 基于InSAR资料得到的发震断层模型, 结合破裂运动学特征推测, 这次伽师地震的发震构造是柯坪塔格褶皱带山前出露的柯坪塔格逆断裂(李成龙等, 2020) ...

... (李成龙等, 2020) ...

2000

0.0

刘启元, 陈九辉, 李顺成, 等. 2000. 新疆伽师强震群区三维地壳上地幔S波速度结构及其地震成因的探讨[J]. 地球物理学报, 43(3): 356—365.

LIU

Qi-yuan

, CHEN

Jiu-hui

, LI

Shun-cheng

, et al. 2000. Passive seismic experiment in Xingjiang Jiashi strong earthquake region and discussion on its seismic genesis[J]. Chinese Journal of Geophysics, 43(3): 356—365(in Chinese).

From January 21 to April 16 of 1997, seven strong earthquakes took place in Jiashi region of Xinjiang, China. This Phenomenon was never happened in Chinese continent since earthquakes were able to be recorded by instruments. To investigate the deep structure environment of the Jiashi strong earthquake sequence, a portable broadband seismic array of 30 stations was set up in Jiashi region over about 11,000 km 2 . The portable array crossed the Tarim basin and the Tian Shan fold belt. The distance between stations is about 5-10 km. The frequency bandwidth of our observation system is 0.05--20 Hz. The 3--D S-wave velocity structure down to 100 km beneath the army was obtained by using the teleseismic receiver function migration and its nonlinear inversion techniques （Liu etc. 1996）. The following conclusions can be obtained from our observations: l) The Moho depth is about 4052 kin on the side of the Tarim basin and becomes 60-76 km deep on the side close to the Tien Shan. The crustal thickness beneath the fold belt nearby the south Tien Shan is much thicker than that of the Tarim basin and the obvious tectonic deformation exists in the crust. 2) The north boundary of the Tarim basin is clearly laterally inhomogeneous. The relationship of the contact deformation between Tarim and Tien Shan reveals the compressional movement to the NNW direction. The topography of the Moho discontinuity beneath our array has obvious correlation with the arctuate tectonics on the surface. The arctuate fold formation is closely related with the deep structure and the compression by the Tarim basin. 3) The Jiashi strong earthquake sequence mainly occurred over the gradient zone of the crust--mantle boundary. The genesis of the Jiashi earthquake sequence probably related to the activity of the conceal faults nearby the sources. This may result from the inhomogeneous deformation at the north boundary and the current tectonic movement of the Tarim basin. 4) The Jiashi strong earthquake sequence mainly occurred in the upper crust beneath the fold belt with a lower shear module. This could be a reason why the stress drop of these events is much smaller than common. All of these demonstrate that the Jiashi earthquake sequence genesis is related not only to the current tectonic movement of the Tarim basin, but also to the deep structure. This will need to be investigated further by the numerical stress modeling.

Institute of Geology, China Seismological Bureau, Beijing 100029, China

１９９７年１月２１日至４月１６日（北京时间）新疆伽师地区连续发生了７次６级以上强烈地震．为了深入研究该强震群形成的构造背景，我们在伽师强震群区及其邻域大约１１０００ｋｍ２的范围内布设了由３０台宽频带数字地震仪组成的流动地震台阵，台站的间距约５－１０ｋｍ．利用远震体波接收函数的叠加偏移分析及其非线性反演技术，研究了台阵下方０－１００ｋｍ深度范围内地壳、上地幔的三维Ｓ波速度结构．结果表明：１)Ｍｏｈｏ界面的深度在塔里木盆地一侧为４０—５２ｋｍ，而在靠近天山一侧的褶皱变形区为６０—７６ｋｍ，南天山山前折皱变形区的地壳厚度明显增大，地壳内部产生了明显变形；２)塔里木盆地北缘存在明显的不均匀性，塔里木盆地与天山之间的接触变形关系显示了塔里木盆地向北北西方向的挤压作用，台阵下方壳幔界面的地形与地表的地貌特征有较好的相关性，山前弧形褶皱带的形成与地下深部结构及挤压作用有关；３)伽师强震群分布在壳幔界面梯度带的上方，该震群的成因可能与震源区附近的隐伏断裂活动有关；４)由于震源处于褶皱变形区的地壳上部，相应的剪切模量较小，这可能是伽师强震群应力降明显偏低的...

