鲜水河断裂带三维变形特征

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赵静, 任金卫, 江在森, 岳冲. 鲜水河断裂带三维变形特征[J]. 地震地质, 2018,40(4): 818-831.
ZHAO Jing, REN Jin-wei, JIANG Zai-sen, Yue Chong. THREE-DIMENSIONAL DEFORMATION CHARACTERISTICS OF THE XIANSHUIHE FAULT ZONE[J]. SEISMOLOGY AND GEOLOGY, 2018,40(4): 818-831. 复制到剪切板

DOI:10.3969/j.issn.0253-4967.2018.04.007
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鲜水河断裂带三维变形特征

赵静^1,², 任金卫³, 江在森³, 岳冲²

1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

2中国地震台网中心, 北京 100045

3中国地震局地震预测重点实验室, 中国地震局地震预测研究所, 北京 100036

〔作者简介〕赵静, 男, 1985年生, 2012年于中国地震局地震预测研究所获固体地球物理学专业硕士学位, 助理研究员, 主要研究方向为GPS数据处理、地壳形变分析和断层闭锁反演, E-mail: zhaozhengjiajia1@126.com。

收稿日期: 2017-11-28

基金项目: 国家自然科学基金(11672258)与中国地震局地震科技星火计划项目(XH16044)共同资助

摘要

为了综合分析讨论鲜水河断裂带的三维运动与变形动态特征和地震危险性, 利用川滇地区1999—2007和2013—2017 2期GPS速度场资料, 反演计算了鲜水河断裂带的闭锁程度和平行与垂直断层的滑动亏损速率动态分布; 利用布设在鲜水河断裂带附近的1980—2017年跨断层短水准资料, 通过计算断层年均变化速率分析了断裂带垂直运动特征。GPS反演结果显示: 1999—2007期鲜水河断裂SE段处于强闭锁状态, 中段闭锁程度逐渐减弱, 到NW段基本为蠕滑状态; 2013—2017期鲜水河断裂SE段滑动亏损积累速率明显减弱, 只有道孚—八美段之间有一小段闭锁较强, NW段依然大部分为蠕滑状态, 只有炉霍SE部一段断层地表至10km深度闭锁稍有增强。水准结果显示: 鲜水河断裂NW段侏倭、格篓、虚墟和沟普场地年均垂直变化速率较大, 断层垂向活动较为活跃; SE段龙灯坝、老乾宁和折多塘场地年均垂直变化速率很小, 断层垂向活动处于闭锁状态; 汶川地震后断层垂向活动变化并不明显。综合分析认为鲜水河断裂SE段的地震危险性较高, 而汶川地震降低了断层滑动亏损和应力应变能积累速率, 可能在一定程度上缓解了鲜水河断裂尤其SE段的地震紧迫性。

关键词: 鲜水河断裂; 断层闭锁程度; 年均垂直变化速率; 三维变形特征

中图分类号:P315.2 文献标志码:A 文章编号:0253-4967(2018)04-0818-14

THREE-DIMENSIONAL DEFORMATION CHARACTERISTICS OF THE XIANSHUIHE FAULT ZONE

ZHAO Jing^1,², REN Jin-wei³, JIANG Zai-sen³, Yue Chong²

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

2)China Earthquake Networks Center, Beijing 100045, China

3)CEA Key Laboratory of Earthquake Prediction, Institute of Earthquake Science,China Earthquake Administration, Beijing 100036, China

Abstract

In order to analyze 3-dimensional movement and deformation characteristics and seismic risk of the Xianshuihe fault zone, we inverted for dynamic fault locking and slip deficit rate of the fault using the GPS horizontal velocity field of 1999-2007 and 2013-2017 in Sichuan-Yunnan region, and calculated annual vertical change rate to analyze the vertical deformation characteristics of the fault using the cross-fault leveling data during 1980-2017 locating on the Xianshuihe fault. The GPS inversion results indicate that in 1999-2007, the southeastern segment of the fault is tightly locked, the middle segment is less locked, and the northwestern segment is basically in creeping state. In 2013-2017, the southeastern segment of the fault is obviously weekly locked, in which only a patch between Daofu-Bamei is locked, and the northwestern segment is still mostly in creeping state, in which only a patch at southeastern Luhuo is slightly locked from surface to 10km depth. The cross-fault leveling data show that annual vertical change rate of the Zhuwo, Gelou, Xuxu and Goupu sites on the northwestern segment is larger, which means vertical movement is relatively active, and annual vertical change rate of the Longdengba, Laoqianning, and Zheduotang sites on the southeastern segment is small, which means the fault is locked, and the vertical movement changes little before and after the Wenchuan earthquake. Combining with the 3-dimensional movement and deformation, seismic activity and Coulomb stress on the Xianshuihe Fault, we consider the seismic risk of the southeastern segment is larger, and the Wenchuan earthquake reduced the far-field sinistral movement and the fault slip deficit rate, which may reduce the stress and strain accumulation rate and relieve the seismic risk of the southeastern segment.

Keyword: the Xianshuihe Fault; fault locking; annual vertical change rate; 3-dimensional deformation characteristics

文章图片

0 引言

鲜水河断裂带是现今青藏高原上活动最剧烈的断裂之一, 是1条位于川滇菱形块体东北边界上的NW走向的左旋走滑断裂带, 其南端分别与安宁河— 则木河— 小江断裂带和龙门山断裂带相接, 构成了川滇菱形块体、巴颜喀拉地块、华南地块的交叉口(方颖等, 2010)。鲜水河断裂带为当今地学研究的热点断裂, 闻学泽(2000)、 Papadimitriou等(2004)和Wen等(2008)对鲜水河断裂带的地震破裂分段特征进行过细致的研究; 冉洪流等(2006)对鲜水河断裂带NW段、周荣军等(2001)对鲜水河断裂带乾宁— 康定段的强震复发间隔进行了研究; Zhang等(2018)对鲜水河断裂带NW段、易桂喜等(2015)对鲜水河断裂带康定段的断层面参数进行了研究; 苏琴等(2012)、李腊月等(2016)利用跨断层短水准和基线结果对鲜水河断裂带断层活动特征进行了分析; 徐晶等(2013)对1893年以来鲜水河断裂带库仑应力演化与区域强震的关系进行了研究; Wang等(2009)、 Jiang等(2015)利用GPS和InSAR数据反演计算了鲜水河断裂NW段的震间滑动速率和鲜水河— 安宁河— 则木河断裂的闭锁程度。综上所述, 有关地震破裂分段、强震复发间隔、断层面参数、断层近场运动、库仑应力演化、震间断层滑动与闭锁等的研究已较为丰富, 但同时利用多期GPS速度场资料和跨断层短水准数据研究鲜水河断裂三维运动变形与闭锁动态特征的相对较少。

自1700年以来, 鲜水河断裂带先后经历了1700— 1816年和1893年至今2个大地震活跃期, 第1个地震活跃期基本造成了整个断裂带的破裂(Wen et al., 2008; 徐晶等, 2013); 第2个地震活跃期中, 断裂带NW段发生了6次M6.7以上地震, 造成了NW段大部分断层段破裂, 而SE段仅发生了1955年折多塘M7.5地震, 破裂长度只有30~35km, 还有多处段落未发生M6.7以上地震(Papadimitriou et al., 2004; Wen et al., 2008; 徐晶等, 2013), 且早期的GPS和InASR数据研究结果表明道孚— 康定之间存在潜在凹凸体(Jiang et al., 2015), 跨断层短水准和基线研究结果表明龙灯坝和老乾宁附近存在强闭锁区(Zhang et al., 2018), 因此鲜水河断裂带尤其是SE段目前的运动变形与闭锁程度分布如何, 发生于龙门山断裂带的2008年汶川M8.0地震对其变形特征和应力应变能积累等产生怎样的影响, 都值得深入研究, 这对于判定鲜水河断裂带目前的地震危险性具有重要意义。本文利用汶川地震前较长时间跨度的1999— 2007期和汶川地震后最新的2013— 2017期GPS水平速度场数据, 采用DEFNODE负位错程序反演计算了鲜水河断裂的闭锁程度和平行与垂直断层的滑动亏损速率动态空间分布; 同时利用鲜水河断裂带附近的1980— 2017年跨断层短水准资料, 采用断层年均变化速率分析了鲜水河断裂带垂直运动和变形规律, 并结合上述三维结果综合分析讨论了鲜水河断裂带不同段落的地震危险性。

1 鲜水河断裂带GPS速度场反演结果

1.1 GPS数据与断层模型设置

本文所用GPS数据包括 “ 中国地壳运动观测网络” 和 “ 中国大陆构造环境监测网络” 在中国大陆进行的1999年、 2001年、 2004年、 2007年、 2013年、 2015年和2017年流动观测数据, 以及截止日期为2017年10月的连续站观测数据。经过数据处理解算得到了1999— 2007期(王敏研究员提供的ITRF参考框架结果)和2013— 2017期(湖北省地震局提供的ITRF参考框架结果)GPS速度场, 然后通过转换得到了相对于华南地块的速度场结果, 其中1999— 2007期GPS速度场有196个测站数据参与反演, 2013— 2017期GPS速度场有362个测站数据参与反演(图1)。

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	图1 研究区域GPS水平运动速度场(相对于华南地块)与跨断层短水准场地分布Fig. 1 The horizontal GPS velocity field(relative to South China Block)and cross￣fault leveling in the study region.

考虑到鲜水河断裂带与安宁河— 则木河— 小江断裂带、龙门山断裂带在青藏高原东缘构成了交叉口(方颖等, 2010; 玄松柏等, 2015), 这3条断裂带之间的运动与变形存在着相互影响, 因此本研究在建立块体和断层系统模型时同时考虑了上述3条断裂带, 将整个研究区域以它们为边界, 划分为川滇地块、巴颜喀拉地块和华南地块(图1)。下面重点介绍依据地震地质等结果对鲜水河断裂带NW段和SE段断面参数进行设置的情况。

(1)鲜水河断裂带NW段断面参数设置

Zhang等(2018)给出了鲜水河断裂带NW段上侏倭、格篓、虚墟、虾拉坨、沟普、老乾宁等场地建站时地质调查确定的断层倾角和通过小震精定位确定的断层倾角(表1), 并将2种结果进行了对比分析, 确定了断层的地震地质属性, 其中格篓场地2种结果的断层倾向并不一致, Zhang等(2018)认为其主断层面应该为通过小震精定位确定的NE倾。因此鲜水河断裂NW段主断层面为NE倾, 且断层倾角很大、断层近直立。另外, 小震精定位结果显示侏倭、虾拉坨和沟普场地在深度10km左右以下, 断层的倾向和倾角可能会发生变化, 其他3个场地处断层面基本为平面, 断层的倾向和倾角不随深度变化。本文依据上述实际地震地质研究资料构建鲜水河断裂带NW段的断层模型, 考虑到本文所用DEFNODE负位错反演程序(Savage et al., 2001; McCaffrey, 2002, 2005, 2007; 赵静等, 2014, 2015)必须要区分断层的上下盘, 且同1条断层的上下盘不能随深度发生改变, 因此将NW段断层断面参数设定为NE∠85° 。Zhang等(2018)的研究成果对本文鲜水河断裂带NW段断层三维结构的设置起到了很好的支持作用。

表1 鲜水河断裂带NW段横跨断层的6个观测场地的部分信息(Zhang et al., 2018) Table1 Some information of the six cross￣fault geodetic sites along the northwestern Xianshuihe fault zone (after Zhang et al., 2018)

另外, 本文还参考了其他一些文献中关于鲜水河断裂带NW段断层倾角的研究结果, 其中Papadimitriou等(2004)和徐晶等(2013)将炉霍、恰叫、道孚、八美段的断层倾角均设置为90° ; 冉洪流等(2006)认为炉霍段的断层倾角为75° 、倡促段的断层倾角为60° ~85° 、松林口— 乾宁段的断层倾角为60° ~80° 。上述参考文献中断层倾角的原始参数, 也基本支持本文将鲜水河断裂NW段断面参数设定为NE∠85° 。

(2)鲜水河断裂带SE段断面参数设置

鲜水河断裂带SE段主要由4条分支断裂组成, 其中雅拉河与折多塘2条断裂均为较短的分支, 可分别看做独立的破裂段, 剩下的为主干断裂色拉哈-磨西断裂(闻学泽, 2000)。鲜水河断裂带SE段深部电性结构研究结果表明, 中上地壳断裂带构造表现出花状构造, 既有倾角陡立并且切穿地壳的深大断裂, 也有倾角稍缓会聚于深大断裂的小断裂(何梅兴等, 2017), 因此雅拉河、折多塘、色拉哈-磨西等断裂可能在深部会聚于1条主干断裂。

表2为根据地质测量方法获得的鲜水河断裂带SE段横跨断层的3个观测场地信息, 结果显示断层结构基本为NE∠70° ~80° 左右。2014年11月22日康定M6.3地震后, 易桂喜等(2015)利用gCAP矩张量反演和地震序列重新定位的方法分析认为, 色拉哈断裂倾角约为82° 、折多塘断裂倾角约为83° 。

表2 鲜水河断裂带南东段横跨断层的3个观测场地的部分信息(四川省地震局提供) Table2 Some information of the three cross￣fault geodetic sites along the southeastern Xianshuihe fault zone(after Sichuan Earthquake Agency)

另外, Papadimitriou等(2004)和徐晶等(2013)将雅拉河与折多塘段的断层倾角设置为75° 、将色拉哈段的断层倾角设置为85° 、将康定与磨西段的断层倾角设置为80° 。本文依据表2实际地质调查结果、地震序列重新定位结果和前人的断层模型设置结果等原始参数, 考虑到方便构建块体和断层模型以进行反演计算, 以及鲜水河断裂SE段倾角小于NW段倾角, 将浅部的花状构造简化为1条主干断裂, 即将雅拉河与折多塘2条分支断裂与主干断裂色拉哈-磨西断裂简化为1条断层, 并将南东段断层断面参数设定为NE∠75° 。

综上所述, 三维断层模型设置中, 为了研究沿倾向方向、不同深度断层闭锁程度的变化特征, 沿着鲜水河断裂走向共设置6条等深线, 由浅至深依次为0.1km、 5km、 10km、 15km、 20km和25km, 为了研究沿走向方向断层闭锁程度的变化特征, 每条等深线上设置11个节点; 北西段断层倾角设置为85° , 南东段断层倾角设置为75° ; 断裂总长度为323km。为了方便读者重复构建出相同的断层面模型, 图2展示了断层三维结构与节点设置。

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	图 2 鲜水河断裂带断层三维结构与节点设置Fig. 2 3￣dimensional structure and node setting on Xianshuihe fault zone.

1.2 最优模型结果

本研究所用DEFNODE负位错反演程序的基本原理和使用方法见参考文献(Savage et al., 2001; McCaffrey, 2002, 2005, 2007; 赵静等, 2014, 2015)。该程序能够利用GPS数据、水准数据、 InSAR数据等通过网格搜索和模拟退火算法, 反演计算块体内部永久应变、块体旋转、块体边界断层闭锁程度等, 其中断层闭锁程度为断层滑动亏损速率与断层长期滑动速率的比值, 比值为0表示断层完全蠕滑, 比值为1表示断层完全闭锁, 比值介于0~1之间, 表示断层存在一定的蠕滑运动, 只是部分闭锁。DEFNODE程序相对于一般的同类型反演程序, 增加了块体内部永久应变的反演, 而块体内部永久应变可以替代震后部分黏弹性松弛作用的影响, 因此该程序可以在震后的相关反演中使用。此外, 该程序可以将断层设置为有一定倾角的曲面, 即沿着走向和倾向断层结构都可以有所变化, 这使得我们可以用该程序来反演研究复杂的断层结构, 这与一般的同类型反演程序相比也有了很大的进展。在使用DEFNODE程序前, 对该程序的反演可靠性和稳定性进行了验证, 结果表明在不同断层倾角条件下反演结果均具有高度可靠性; 权值f对反演结果影响微弱, 反演结果具有很好的稳定性(赵静等, 2013)。