2013

0.0

... 而天山的下地壳和上地幔黏滞系数可能比青藏高原更大(卢双疆等, 2013), 因此在本次伽师地震应力计算中, 改变黏滞系数对应力分布并无明显影响 ...

2020

0.0

2006

0.0

沈军, 陈建波, 王翠, 等. 2006. 2003年2月24日新疆巴楚-伽师6. 8级地震发震构造[J]. 地震地质, 28(2): 205—212.

SHEN

Jun

, CHEN

Jian-bo

, WANG

Cui

, et al. 2006. The seismogenic tectonics of the M_S6. 8 Bachu-Jiashi, Xinjiang earthquake in Feb. 24, 2003[J]. Seismology and Geology, 28(2): 205—212(in Chinese).

The M S 6.8 Bachu-Jiashi earthquake of Feb.24, 2003 occurred in the western Tarim Basin and is possibly the continuation of the Jiashi strong earthquake swarms in 1997-1998. However, its focal mechanism and rupture process are different from that of the Jiashi strong earthquake swarms, according to our preliminary study on its seismic tectonics with geomorphologic information from satellite images, the deep structures from the petroleum seismic exploration, the macro damage and isoseismic features from field investigation, the relocation of the epicenters of the aftershocks, and the regional seismic tectonics from both deep and surface tectonics. The occurrence of the M S 6.8 Bachu-Jiashi earthquake is closely related with the revealed reverse fault on the Maigaiti slope belt between the Bachu uplift and Kashi depression in western Tarim Basin. The sites of the ground fissures found in the field fit with the revealed reverse fault. Isoseismal features are also corresponding to the rupture direction of the fault. These evidences indicate that the M S 6.8 Bachu-Jiashi earthquake is the result of the southward rupturing from deep to shallow along a north-dipping reverse fault in Tarim Basin. This reverse fault is possibly the result of the propagation of the thrust fault-fold system named Kalpintag thrust belt in the front of Tianshan.

1. Earthquake Administration of Xinjiang Uygur Autonomous Region, Urumqi 830011, China; 2. Resource and Environment College of Xinjiang University, Urumqi 830046, China

2003年2月24日发生在新疆塔里木盆地的巴楚-伽师6.8级地震可能是1997-1998年伽师强震群的继续,但其震源机制解、破裂过程与1997-1998年的强震群有一定的差别。从地震重新定位的结果看,巴楚-伽师6.8级地震与塔西南坳陷东侧麦盖提斜坡带上发育的一组NWW向隐伏逆断层有关,地震宏观考察①所发现的与构造变形有关的地裂缝也与这一隐伏断层带的位置相吻合,等震线形态与隐伏断层带的走向一致,极震区的形态与断层的破裂方向基本一致。这些均表明这次地震是盆地内一条近EW向北倾逆断层自NW向SE由深至浅破裂的结果。

... 考虑到该地震有一定的逆冲分量, 而节面1的倾角比较大, 同时地震考察结果表明发震断层是一条近EW走向且向N倾的逆断层(沈军等, 2006), 因此选择节面2为断层破裂面 ...

... 其中2003年的地震以SE向单侧破裂为主, 这与沈军等(2006)野外考察得出的该地震为N倾逆冲断层自NW向SE由深至浅破裂的结果一致 ...

2003

0.0

沈正康, 万永革, 甘卫军, 等. 2003. 东昆仑活动断裂带大地震之间的黏弹性应力触发研究[J]. 地球物理学报, 46(6): 786—795.

SHEN

Zheng-kang

, WAN

Yong-ge

, GAN

Wei-jun

, et al. 2003. Viscoelastic triggering between large earthquakes along the east Kunlun fault system[J]. Chinese Journal of Geophysics, 46(6): 786—795(in Chinese).