由于华南地块内部应变很小、整体稳定, 因此反演过程中认为其只存在整体旋转运动和由于断层闭锁而产生的弹性应变, 不存在内部永久应变; 而川滇地块和巴颜喀拉地块由于内部变形明显(熊维等, 2015), 认为其存在整体旋转运动、内部永久应变和由于断层闭锁而产生的弹性应变。大地震引起的震后变形包括震后余滑和黏弹性松弛等作用, 震后早期的形变可以用发生在断层面上的蠕滑加以模拟, 而黏弹性松弛的贡献不大; 但黏弹性松弛衰减速率较慢, 震后影响时间长(王丽凤等, 2013)。相关研究表明震后余滑作用的影响时间一般约3~4a, 因此本文所用的2013— 2017期GPS速度场受汶川震后余滑作用的影响已经很弱, 而是主要受震后黏弹性松弛作用的影响。由于震后黏弹性松弛作用在块体变形上的表现是使块体产生内部应变, 因此本文反演过程中将黏弹性松弛作用以块体内部永久应变来简单代替, 这使得2013— 2017期GPS速度场的拟合残差中应该还包含了部分震后应力松弛作用的影响。

通过多次计算得到的最优模型中, 1999— 2007期观测值数量为392, 自由度为283, $χ_{n}^{2} = 0.99;$ 2013— 2017期观测值数量为724, 自由度为615, $χ_{n}^{2} = 1.06 。$ 2期最优模型拟合的残差分布如图3所示。图3a结果表明, 除了安宁河断裂东边几个测点、川滇地块西边界几个测点、巴颜喀拉块体西端几个测点速度残差值稍大以外, 其他位置测点的速度残差值较小, 大部分处在误差范围之内(赵静等, 2015)。图3b结果表明, 除了安宁河断裂东边几个测点、川滇地块西边界几个测点、龙门山断裂中北段附近部分测点速度残差值较大以外, 其他位置测点的速度残差值较小, 这与赵静等(2015)中2009— 2013期GPS速度场反演结果的残差分布较为一致。以上结果表明2期最优模型拟合效果都较好。

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	图3 a 最优模型速度残差1999— 2007期及b 2013— 2017期结果Fig. 3 Residual velocities of the optimal model during 1999— 2007(a) and 2013— 2017(b).

1.3 断层闭锁与滑动亏损结果

根据最优模型得到了1999— 2007期(图4a)(赵静等, 2015)和2013— 2017期(图4b)2期鲜水河断裂闭锁程度的空间动态变化分布。图4a结果显示, 鲜水河断裂南东段的八美— 磨西附近在汶川地震前闭锁程度很高, 闭锁深度达到了断层模型的底部; 道孚— 八美附近地表至10km深度为强闭锁状态, 从10km至断层模型的底部闭锁程度快速降低, 转变为无滑动亏损积累状态; NW段侏倭— 道孚附近由于1893年至今地震活跃期中多次M6.7以上地震造成了大部分断层段破裂, 因此闭锁很弱, 基本处于蠕滑状态, 只有炉霍东南部一段断层地表至5km深度最大闭锁程度约0.73。图4b结果显示, 鲜水河断裂南东段的八美— 磨西附近在汶川地震后由强闭锁状态转变为无滑动亏损和能量积累状态; 道孚— 八美附近闭锁范围有所减少, 只有一小段断层闭锁依然较强, 还处于应力的逐渐积累状态; NW段侏倭— 道孚附近在震后闭锁程度变化较小, 基本还处于蠕滑状态, 只有炉霍东南部一段断层地表至10km深度闭锁稍有增强, 最大闭锁程度约0.93。对比赵静等(2015)中利用2009— 2013期GPS速度场反演所得鲜水河断裂闭锁程度结果可知, 汶川地震对鲜水河断裂尤其SE段的运动变形和应力应变能积累所产生的影响依然在持续。

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	图4 a 鲜水河断裂闭锁程度1999— 2007期及 b 2013— 2017期结果Fig. 4 Locking degree of the Xianshuihe Fault during 1999— 2007(a) and 2013— 2017(b).

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	图5 a 鲜水河断裂平行断层滑动亏损速率1999— 2007期及 b 2013— 2017期结果Fig. 5 Parallel fault slip deficit of the Xianshuihe Fault during 1999— 2007(a) and 2013— 2017(b).

图5为根据最优模型得到的鲜水河断裂平行断层滑动亏损速率, 2期结果显示沿整条断裂均为左旋走滑亏损(正值)。图5a显示鲜水河断裂南东段完全闭锁部分在汶川地震前滑动亏损速率为9.7~14.5mm/a, 其中道孚— 康定段滑动亏损速率基本保持约10mm/a, 在磨西附近滑动亏损速率达到最大; 鲜水河断裂NW段由于基本处于蠕滑状态, 因此基本没有滑动亏损积累。图5b显示鲜水河断裂SE段和NW段在汶川地震后基本都无滑动亏损和能量积累, 道孚— 八美之间闭锁较强的一段断层左旋运动有所减弱, 左旋走滑亏损速率最大值约6.1mm/a。

图6为根据最优模型得到的鲜水河断裂垂直断层滑动亏损速率, 2期结果显示沿整条断裂既有挤压亏损(负值)、也有拉张亏损(正值)。图6a显示汶川地震前只有鲜水河断裂最南端磨西附近为挤压, 最大挤压滑动亏损速率约5.1mm/a; 道孚— 康定段为拉张, 拉张滑动亏损速率为0.5~2.0mm/a; NW段基本处于蠕滑状态, 因此没有滑动亏损积累。图6b显示汶川地震后鲜水河断裂最南端磨西附近挤压亏损范围有所减少, 最大挤压滑动亏损速率降低为约4.0mm/a; 道孚— 八美之间闭锁较强的一段断层拉张有所增强, 拉张滑动亏损速率最大值约2.9mm/a。鲜水河断裂南端磨西附近已经接近安宁河断裂带, 在该位置开始逐步由拉张运动转变为挤压运动, 而汶川地震以后, 龙门山断裂带附近的巴颜喀拉块体E向运动明显增强, 因此造成磨西附近挤压运动有所减弱。

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	图6 a 鲜水河断裂垂直断层滑动亏损速率1999— 2007期及 b 2013— 2017期结果Fig. 6 Vertical fault slip deficit of the Xianshuihe Fault during 1999— 2007(a) and 2013— 2017(b).

2 鲜水河断裂带水准计算结果

2.1 水准场地与断层年均变化速率计算原理

本研究所用跨断层短水准场地沿鲜水河断裂带从NW至SE依次为侏倭、格篓、虚墟、沟普、龙灯坝、老乾宁、折多塘和安顺场地(图1), 水准数据时间跨度为1980— 2017年。

断层的年均变化速率计算公式为

$V_{t} = \frac{1}{n} \sum_{i = 1, n} (h_{i}^{t} - h_{i}^{t - 1}) (i = 1, 2 \dots, n) (1)$

式中, n为1a中所观测的期数, $h_{i}^{t}$ 为第ta中第i个观测值(江在森等, 2001; 李媛等, 2016)。

2.2 水准计算结果

根据式(1)计算了鲜水河断裂带上8个跨断层场地的年均垂直变化速率, 其中数据以2008年5月12日汶川地震、 2013年4月20日芦山地震和2014年11月22日康定地震的发生为分割点分别划分为2个时间段进行计算和展示。

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	图7 鲜水河断裂年均垂直变化速率(1980— 2017年)Fig. 7 Annual vertical change rate of the Xianshuihe Fault(1980— 2017).