We study the stress transfer and triggering of large earthquakes along the East Kunlun fault system, northern Tibet. Five M≥7 earthquakes occurred along the fault zone during the past 70 years are considered: the M7.5 Huashi Canyon earthquake, the 1963 MS 7.1 Dulan earthquake, the 1973 MS7.3 Manyi earthquake, the 1997 MS7.5 Manyi earthquake, and the 2001 MW7.8 Kokoxili earthquake. We simulate the stress evolution process produced by seismic dislocations in layered viscoelastic media, and calculate the Coulomb failure stress change on the fault plane of each subsequent earthquake. The result shows that the Coulomb failure stress on the fault plane of the Kokoxili earthquake was increased by the previous 4 earthquakes, and theviscoelastic relaxation gradually enhanced the Coulomb failure stress field as time elapsed. By evaluating the Coulomb failure stress changes produced by the coseismic rupture and viscoelastic relaxation of the 4 preceding large earthquakes, we find that the Coulomb failure stress changes produced by the viscoelastic relaxation are much more significant than that produced by the coseismic deformation in 3 of the 4 earthquakes. The stress field simulation indicates that after the Kokoxili earthquake the Coulomb failure stress in the XidatanDongdatan segment (between the Kokoxili and Dulan segments) of the East Kunlun fault is increased as much as 0.05～0.10 MPa, implying increased probability of seismic hazard in this region.

1 Institute of Geology, China Seismological Bureau, Beijing, 100029, China 2 Dept of Earth and Space Sciences，University of California, Los Angeles, CA 900951567, USA 3 College of Disaster Prevention Technique, Yanjiao, Beijing, 101601, China 4 Seismological Lab, University of Nevada, Reno, NV 89577, USA

对青藏高原北部东昆仑破裂带大地震之间的应力转移和断层相互作用进行研究. 考虑1937年以来沿此破裂带发生的5个M≥7的地震：1937年M7.5花石峡地震，1963年MS7.1都兰地震，1973年MS7.3玛尼地震，1997年MW7.5玛尼地震和2001年MW7.8可可西里地震，模拟了黏弹性成层介质中地震断层错动产生的应力演化过程，并计算了在后续地震破裂面上产生的库仑破裂应力变化. 结果表明，前面4个地震均造成2001年可可西里地震断层面上库仑破裂应力的增加，并且中地壳和下地壳的黏弹性松弛效应使得库仑破裂应力场随着时间的推移而逐渐加强. 在计算过程中定量估计了可可西里地震发生时前面4个地震同震形变和黏弹性松弛导致可可西里地震破裂面上库仑破裂应力变化之间的比值，发现前3个地震由黏弹性松弛造成的变化远远大于同震形变所造成的变化. 可可西里地震之后应力场的模拟表明东昆仑断层中段的东大滩－西大滩断层段（位于可可西里地震破裂以东及都兰地震以西）的库仑破裂应力显著增加，变化值达0.05～0.1 MPa，预示这一地区地震危险性的增加.

2008

0.0

... 石耀霖等(2008)认为, 塔里木块体中地壳的等效黏滞系数为10²¹~10²³Pa#cod#x000b7 ...

2009

0.0

... 万永革等, 2009) ...

2007

0.0

... 王琼等(2007)认为1998年地震对2003年地震没有触发作用, 产生的应力增加近似为0 ...

... 王琼等(2007)基于断层长度估算公式, 根据地震震级构建了破裂模型, 并认为滑动是均匀分布的 ...

2008

0.0

王卫民, 赵连锋, 李娟, 等. 2008. 四川汶川8. 0级地震震源过程[J]. 地球物理学报, 51(5): 1403—1410.

WANG

Wei-min

, ZHAO

Lian-feng

, LI

Juan

, et al. 2008. Rupture process of the M_S8. 0 Wenchuan earthquake of Sichuan, China[J]. Chinese Journal of Geophysics, 51(5): 1403—1410(in Chinese).