图7显示鲜水河断裂带的年均垂直变化速率具有明显的分段特征, NW段侏倭、格篓、虚墟和沟普场地(以虚线三角点表示)年均垂直变化速率较大, 断层垂向运动处于较为活跃状态; 中南段龙灯坝、老乾宁、折多塘场地(以实线圆点表示)年均垂直变化速率较小, 多在0值附近波动, 断层垂向运动很弱, 处于闭锁状态; 南端安顺场地(以实线方框表示)年均速率变化幅度也相对较小。闻学泽(2000)利用1980— 1995年鲜水河断裂垂直形变数据研究表明松林口— 乾宁段是1893年M7地震破裂的主体, 由于至今该段落未发生M6.7以上地震, 因此目前断面仍处于闭锁状态; 方颖等(2015)利用1986— 2013年鲜水河断裂跨断层形变资料研究表明, 炉霍段、道孚段和乾宁西段闭锁弱, 而乾宁中东段闭锁强; Zhang等(2018)利用1976— 2014年鲜水河断裂跨断层形变资料研究表明, 龙灯坝、老乾宁附近处于强闭锁状态, 这些研究成果与本文计算的结果基本一致。整个鲜水河断裂带断层年均垂直变化速率受汶川地震的影响不大, 地震前后各场地并未发生明显改变, 这与GPS水平速度场结果受汶川地震影响较大有所不同, 可能有几个原因, 一是可能由于GPS测点多为远场观测, 而跨断层短水准观测为近场观测, 它们所反映的断层活动信息有所不同; 二是鲜水河断裂本身以走滑运动为主, 可能汶川地震对其垂向运动的影响不明显。芦山地震前, 格篓场地年均速率有所增大, 并在芦山地震后继续增大, 2014年开始年均速率恢复正常; 其他场地在芦山地震前后没有发生较明显变化。康定地震后, 折多塘场地年均速率变化并不明显, 2016年其年均速率有所增大, 主要是因为2016年5月C测点被压埋, 使之产生下沉, 造成C— B测段相对于4月变化了1.68mm, 后面还需继续关注其变化; 其他场地在康定地震前后也没有发生较明显变化。此外, 沟普场地在2014年4月由于附近施工对A测点周边造成了干扰影响, 使其年均垂直变化速率明显增大, 而非断层构造运动引起。

3 结论与讨论

(1)2014年11月22日鲜水河断裂带发生了康定M6.3地震, 为了研究康定地震对鲜水河断裂闭锁程度和跨断层短水准测量结果的影响, 对比了2011— 2013期和2013— 2017期2个时段GPS反演结果, 结果表明鲜水河断裂带闭锁程度并没有发生明显改变, 鲜水河断裂SE段的八美— 磨西附近在汶川地震后、康定地震前(即2011— 2013期结果)已经由强闭锁状态转变为无滑动亏损和能量积累状态; 道孚— 八美附近闭锁程度也已经明显减弱, 因此分析认为鲜水河断裂在1999— 2007年和2013— 2017年2个时段具有明显不同的闭锁程度与康定地震无关。将年均垂直变化速率以2014年11月22日康定地震的发生为分割点划分为2个时间段进行了对比, 结果表明各个场地在康定地震前后没有发生较明显变化。

(2)1999— 2007期负位错反演结果显示, 汶川地震前鲜水河断裂SE段闭锁程度很高, 中段闭锁程度逐渐减弱, 到NW段基本为蠕滑状态, 其中南段康定— 磨西附近强闭锁区域对应康定段和磨西段高库仑应力积累和增加区(Papadimitriou et al., 2004; 徐晶等, 2013); 中段八美附近强闭锁区域基本能够对应八美附近地震空区(Wen et al., 2008; 易桂喜等, 2015)、道孚— 乾宁段低b值区(易桂喜等, 2008)和八美段高库仑应力积累区(徐晶等, 2013), 与Zhang等(2018)给出的龙灯坝和老乾宁附近的强闭锁区域也基本一致; NW段距离下1次大地震还有较长的时间, 目前大部分还处于震后蠕滑阶段(闻学泽, 2000)。2013— 2017期负位错反演结果显示, 鲜水河断裂SE段受汶川震后影响较为明显, 基本无滑动亏损和能量积累, 只有道孚— 八美段之间有一小段闭锁较强; NW段依然大部分为蠕滑状态, 只有炉霍东南部一段断层地表至10km深度闭锁稍有增强。

(3)跨断层短水准结果显示, 鲜水河断裂NW段侏倭、格篓、虚墟和沟普场地年均垂直变化速率较大, 断层垂向活动较为活跃; 中南段龙灯坝、老乾宁、折多塘场地年均垂直变化速率较小, 多在0值附近波动, 断层垂向运动处于闭锁状态; 南端安顺场地年均速率变化幅度也相对较小。整个鲜水河断裂带汶川震后断层垂向活动变化不明显。

(4)1999— 2007期GPS速度场反演所得鲜水河断裂闭锁程度与跨断层短水准计算所得断层年均垂直变化速率具有较好的一致性, 都表明鲜水河断裂NW段断层较为活跃, 闭锁较弱; 鲜水河断裂SE段断层活动较弱, 闭锁较强。结合鲜水河断裂带三维变形特征和1893年至今的地震活动、库仑应力累积、 b值分布等结果, 分析认为, 相对于断裂NW段, 其SE段的地震危险性更高; 而汶川地震后巴颜喀拉地块向四川盆地的挤压运动速率加快, 从而降低了鲜水河断裂的远场左旋走滑速率(方颖等, 2010; 赵静等, 2015)和断层滑动亏损积累速率, 可能会减慢鲜水河断裂尤其南东段应力应变积累速率、缓解了其大震的发震紧迫性。

致谢湖北省地震局和王敏研究员为本研究提供GPS速度场资料; 苏琴高工就有关跨断层短水准资料给予的解释; 审稿专家提出的宝贵意见和建议, 在此一并表示感谢!

The authors have declared that no competing interests exist.

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[13]	玄松柏, 申重阳, 谈洪波. 2015. 芦山—康定地区布格重力异常及其归一化梯度图像的构造物理涵义[J]. 地球物理学报, 58(11): 4007—4017. XUAN Song-bai, SHEN Chong-yang, TAN Hong-bo. 2015. Tectonic implications of images of Bouguer gravity anomaly and its normalized full gradient in Lushan-Kangding area[J]. Chinese Journal of Geophysics, 58(11): 4007—4017(in Chinese). [本文引用:1]
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[16]	赵静, 江在森, 牛安福, 等. 2015. 川滇菱形块体东边界断层闭锁程度与滑动亏损动态特征研究[J]. 地球物理学报, 58(3): 872—885. doi: DOI: 106038/cjg20150316. ZHAO Jing, JIANG Zai-sen, NIU An-fu, et al. 2015. Study on dynamic characteristics of fault locking and fault slip deficit in the eastern boundary of the Sichuan-Yunnan rhombic block[J]. Chinese Journal of Geophysics, 58(3): 872—885(in Chinese). [本文引用:7]
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2010

0.0

... 小江断裂带和龙门山断裂带相接, 构成了川滇菱形块体、巴颜喀拉地块、华南地块的交叉口(方颖等, 2010) ...

... 小江断裂带、龙门山断裂带在青藏高原东缘构成了交叉口(方颖等, 2010 ...

... 而汶川地震后巴颜喀拉地块向四川盆地的挤压运动速率加快, 从而降低了鲜水河断裂的远场左旋走滑速率(方颖等, 2010 ...

2015

0.0

方颖, 张晶, 江在森, 等. 2015. 用跨断层形变资料分析鲜水河断裂西北段的运动特征[J]. 地球物理学报, 58(5): 1645—1653.

FANG

Ying

, ZHANG

Jing

, JIANG

Zai-sen

, et al. 2015. Movement characteristics of the northwest segment of the Xianshuihe fault zone derived from cross-fault deformation data[J]. Chinese Journal of Geophysics, 58(5): 1645—1653(in Chinese).

本文利用主成分分析、震间位错反演和小波技术分析了鲜水河断裂西北段的跨断层形变资料(1986—2013).结果表明:以左旋走滑为主的断层长期运动为跨断层资料的主要信息,且符合负指数函数的运动规律,随着断层深度的增加,滑动量逐渐减弱.从炉霍段、道孚段到乾宁段,断层闭锁程度逐渐增强.2001年昆仑山M8.1地震发生后,鲜水河断裂西北段地壳浅层(地表以下30km)的左旋走滑明显减弱,到2013年的累积减弱量为3~13mm.5·12汶川M8.0地震发生前,断层滑动出现周期4~5年的增强信号.4·20芦山M7.0地震发生前,断层滑动首先出现低频信号(4~5年周期)增强,随着地震发生临近,强信号频率逐渐升高,直到出现周期为1年的强信号.

... 方颖等(2015)利用1986#cod#x02014 ...

2017

0.0

何梅兴, 方慧, 王绪本, 等. 2017. 鲜水河断裂带南段深部电性结构特征研究[J]. 地球物理学报, 60(6): 2414—2424. doi: DOI: 106038/cjg20170630.

Mei-xing

, FANG

Hui

, WANG

Xu-ben

, et al. 2017. Deep conductivity characteristics of the southern Xianshuihe fault zone[J]. Chinese Journal of Geophysics, 60(6): 2414—2424(in Chinese).

摘　要：通过对新都桥—小金剖面的大地电磁测深及重磁实测资料研究，结合区域地质资料，对鲜水河断裂带南段及邻区深部构造、壳内高导层、电性结构与历史地震的关系进行了研究.结果表明：（1）鲜水河断裂带深浅表现出不同特征，浅部是以地壳脆性-剪切带为主的断裂系统，深部是以走滑型-壳幔韧性剪切带为主的断裂系统，断裂呈花状形态，深部到达上地幔；（2）在丹巴构造带及鲜水河断裂带的中下地壳，广泛发育壳内高导层，其分布具有不均匀性，且与断裂带构造活动有关；（3）在鲜水河断裂带的走滑剪切作用下，上地壳物质发生原地重熔产生花岗岩浆是折多山花岗岩形成的主要机制；（4）鲜水河断裂带地震发生机理与塑性软弱层密切相关，受塑性软弱层拖拽作用，应力区集中在高阻体脆性介质内部靠近断层一侧，使得岩石破碎而发生地震.

... 鲜水河断裂带SE段深部电性结构研究结果表明, 中上地壳断裂带构造表现出花状构造, 既有倾角陡立并且切穿地壳的深大断裂, 也有倾角稍缓会聚于深大断裂的小断裂(何梅兴等, 2017), 因此雅拉河、折多塘、色拉哈-磨西等断裂可能在深部会聚于1条主干断裂 ...

2001

0.0

... 式中, n为1a中所观测的期数, hit为第ta中第i个观测值(江在森等, 2001 ...

2016

0.0

李腊月, 季灵运, 李玉江, 等. 2016. 基于跨断层测量的鲜水河断裂带现今活动特征及其与强震关系研究[J]. 地震学报, 38(5): 739—750.

La-yue

, JI

Ling-yun

, LI

Yu-jiang

, et al. 2016. Current activity characteristics of Xianshuihe fault zone and its relationship with strong earthquakes based on fault-crossing measurements[J]. Acta Seismologica Sinica, 38(5): 739—750(in Chinese).

... 苏琴等(2012)、李腊月等(2016)利用跨断层短水准和基线结果对鲜水河断裂带断层活动特征进行了分析 ...

2016

0.0

李媛, 刘峡, 刘希康, 等. 2016. 2016年门源 M_S6. 4地震前祁连山周边断层活动分析[J]. 大地测量与地球动力学, 36(4): 288—293.

Yuan

, LIU

Xia

, LIU

Xi-kang

, et al. 2016. Activity analysis of faults around Qilianshan before the 2016 Menyuan M_S6. 4 earthquake[J]. Journal of Geodesy and Geodynamics, 36(4): 288—293(in Chinese).

The across-fault data of the Qilianshan-Haiyuan fault zone presents obvious precursory anomalies before the Menyuan Ms6.4 earthquake. We study deformation phenomena and activities of faults around Qilianshan before the earthquake. Based on the latest across-fault data in the northeastern margin of Tibet plateau, and by using a variety of methods, including temporal curve analysis, the fault rate of the synthetic analysis method, and the vertical deformation rate, this article extracts anomaly characteristics and reveals fault activity from different angles and scopes. The results are as follows: (1) Within 150 km epicentral distance, multiple sites present typical short-term anomalies, which are mainly accelerated and extensional changes; within 150-300 km, the anomaly type gives priority to trend variation. (2) The spatial distribution of anomaly stations shows that anomaly stations, concentrated in the middle of Qilianshan fault, have the tendency to migrate to the east and concentrate in the middle-eastern region. At the same time, the anomaly in Haiyuan has increased. These phenomena are extremely similar to those before 2003 Minle Ms6.1 earthquake. (3) From 2014, the synthetic rate of Qilianshan fault deviates from the value of the normal far away, which means strain is easy to accumulate here. Further, according to results of vertical deformation trend accumulation rate, the earthquake epicenter is located in the high value area of deformation accumulation. So the occurrence of the earthquake had a certain degree of inevitability.

基于青藏高原东北缘地区最新的跨断层资料，利用时序曲线分析、断层速率合成分析和垂直形变累积率分析等多种方法进行计算，从不同角度和范围提取2016年门源Ms6.4地震震前异常特征，揭示断层活动。结果显示：1）震中距150 km以内多个场地出现了典型的以加速张性变化为主的短期异常，150~300 km内的异常以趋势变化为主；2）祁连山-海原断裂带上异常场地的空间分布表现出由祁连山断裂带中部集中向东迁移至中东部集中的特征，海原断裂上异常有所增多，此类现象与2003年民乐6.1级地震前的现象极其相似；3）祁连山断裂自2014年以来合成速率偏离正常动态值较远，容易积累应变。垂直形变趋势累积率的计算结果显示，地震震中位于形变积累的高值区。

... 李媛等, 2016) ...

2006

0.0

冉洪流, 何宏林. 2006. 鲜水河断裂带北西段不同破裂源强震震级( M≥6. 7)及复发间隔研[J]. 地球物理学报, 49(1): 153—161.

RAN

Hong-liu

, HE

Hong-lin

. 2006. Research on the magnitude and recurrence interval of characterized earthquakes with magnitude≥6. 7 along the northwestern portion of the Xianshuihe fault zone in western Sichuan, China[J]. Chinese Journal of Geophysics, 49(1): 153—161(in Chinese).

The Xianshuihe fault in Sichuan Province, southwestern China is one of the major left_lateral strike_slip faults which emanate from Tibet and seem to play a key role in accommodation of Indias penetration into Eurasia. In the northwestern portion of the Xianshuihe fault zone, sixteen earthquakes of M≥65 occurred since 1700 The northwestern portion of the Xianshuihe fault zone can be divided into four segments based on field investigation of recent earthquake ruptures, studies on timespace distribution and recurrence behaviors of historical ruptures, geometry and structure of fault zones, geophysical background, and recent seismicity. Each segment of the fault is a unit that has produced historical ruptures and able to produce future ruptures independently. To evaluate the magnitude distribution and recurrence interval of the characterized earthquakes along the northwestern portion of the Xianshuihe fault zone, we develop a framework by taking into account new geologic, seismologic and geodetic information, extending the previous analysis through a keener appreciation of the “stress shadow" caste by historical events and the influence, and further developing a momentbalanced model. The result shows that all the recurrence intervals of singlesegment ruptures are about 100 to 150 years, which are much shorter than the recurrence intervals of cascade ruptures and the entire fault rupture.

Institute of Geology, China Earthquake Administration, Beijing 100029, China

鲜水河断裂带是四川西部一条晚第四纪强烈左旋走滑活动的构造带，历史上发生多次强震. 它与西北侧的甘孜—玉树断裂带一起，构成青藏高原东部的侧向滑移构造系统中的川滇活动地块的北边界——羌塘地块的东北边界. 鲜水河断裂带北西段可以分成4个段落，每一段落均可作为一个独立的基本破裂单元而发生地震破裂，亦有可能发生不同尺度的多段联合瞧裂. 对鲜水河断裂带北西段不同尺度破裂的震级及复发间隔进行研究. 根据该地区的地质、地球物理、测量及地震等方面的资料，结合我国强震复发的特点，分析了拉分盆地内部的滑动速率分布，以确定各段落的等效长度和倾向宽度，从而建立适合我国大陆走滑断裂的面波震级与断裂发震面积的关系式；进而运用地震矩方法，考虑断层之间的相互作用，结合专家意见建立了该段的矩平衡断裂破裂模型；最后，给出了鲜水河断裂带北西段各破裂源特征化地震的复发间隔、震级大小和不确定性，以及他与中小地震的联合震级分布. 结果表明，鲜水河断裂带北西段较易发生单段破裂，复发间隔在100～150年左右.

... 冉洪流等(2006)对鲜水河断裂带NW段、周荣军等(2001)对鲜水河断裂带乾宁#cod#x02014 ...