On 12 May, 2008 the great Wenchuan earthquake with magnitude Ms8.0 occurs on the Longmen Shan belt, which is located at the eastern margin of the Tibetan Plateau and northwestern Sichuan region of China. The strong shaking of the Wenchuan earthquake causes great disasters to life and property, and severe geologic damages, e.g. landslides and cracks to dams are inflicted. Based on the geologic studies and the surface rupture investigation, we constructed a more realistic double-listric finite-fault model, and reconstructed the source rupture process by combined inverting the teleseismic waveforms and local coseismic displacement. Results show that the Wenchuan earthquake is characterized mainly by thrust motion with right-lateral strike slip also, and two faults-Yingxiu-Beichuan fault and Guanxian-Jiangyou fault participated simultaneously during the rupture process. The estimated maximum slip on the fault can reach up to 12~12.5 m, and the distribution of slip on the faults with high magnitude can be projected to Yingxiu and Beichuan county which are severely damaged. The average strike-slip motion is a little larger than the slip motion, which is coincident with the deformation observation along the Longmen Shan tectonic region. The long-time regional stress accumulation, the composition of this region and special tectonic structure might be the reason for this great Wenchuan earthquake with recurrence interval of thousand years.

1 Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100085, China 2 Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China

2008年5月12日在青藏高原与四川盆地交界的龙门山山脉发生了 M s 8.0级强烈地震，引发山体滑坡等地质灾害,造成了巨大的人员伤亡和经济损失.本文利用远场体波波形记录结合近场同震位移数据，根据地质资料和地震形成的地表破裂轨迹，构造了一个双“铲状”有限地震断层模型，利用反演技术重建地震的破裂过程.结果显示汶川大地震主要是沿龙门山构造带的映秀—北川断裂和灌县—江油断裂发生的逆冲兼右旋走滑破裂事件.断层面上的滑动分布显示两个高滑动区先后发生在地震破坏最为严重的映秀和北川地区，最大滑动量高达1200～1250 cm，且破裂过程也显示一定的复杂性.地震破裂的平均走滑量略大于平均倾滑量，与多种观测资料获得的震前龙门山断裂带构造变形相一致，推断是由于长期区域应力场作用和龙门山地区特殊的物质组成和结构孕育了这次千年尺度的强烈地震.

... 根据有限断层反演方法(王卫民等, 2008 ...

1989

0.0

谢小碧, 姚振兴. 1989. 计算分层介质中位错点源静态位移场的广义反射、透射系数矩阵和离散波数方法[J]. 地球物理学报, 32(3): 270—280.

XIE

Xiao-bi

, YAO

Zhen-xing

. 1989. A generalized reflection-transmition coefficient matrix method to calculate static displacement field of a stratified half-space by dislocation source[J]. Chinese Journal of Geophysics, 32(3): 270—280(in Chinese).

The generalized reflection-transmition coefficient matrix method for calculating synthetc se-ismograms is extended to deal with the static problems,from which a method to calculate the static displacement field of a stratified half space by dislocation source is developed.The advantages of the original reflection-transmition coefficient matrix method are retained.By comparing the numerical results with the analytical solutions,it is shown that this is an effective method for the investigation of the static deformation produced by seismic faulting process.From careful analysis we find there are both similarities and differences between the wave propagation and static problems.

Institute of Geophysics, Acadcmia Sinica, Beijing

本文将计算合成地震图的广义反射、透射系数矩阵和离散波数方法应用于静态问题,给出了分层介质中位错点源产生的静态位移场的计算方法。该方法保留了反射、透射矩阵方法的原有优点,通过将数值结果与解析解的对比表明,该方法具有较高的数值精度,可用于研究地震断层活动造成的地表形变。

... 计算同震位移响应采用基于分层介质模型的广义反射透射系数矩阵方法(谢小碧等, 1989), 震源区的地壳结构模型获取自Crust2 ...

2006

0.0

徐锡伟, 张先康, 冉勇康, 等. 2006. 南天山地区巴楚-伽师地震( M_S6. 8)发震构造初步研究[J]. 地震地质, 28(2): 161—178.

Xi-wei

, ZHANG

Xian-kang

, RAN

Yong-kang

, et al. 2006. The preliminary study on seismotectonics of the 2003 AD Bachu-jiashi earthquake( M_S6. 8), southern Tian Shan[J]. Seismology and Geology, 28(2): 161—178(in Chinese).