... 冉洪流等(2006)认为炉霍段的断层倾角为75#cod#x000b0 ...

2012

0.0

苏琴, 杨永林, 向和平. 2012. 汶川8. 0级地震前后鲜水河断裂带断层活动特征分析[J]. 四川地震, (1): 24—29.

Qin

, YANG

Yong-lin

, XIANG

He-ping

. 2012. Seismicity character analysis on the Xianshuihe faults before and after the 2008 Wenchuan M8. 0 earthquake[J]. Earthquake Research in Sichuan, (1): 24—29(in Chinese).

本文利用鲜水河主断裂带上的跨断层短水准、短基线以及水平蠕变资料，计算了各测点处断层的活动参数，分析了汶川8．0级地震前后断层的活动特征。研究结果认为：远离汶川8．0级地震震源区的鲜水河断裂带在震前3年出现了明显的长期趋势异常，但短期异常不明显，无明显的同震形变；从震后3年对鲜水河带跟踪监测的结果看，鲜水河断裂带受其影响中南段拉张活动有所增强，垂直向仍保持震前的活动形态。

... 苏琴等(2012)、李腊月等(2016)利用跨断层短水准和基线结果对鲜水河断裂带断层活动特征进行了分析 ...

2013

0.0

王丽凤, 刘杰, 赵金贵, 等. 2013. 2011年日本9. 0级地震的同震位错以及震后应力松弛过程对中国大陆的影响[J]. 地震, 33(4): 238—247.

WANG

Li-feng

, LIU

Jie

, ZHAO

Jin-gui

, et al. 2013. Coseismic slip and post-seismic relaxation of the 2011 M9. 0 Tohoku-Oki earthquake and its influence on China mainland [J]. Earthquake, 33(4): 238—247(in Chinese).

... 但黏弹性松弛衰减速率较慢, 震后影响时间长(王丽凤等, 2013) ...

2000

0.0

闻学泽. 2000. 四川西部鲜水河—安宁河—则木河断裂带的地震破裂分段特征[J]. 地震地质, 22(3): 239—249. doi: DOI: 103969/j. issn. 0253-4967. 2000. 03. 005.

WEN

Xue-ze

. 2000. Character of rupture segmentation of the Xianshuihe-Anninghe-Zemuhe fault zone, Western Sichuan[J]. Seismology and Geology, 22(3): 239—249(in Chinese).

Based on several types of data, segmentation and its cause, earthquake ruptures along the Xianshuihe-Anninghe-Zemuhe fault zone in western Sichuan are analyzed from various aspects. The fault zone is divided into 12 rupture-segments for characteristic earthquakes. Along this fault zone, the persistent and non-persistent boundaries of ruptures have almost the same number ratio of 2%. The persistent and important boundaries can be identified by criteria such as geometry, structure and active behavior of faults. They terminate the propagation of earthquake ruptures by partly volume-changing there. The non-persistent boundaries can be identified by criteria such as extension and recurrence behavior of earthquake ruptures, spatial difference of current active behavior of faults, composition of both relatively small-scale geometric barriers and release barriers. Locations of the non-persistent boundaries may vary with time. Relatively small overlap occurs between adjacent ruptures if the time interval between them is shorter, and relatively large overlap appears between adjacent ruptures if the time interval between them is longer.

Seismological Bureau of Sichuan Province, Chengdu 610041

依据多种资料分层次剖析了川西鲜水河-安宁河-则木河断裂带的地震破裂分段性及其原因,并将该断裂带划分为12个特征地震破裂段。断裂带上持久性和非持久性的破裂边界各占约2%;持久性及重要的破裂边界可依据断裂几何结构及活动习性标志进行判定,它们均以局部体积变化的方式来终止破裂的扩展;非持久性的破裂边界则可依据地震破裂与复发行为、断裂现今活动习性空间差异、松驰障碍体与较小尺度几何障碍的复合体等进行判定,其位置可随时间变化。地震破裂时间间隔短的,相邻破裂的重叠量较小;时间间隔长的,相邻破裂的重叠量则较大。

... 鲜水河断裂带为当今地学研究的热点断裂, 闻学泽(2000)、 Papadimitriou等(2004)和Wen等(2008)对鲜水河断裂带的地震破裂分段特征进行过细致的研究 ...

... 鲜水河断裂带SE段主要由4条分支断裂组成, 其中雅拉河与折多塘2条断裂均为较短的分支, 可分别看做独立的破裂段, 剩下的为主干断裂色拉哈-磨西断裂(闻学泽, 2000) ...

... 闻学泽(2000)利用1980#cod#x02014 ...

... NW段距离下1次大地震还有较长的时间, 目前大部分还处于震后蠕滑阶段(闻学泽, 2000) ...

2015

0.0

熊维, 谭凯, 乔学军, 等. 2015. 汶川震后龙门山周边活动地块构造变形及断裂活动[J]. 大地测量与地球动力学, 35(5): 758—763.

XIONG

Wei

, TAN

Kai

, QIAO

Xue-jun

, et al. 2015. Tectonic deformation and fault activity of active blocks in Longmenshan and surrounding area after Wenchuan earthquake[J]. Journal of Geodesy and Geodynamics, 35(5): 758—763(in Chinese).

Based on GPS velocity field data from 1999 to 2013, we calculate the train rate field and the Euler rotation vector of main blocks in Longmenshan and the surrounding area. Using these results as constraints, we calculate the slip rate and locking depth of the main active faults with the Rngchn program based on the Okada model, and then discuss regional tectonic deformation and strain distribution in the research area. Finally, we analyze the effect of the Wenchuan earthquake on the above process. The research shows that: most active blocks, such as east Bayan Har, northwest Sichuan and middle Yunnan, are moving to the southeast with a clockwise rotation at the same time. Due to the crustal strain absorption and adjustment of thrust belts such as the Longmenshan fault, the regional crustal deformation decreases gradually from the west to the east. The Wenchuan earthquake not only accelerated the motion of Bayan Har and northwest Sichuan block, but also enhanced the strike-slip and thrust movement of the Anninghe-Zemuhe-Xiaojiang fault and the Lijiang-Xiaojinhe fault.

利用1999~2013陆态网络观测资料，计算汶川地震前后龙门山地区周边活动地块应变率场分布及欧拉旋转矢量，基于Okada矩形位错模型，反演块体边界主要断层活动性状，分析研究区域现今构造变形和应变分配，并讨论汶川地震对上述过程的影响。[JP2]研究表明，巴颜喀拉东部、川西北、滇中等活动地块向南东向运移的同时自身作顺时针旋转|由于龙门山断裂、丽江-小金河断裂等逆冲带对地壳应变的吸收与调整，研究区域地壳变形由西向东逐渐减弱，区域地壳变形以连续渐变为主要特征|汶川地震使巴颜喀拉块体、川西北块体的南东向运移加速，并增强了安宁河-则木河-小江断裂带左旋走滑运动和丽江-小金河断裂的逆冲运动。

... 而川滇地块和巴颜喀拉地块由于内部变形明显(熊维等, 2015), 认为其存在整体旋转运动、内部永久应变和由于断层闭锁而产生的弹性应变 ...

2013

0.0

徐晶, 邵志刚, 马宏生, 等. 2013. 鲜水河断裂带库仑应力演化与强震间关系[J]. 地球物理学报, 56(4): 1146—1158.

Jing

, SHAO

Zhi-gang

, MA

Hong-sheng

, et al. 2013. Evolution of Coulomb stress and stress interaction among strong earthquakes along the Xianshuihe fault zone[J]. Chinese Journal of Geophysics, 56(4): 1146—1158(in Chinese).

... 徐晶等(2013)对1893年以来鲜水河断裂带库仑应力演化与区域强震的关系进行了研究 ...

... 徐晶等, 2013) ...

... 徐晶等, 2013), 且早期的GPS和InASR数据研究结果表明道孚#cod#x02014 ...

... 另外, 本文还参考了其他一些文献中关于鲜水河断裂带NW段断层倾角的研究结果, 其中Papadimitriou等(2004)和徐晶等(2013)将炉霍、恰叫、道孚、八美段的断层倾角均设置为90#cod#x000b0 ...