Owing to strong and permanent Cenozoic re-orogenic processing, a lot of EW-striking active thrusts and folds have been developed in Tian Shan, resulting in crustal shortening in NS direction. There also exist NW-striking transform-like strike-slip faults that cut the Tian Shan and accommodate uneven crustal shortening larger in the west and smaller in the east. The seismogenic structures in and around the Tian Shan mainly include EW-striking thrust ramps or blind thrusts and NW-striking transform-like strike-slip faults. The 2003 AD Bachu-Jiashi earthquake is located at south of the Kalpintag nappe. A NE-trending deep seismic reflection profile about 50km long across the epicenter has been conducted after the earthquake. From this reflection profile four blind faults are identified. Together with earthquake relocation, these identified blind faults are used in the paper to interpret the seismogenic structures of the 1997 AD Jiashi strong earthquake swarm and 2003 AD Bachu-Jiashi earthquake. The 1997 AD Jiashi strong earthquakes were generated mainly by a NW-striking buried transform-like strike-slip fault, while the 2003 AD Bachu-jiashi earthquake by blind thrusts in front of the Kalpintag nappe.

1. Institute of Geology, China Earthquake Administration, Beijing 100029, China; 2. Geophysical Exploration Center, China Earthquake Administration, Zhengzhou 450003, China; 3. Institute of Crustal Dynamics, China Earthquake Administration, Beijing 100085, China; 4. Earthquake Administration of Xinjiang Uygur Autonomous Region, Urumqi 830011, China

新生代期间强烈而持久的再生造山作用,在天山地区形成了大量近EW向逆断裂-褶皱带,引起地壳强烈缩短,穿插有NW向“类转换断层”,显示出天山地区近NS向不均匀的构造挤压作用;区域上地震构造主要为近EW向逆断裂-褶皱带或盲逆断层,其次为NW向“类转换断层”。巴楚-伽师地震区位于南天山柯坪塔格推覆构造系以南,NE向跨越极震区、长约50km的深地震反射探测表明,1997年伽师强震群的发震构造推测为NW向隐伏“类转换断层”,2003年巴楚-伽师地震( M S 6.8)的发震构造为柯坪塔格推覆构造系南缘尚未出露地表的近EW向盲逆断层系。

... )(徐锡伟等, 2006) ...

2017

0.0

... 0地震至今仍然影响着红河断裂带的地震活动(尹凤玲等, 2017) ...

2008

0.0

张国宏, 单新建, 李卫东. 2008. 汶川 M_S8. 0地震库仑破裂应力变化及断层危险性初步研究[J]. 地震地质, 30(4): 935—944.

ZHANG

Guo-hong

, SHAN

Xin-jian

, LI

Wei-dong

. 2008. The Coulomb failure stress change associated with the M_S8. 0 Wenchuan earthquake and the risk prediction of its surrounding faults[J]. Seismology and Geology, 30(4): 935—944(in Chinese).

Using the focal mechanisms and slip distribution model of the M S 8.0 Wenchuan earthquake,we inverted the co-seismic Coulomb failure stress change.The inverted Coulomb stress change based on Chen J's slip distribution model shows that about 83%of its aftershocks lie in regions where the Coulomb stress increased by 0.01MPa,given the receiver fault' strike/dip/rake as 204?/56?/98? respectively.In contrast,the distribution of aftershocks is sparse in areas where the inverted Coulomb stress change is decreased by 0.01MPa.From this we can tell that aftershocks are abundant where the Coulomb stress change rose by more than 0.01MPa,and aftershocks are sparse where the Coulomb stress dropped by a similar amount.This study and the forerunner,Ma et al (2005),demonstrate that even when the source geometry and slip distribution are complex,Coulomb stress change is correlated with the distribution of aftershocks.And its main characteristic is that for most of the region in the northern wall of the fault the Coulomb stress dropped by 0.01MPa and for most of the region in the southern wall of the fault,it increased by 0.01MPa.The tendency of change of the Coulomb stress field is progressed to the direction of N-E and S-W.At last,we calculated the Coulomb stress change on most of the existing faults based on Deng's active fault data.The results show that the Coulomb stress change on several strike-slip faults is decreased by about 0.01MPa,including Maerkang Fault,southeast Chengdu thrust fault,Huya Fault,Min Jiang Fault,west Qinling north-edge fault and Qinling north-edge fault.This means these faults may be less dangerous in future earthquakes.There are several strike-slip faults on which the Coulomb stress change are increased by about 0.01MPa,including eastern Kunlun Fault,northern part of Chengdu thrust fault,Wenxian Fault,and western part of west Qinling north-edge fault.These results are consistent with that of Tom Parsons et al.What brings contradiction is that when comes to Xianshuihe Fault,our results show an increase by about 0.01MPa in the middle part of Xianshuihe Fault,at longitude 101.2皌o 102癊 and latitude 30皌o 31.04癗.The Coulomb stress change in most part of Xianshuihe Fault is decreased,which means the Xianshuihe Fault system has a potential seismic risk lower that it had before the M S 8.0 Wenchuan earthquake.