... 另外, Papadimitriou等(2004)和徐晶等(2013)将雅拉河与折多塘段的断层倾角设置为75#cod#x000b0 ...

... 徐晶等, 2013) ...

... 乾宁段低b值区(易桂喜等, 2008)和八美段高库仑应力积累区(徐晶等, 2013), 与Zhang等(2018)给出的龙灯坝和老乾宁附近的强闭锁区域也基本一致 ...

2015

0.0

... 玄松柏等, 2015), 这3条断裂带之间的运动与变形存在着相互影响, 因此本研究在建立块体和断层系统模型时同时考虑了上述3条断裂带, 将整个研究区域以它们为边界, 划分为川滇地块、巴颜喀拉地块和华南地块(图1) ...

2015

0.0

易桂喜, 龙锋, 闻学泽, 等. 2015. 2014年11月22日康定 M6. 3地震序列发震构造分析[J]. 地球物理学报, 58(4): 1205—1219. doi: DOI: 106038/cjg20150410.

Gui-xi

, LONG

Feng

, WEN

Xue-ze

, et al. 2015. Seismogenic structure of the M6. 3 Kangding earthquake sequence on 22 Nov. 2014, Southwestern China[J]. Chinese Journal of Geophysics, 58(4): 1205—1219(in Chinese).

On 22 Nov. 2014, an M 6.3 earthquake hit Kangding County in Sichuan Province, southwestern China. 3 days later, another M 5.8 earthquake occurred in the same region, about 10 km southeastwards from the epicenter of the M 6.3 mainshock. Both earthquakes were on the NW-striking Xianshuihe fault zone where no M ≥6.0 earthquakes were reported after the 1982 M 6.0 Ga nz i event. From the relocated aftershock distribution and focal mechanism solutions, we aim to analyze the seismogenic structure of the 2014 M 6.3 Kangding earthquake sequence. Along with the analysis on the characteristics of the strong earthquake ruptures and the spatial distribution of the relocated small earthquakes, we will further discuss the future strong-earthquake risk between Daofu and Kangding on the central segment of the Xianshuihe fault zone.Based on the digital waveform data from China National Seismic Network and Sichuan Regional Network, the Kangding earthquake sequence was relocated by a multi-step locating method developed by Long et al. The focal mechanism solutions and the centriod depths of the M 6.3 and M 5.8 earthquakes were inverted simultaneously by the gCAP (generalized Cut and Paste) moment tensor inversion method. The spatial-temporal distribution of the M ≥6.5 strong earthquake ruptures since 1725 and the focal depth distribution of relocated small earthquakes from Jan. 2001 to Oct. 2014 along the central-southern segment of the Xianshuihe fault zone were used to identify the potential seismogenic region of the next strong earthquakes on the segment between Daofu and Kangding.The epicentral relocation of the M 6.3 mainshock is at 101.69°E、30.27°N, and its initial rupture depth is about 10 km, while the centroid depth is 9 km; the relocated M 5.8 earthquake is at 101.73°E、30.18°N with the initial rupture depth at about 11 km and the centroid depth of 9 km. The moment tensor solutions from gCAP method show that the two events are dominated by the double-couple component. The parameters of the best double-couple solutions are as follows, strike 143°, dip 82°, rake -9° for nodal plane Ⅰ, and strike 234°, dip 81°, rake -172° for nodal plane Ⅱ for the M 6.3 earthquake. For the M 5.8 earthquake, the parameters are listed as, strike 151°, dip 83°, rake -6° for the nodal plane Ⅰ, and strike 242°, dip 84°, rake -173° for the nodal plane Ⅱ. Most aftershocks during the first 3 days were distributed on the NW side of the M 6.3 mainshock, and majority of the aftershocks after M 5.8 earthquake were concentrated around the epicenter of the M 5.8 event. The average focal depth of the 459 relocated earthquakes of the sequence is about 9 km. Focal depth distribution reveals that the sequence mainly concentrated in the depth range of 6~11 km and most of the aftershocks are shallower than the M 6.3 and M 5.8 earthquakes. The seismic source scale is estimated to be about 30 km in length and 4 km in width with 6 km in depth according to the aftershock distribution. On the space-time diagram of the historical M ≥6.5 strong earthquake ruptures, we observe a gap on the Selaha fault of the central Xianshuihe fault zone, where no M ≥6.5 earthquakes occurred since the 1748 M 6 1 / 2 event. Aseismic gap below the depth 7 km between Kangding and Tagong and a low-seismicity region below the depth 2 km between Tagong and Songlinkou were identified on the vertical cross-section of the relocated small earthquakes since 2001 along the central-southern segment of the Xianshuihe fault zone.The nodel planeⅠof the focal mechanism solution was interpreted as the coseismic rupture plane for the M 6.3 and M 5.8 earthquakes based on the aftershock distribution and the fault strike. Both earthquakes are of left-lateral strike-slip faulting with some normal component. The relocated M 6.3 earthquake and its aftershocks during the first three days are on the NW-striking Selaha fault with a near-vertical dip angle of 82°, while the M 5.8 earthquake and its adjacent aftershocks are on the northern portion of the NW-striking Zheduotang fault with a dip angle of 83°, implying that the M 5.8 earthquake on the Zheduotang fault may be induced by the M 6.3 earthquake in the adjacent Selaha fault. The scarce aftershock region around the M 6.3 mainshock may belong to a relatively large asperity where the accumulated energy was totally released as the M 6.3 mainshock occurred. The 2014 M 6.3 Kangding earthquake sequence occurred within the Selaha strong-earthquake rupture gap between Qianning and Kangding. Due to the duration of quiescence longer than the estimated average recurrence interval for the M 7 earthquakes, we propose that the ruptures of the M 6.3 and M 5.8 earthquakes are too limited to fill up the gap, posing future M 7 earthquake risk on the Selaha and its adjacent Qianning segments along the central segment of the Xianshuihe fault zone. Since most area of the previous seismic gap below the depth 7 km between Kangding and Tagong along the central-southern Xianshuihe fault zone was filled by the 2014 M 6.3 Kangding earthquake sequence, and the most likely place of future strong earthquake occurrence will be below the segment between Tagong and Songlinkou where low seismicity is observed.

1. Earthquake Administration of Sichuan Province, Chengdu 610041, China; 2. Sichuan Seistech Corporation Ltd., Chengdu 610041, China; 3. State Key Laboratory of Earthquake Dynamics, Institute of Geology, China Earthquake Administration, Beijing 100029, China; 4. Institute of Geology, China Earthquake Administration, Beijing 100029, China

2014年11月22日在NW向鲜水河断裂带中南段四川康定县发生 M 6.3级地震,11月25日在该地震震中东南约10 km处再次发生 M 5.8级地震. 基于中国国家数字地震台网和四川区域数字地震台网资料,采用多阶段定位方法对本次康定 M 6.3级地震序列进行了重新定位; 利用gCAP(generalized Cut And Paste) 矩张量反演方法获得了 M 6.3和 M 5.8级地震的震源机制解与矩心深度,分析了本次地震序列的发震构造,并结合历史强震破裂时空分布和2001年以来小震重新定位结果,对鲜水河断裂带中段强震危险性进行了初步探讨. 获得的主要结果如下:(1) M 6.3级主震震中位于101.69°E、30.27°N,震源初始破裂深度约10 km,矩心深度9 km; M 5.8级地震震中位于101.73°E、30.18°N,初始破裂深度约11 km,矩心深度9 km. gCAP矩张量反演结果揭示这两次地震双力偶分量占主导, M 6.3级地震的最佳双力偶解节面Ⅰ走向143°/倾角82°/滑动角-9°,节面Ⅱ走向234°/倾角81°/滑动角-172°. M 5.8级地震最佳双力偶解节面Ⅰ走向151°/倾角83°/滑动角-6°,节面Ⅱ走向242°/倾角84°/滑动角-173°. 依据余震分布长轴展布与断裂走向,判定节面Ⅰ为发震断层面, M 6.3和 M 5.8级地震均为带有微小正断分量的左旋走滑型地震. (2) 序列中重新定位的459个地震平均震源深度约9 km,地震主要集中分布在6~11 km深度区间,余震基本发生在 M 6.3和 M 5.8级地震震源上部. 依据余震密集区展布范围,推测本次康定地震的震源体尺度长约30 km、宽约4 km、深度范围约6 km. M 6.3级主震震源附近的余震稀疏区可能是一个较大的凹凸体(asperity),在主震中能量得以充分释放. (3) 最初3天的余震主要分布在 M 6.3级地震NW侧;而 M 5.8级地震之后的余震主要集中在其震中附近. M 6.3级地震以及最初3天的绝大部分余震发生在倾角约82°近直立的NW走向色拉哈断裂上; M 5.8级地震与其后的多数余震发生在倾角约83°近直立的NW走向折多塘断裂北端走向向北偏转部位, M 5.8级地震可能是 M 6.3级地震触发相邻的折多塘断裂活动所致. (4) 康定 M 6.3与 M 5.8级地震发生在鲜水河断裂带乾宁与康定之间的色拉哈强震破裂空段,本次地震破裂尺度较小,尚不足以填补该强震空段. 色拉哈段以及相邻的乾宁段7级地震平静时间均已超过其平均复发周期估值,未来几年存在发生7级地震的危险. 康定 M 6.3级地震序列基本填补了震前存在于塔公与康定之间的深部小震空区,未来强震发生在塔公至松林口段深部小震稀疏区内的可能性很大.