1. State Key Laboratory of Earthquake Dynamics, Institute of Geology, China Earthquake Administration, Beijing 100029, China; 2. Spatial Informatics Institute, Henan University of Technology, Zhengzhou 450001, China

利用四川省汶川 M S 8.0地震的震源机制解及滑动分布模型,反演了由汶川地震造成的同震库仑破裂应力变化;从余震效应与断层相互作用的角度对库仑破裂应力变化进行了分析。结果显示:基于滑动分布模型反演的库仑破裂应力变化能较好地反映与余震分布的对应关系,以最大余震断层面参数(走向/倾角/滑动角:204°/56°/98°)为接收断层,反演结果最佳,83%M>4的余震均发生于库仑应力增加约0.01MPa的区域;库仑破裂应力变化的主要特征为断层北盘大部分区域为库仑破裂应力下降区,断层南盘主要为增加区,断层两端均显示库仑破裂应力变化增加,且分别沿NE和SW两个方向发展。最后,基于活断层分布模型,计算由此次地震造成的已存断层面上的库仑破裂应力变化,结果显示多条左旋走滑断裂库仑破裂应力变化值增加。

... 的取值也有所不同, 但不会改变库仑应力变化的整体分布形态(张国宏等, 2008 ...

2003

0.0

... 同时, 天山造山带夹持在古老而稳定的准噶尔地块和塔里木地块之间, 在持续隆升的同时向两侧扩展, 向S逆冲于塔里木地块之上, 在山前和盆地北缘形成了逆冲断层和大规模褶皱带(张培震等, 2003), 这导致伽师地区成为世界范围内破坏性地震频发、致灾程度严重的强震活动区 ...

2008

0.0

... 张竹琪等(2008)计算了1997年强震间的库仑应力作用, 认为这些地震之间存在触发关系, 且伽师地震的正断层活动在地震发生中起到了重要的促进作用, 这在一定程度上解释了伽师地震群的发震机制 ...

2006

0.0

... 基于从IRIS下载的地震波形记录, 采用赵翠萍(2006)的重定位结果作为震中位置, 选择信噪比较高且方位角覆盖比较均匀的远场(震中距范围为30#cod#x000b0 ...

... 参考余震重定位结果(赵翠萍, 2006), 选择节面1为断层破裂面 ...

... 该地震的发震断层面近直立, 是典型的左旋走滑断裂, 其矩张量类似于赵翠萍(2006)给出的走向55#cod#x000b0 ...

... m, 该结果与赵翠萍(2006)的滑动分布结果类似: 最大滑动量为63cm, 呈双侧破裂特征 ...

2013

0.0

... 0地震的发震断层(图 1 中的F₂)为柯坪塔格逆断裂的一部分, 我们根据周德敏(2013)的结果给出了断层滑动参数, 如表3所示 ...

... 我们参考了周德敏(2013)在研究柯坪-阿克苏地震带时使用的介质模型 ...

2015

0.0

周云, 王卫民, 熊林, 等. 2015. 2014年2月12日 M_W6. 9于田地震震源破裂过程及对周围断层的应力影响[J]. 地球物理学报, 58(1): 184—193.

ZHOU

Yun

, WANG

Wei-min

, XIONG

Lin

, et al. 2015. Rupture process of 12 February 2014, Yutian M_W6. 9 earthquake and stress change on nearby faults[J]. Chinese Journal of Geophysics, 58(1): 184—193(in Chinese).

On February 12 2014, an M s 7.3 earthquake hit Yutian, Xinjiang, the epicenter is at the intersection of Karakax fault and Gonggacuo fault. Earthquake triggering theory indicates that Coulomb stress on nearby faults will change because of crustal coseismic slip after earthquake, and it will affect earthquake potential risk. In this paper, we estimate focal mechanism and rupture process with far field seismic wave data, and calculate coseismic stress change on nearby faults around epicenter. The purpose is to discuss Coulomb stress change and seismic potential hazard on these faults caused by Yutian earthquake. After the earthquake, we download seismic far field wave data of which epicenter is between 30°to 90° from IRIS. We select 27 high SNR(signal to noise ratio) seismic record to make theoretical seismogram. We use generalized ray theory to get synthetic seismic wave map, and sub fault parameter inverse process is based on simulated annealing algorithms. In the way of changing fault parameter to fit actual and synthetic wave form, optimum solution of every sub fault is found. Based on fault rupture inversion model and infinite elastic half space theory, we calculate Coulomb stress change on nearby faults caused by the earthquake. The inversion results show that source depth of earthquake is 10 km, dip angle is 71.9°, largest coseismic displacement is 210 cm. Seismic moment is 2.91×10 19 N·m, the main seismic energy is released in former 10 second. Aftershocks are mainly distributed in three regions: north Pulu fault, east Karakax fault and centre Gonggacuo fault. Stress increased significantly on western segment of Altyn fault, central part of Pulu fault, eastern segment of Karakax fault and central segment of Gonggacuo fault. Among them the largest stress change is 0.05 MPa on Karakax fault and 0.04 MPa on Gonggacuo fault. Former research shows that, Coulomb stress change caused by earthquake larger than 0.01 MPa will dramatically increase seismic risk on faults. In our research, stress change on Pulu fault, Gonggacuo fault and Karakax fault exceed triggering threshold, so all these three faults have seismic risk. In the near future seismic potential hazard on these faults should be closely monitored. In the past 6 years, 3 moderately strong earthquakes happen in the study area, epicenters migrate from Gonggacuo fault to Altyn fault, from southwest to northeast. Though stress change on Altyn fault is much lower, in consideration of 9 mm·a -1 slip rate, seismic risk on Altyn fault should cause enough attention.

Key Laboratory of Continental Collision and Plateau Uplift, Institute of Tibetan Plateau Research, CAS, Beijing 100101, China

2014年2月12日,在新疆于田县发生了里氏7.3级地震.在该地震震中附近,前人研究证明发育了大量规模不同的活动断层(如康西瓦断裂与贡嘎错断裂等).根据地震触发理论,地震发生后因地壳同震变形会导致其周边不同性质断裂破裂应力发生变化,进而影响其地震的潜在危险性.本文利用地震远场波形记录,反演了该地震滑动模型.之后,根据弹性无限半空间位错理论,计算了该地震在近场范围内活动断裂上的同震应力变化.其目的在于讨论于田地震引起的附近断裂上的库仑应力变化以及这些活动断裂可能潜在的地震危险性.在地震发生后,从国际地震学联合会(IRIS)地震数据中心,下载了震中距离介于30°~90°的地震远场波形记录,为保证台站方位角分布均匀,从中挑选了27个不同方位角的高信噪比地震记录参与理论地震图的生成和波形反演过程.我们采用广义射线理论计算生成远场理论地震波形数据.每个子断层参数的反演则利用基于全局化反演的快速模拟退火反演方法.在有限断层反演过程中,我们采用了强调波形拟合的相关误差函数作为待反演的目标函数,拟合的断层参数使目标函数为最小.之后,根据弹性无限半空间位错理论,以库仑破裂准则为基础,结合反演得到的地震震源机制解和地震位错模型,计算该地震引起的近场断层面上库仑应力的变化.由远场波形计算结果可以看到,于田地震的震源深度为10 km,地震断层的倾角约71.9°,破裂面上最大的同震位移达到210 cm,以左旋走滑为主并具有正倾滑分量,地震能量主要在前15 s内释放.由此得到该地震的地震矩为2.91×10 19 N·m,地震震级为 M w 6.9.于田地震引发的余震,大致分布在三个区域内:普鲁断裂北部、康西瓦断裂东部和贡嘎错断裂中部.弹性应力计算结果表明,于田地震导致阿尔金断裂西段、普鲁断裂中段、康西瓦断裂东段和贡嘎错断裂中段的静态库仑应力明显增加,其中以康西瓦断裂东段和贡嘎错断裂中段应力增量为最大,分别达到了0.05 MPa和0.04 MPa.大量研究证明,当地震所导致的库仑应力变化大于0.01 MPa时将具有明显的地震触发作用.根据本文结果,2014年于田 M w 6.9地震使普鲁断裂、贡嘎错断裂和康西瓦断裂上的库仑应力增量均超过了触发阈值,具有被触发出地震的潜在危险.因此,在以后的地震学研究中,应加强对该三条断裂地震危险性的研究和监测.此外,近6年以来,研究区域发生了3次6级以上的地震.这些地震均沿着贡嘎错断裂,由南西向北东迁移,逐步靠近阿尔金断裂,并且逐渐由正倾滑型地震转变为走滑型地震.阿尔金断裂的走滑速率达到了9 mm·a -1 ,所以,尽管本次地震导致的阿尔金断裂库仑应力增量小于0.01 MPa,阿尔金的地震危险性也应该加强监测.

... 周云等, 2015), 结合2次地震的点源模型反演结果, 选用沿走向长51km、沿倾向宽18km的断层面, 并将其划分成3km#cod#x000D7 ...

1993

0.0

... Avouac et al ...

1997

0.0

... 地震应力触发理论认为, 当一个地震发生后, 它将调节周边活动断裂的应力状态, 进而触发或抑制周边潜在断裂的地震危险性(Deng et al ...

2007

0.0

... Freed et al ...

2001

0.0

... 但如果同时考虑同震应力和震后黏弹性效应, 则可认为Landers地震触发了后续地震(Freed et al ...

1996

0.0

... 5级以上的地震中, 至少有11次与1857年的地震有应力触发关系(Harris et al ...

1994

0.0

... 3 Landers地震, King等(1994)计算发现地震使距震中30km处Big Bear地区的同震库仑应力值增加了0 ...

... (King et al ...

2004

0.0

... Lin et al ...

2006

0.0

... Lorenzo-Mart#cod#x000ed ...

2003

0.0

... Marsan et al ...

2000

0.0

... 1 Hector Mine地震的研究表明, 如果仅考虑同震应力的作用, Hector Mine地震位于Landers地震的应力影响区(Parsons et al ...

1992

0.0

... 然而, 仅用同震库仑应力难以解释所有的地震触发作用, 这是由于岩石圈的下地壳和上地幔并非是完全弹性而是黏弹性的, 在震后较长的时间里(几十a甚至几百a)黏滞松弛效应可将应力传递到孕震层, 从而改变断层的应力状态(Pollitz, 1992 ...

... 黏弹性松弛理论认为, 热的下地壳和地幔的流变作用, 使得在震后的数年至数百年时间里, 下地壳和上地幔的同震应力场变化传递到上地壳的孕震层中, 进而影响断层的力学性质(Pollitz, 1992 ...

2011

0.0

... s, 瞬时与稳态黏滞系数一般差1个数量级(Ryder et al ...

2013

0.0

... 震后下地壳和上地幔中的同震应力变化, 向上传递到上地壳孕震层的过程中, 黏滞系数越低, 应力传递越快(Shan et al ...

1977

0.0

... 该区位于天山、帕米尔和塔里木块体3大构造的接触部位, 新生代以来, 受印度-欧亚板块远程碰撞作用的影响, 天山造山带重新活动并再次隆升, 成为欧亚大陆内部规模最大的再生造山带(Tapponnier et al ...

2006

0.0

... 然后基于更符合实际的分层黏弹性地球介质模型和得到的破裂滑动分布结果, 采用已有的研究方法(Wang et al ...

... 在计算库仑应力时, 本文使用了德国波茨坦地球科学中心(GFZ)Wang等(2006)开发的PSGRN/PSCMP程序 ...