... Zhang等(2018)对鲜水河断裂带NW段、易桂喜等(2015)对鲜水河断裂带康定段的断层面参数进行了研究 ...

... 3地震后, 易桂喜等(2015)利用gCAP矩张量反演和地震序列重新定位的方法分析认为, 色拉哈断裂倾角约为82#cod#x000b0 ...

... 易桂喜等, 2015)、道孚#cod#x02014 ...

2008

0.0

易桂喜, 闻学泽, 苏有锦. 2008. 川滇活动地块东边界强震危险性研究[J]. 地球物理学报, 51(6): 1719—1725.

Gui-xi

, WEN

Xue-ze

, SU

You-jin

. 2008. Study on the potential strong-earthquake risk for the eastern boundary of the Sichuan-Yunnan active faulted-block, China[J]. Chinese Journal of Geophysics, 51(6): 1719—1725(in Chinese).

Taken the eastern boundary of the Sichuan-Yunnan active faulted-block in southwestern China as an example，spatial stress distribution and potential strong-earthquake risk have been studied based on detailed b value calculation from seismic data of the last 31 years. The main results show: (1) The spatial distribution of b values displays significant heterogeneity for various faults and fault-segments of the eastern boundary of the Sichuan-Yunnan active faulted-block, which reflects the spatial difference of cumulative stress level along the boundary fault zones. (2) There are several asperities, one located at Songming on Xiaojiang main fault, one between Qiaojia and Dongchuan, and one at northwestern Songming near the main fault, two near Mianning on Anninghe fault and near Xichang on Zemuhe fault, and a large-scale one from Daofu to Qianning on central-southern portion of the Xianshuihe fault. The asperities may be the potential seismogenic sources of large or strong earthquakes along the eastern-boundary in the near future.

以川滇活动地块东边界为例，利用最近31年的地震资料，根据精细 b 值计算结果，研究该边界断裂带的应力空间分布及其强震危险性. 研究结果显示：（1）沿川滇活动地块东边界， b 值空间分布显示在不同断裂以及同一断裂不同断裂段存在较大差异，从而反映出应力积累水平的空间差异.（2）小江断裂带主干断裂上的嵩明凹凸体及存在于主干断裂附近巧家与东川间以及嵩明北西的2个凹凸体、存在于安宁河断裂冕宁附近和则木河断裂西昌附近的凹凸体以及位于鲜水河断裂中南段道孚—乾宁间大尺度的凹凸体将是川滇活动地块东边界未来大震或强震的震源区.

... 乾宁段低b值区(易桂喜等, 2008)和八美段高库仑应力积累区(徐晶等, 2013), 与Zhang等(2018)给出的龙灯坝和老乾宁附近的强闭锁区域也基本一致 ...

2015

0.0

赵静, 江在森, 牛安福, 等. 2015. 川滇菱形块体东边界断层闭锁程度与滑动亏损动态特征研究[J]. 地球物理学报, 58(3): 872—885. doi: DOI: 106038/cjg20150316.

ZHAO

Jing

, JIANG

Zai-sen

, NIU

An-fu

, et al. 2015. Study on dynamic characteristics of fault locking and fault slip deficit in the eastern boundary of the Sichuan-Yunnan rhombic block[J]. Chinese Journal of Geophysics, 58(3): 872—885(in Chinese).

... 赵静等, 2014, 2015)必须要区分断层的上下盘, 且同1条断层的上下盘不能随深度发生改变, 因此将NW段断层断面参数设定为NE∠85#cod#x000b0 ...

... 赵静等, 2014, 2015) ...

... 图3a结果表明, 除了安宁河断裂东边几个测点、川滇地块西边界几个测点、巴颜喀拉块体西端几个测点速度残差值稍大以外, 其他位置测点的速度残差值较小, 大部分处在误差范围之内(赵静等, 2015) ...

... 图3b结果表明, 除了安宁河断裂东边几个测点、川滇地块西边界几个测点、龙门山断裂中北段附近部分测点速度残差值较大以外, 其他位置测点的速度残差值较小, 这与赵静等(2015)中2009#cod#x02014 ...

... 2007期(图4a)(赵静等, 2015)和2013#cod#x02014 ...

... 对比赵静等(2015)中利用2009#cod#x02014 ...

... 赵静等, 2015)和断层滑动亏损积累速率, 可能会减慢鲜水河断裂尤其南东段应力应变积累速率、缓解了其大震的发震紧迫性 ...

2013

0.0

赵静, 江在森, 武艳强, 等. 2013. Defnode负位错模型反演结果的可靠性和稳定性分析[J]. 大地测量与地球动力学, 33(1): 21—24.

ZHAO

Jing

, JIANG

Zai-sen

, WU

Yan-qiang

, et al. 2013. Analysis of reliability and stability of inversion result with negative dislocation model of Defnode[J]. Journal of Geodesy and Geodynamics, 33(1): 21—24(in Chinese).

Using analog data and measured GPS velocity field, we analyzed the influence of different fault dip angles, different weight f and data spatial distribution on the negative dislocation inversion program of Defnode. The inversion results of analog data show that the inversion results both have a high degree of reliability under conditions of low dip angle and high dip angle.Measured GPS velocity field inversion results of the Longmenshan fault zone show that they have good stability and the weight f has little influence on the inversion results, and the distribution of GPS observation stations (especially the quantity and location of stations near the fault zone) has certain influence on the inversion results, but it can not change the fact that the southern segment is a little less locked than the middlenorthern segment.

利用模拟数据和实测GPS速度场，分析了断层倾角、权值 f 、数据空间分布等对Defnode负位错反演程序的影响。模拟数据反演结果表明，在低倾角与高倾角条件下反演结果均具有高度可靠性。龙门山断裂带实测GPS速度场反演结果表明，反演结果具有很好的稳定性，权值 f 对反演结果的影响微乎其微；GPS观测站点的分布（特别是断裂带附近站点的数量和位置）对反演结果有一定影响，但是没有改变龙门山断裂带南段闭锁程度相对中北段较弱的整体分布情况。

... 权值f对反演结果影响微弱, 反演结果具有很好的稳定性(赵静等, 2013) ...

2014

0.0

赵静, 刘杰, 牛安福, 等. 2014. 大凉山次级块体周边断层的闭锁特征[J]. 地震地质, 36(4): 1135—1144. doi: DOI: 103969/j. issn. 0253-4967. 2014. 04. 016.

ZHAO

Jing

, LIU

Jie

, NIU

An-fu

, et al. 2014. Study on fault locking characteristic around the Daliangshan sub-block[J]. Seismology and Geology, 36(4): 1135—1144(in Chinese).

GPS campaign observations can monitor dynamic characteristic of crustal deformation near the fault zone effectively. Dynamic characteristic of crustal deformation is the manifestation of the dynamic action of the faults in deep and shallow structures. The locking and movement state of faults in deep and shallow structures can be an objective characterization of strain accumulation in seismogenic fault. So we can use dynamic GPS observations to invert fault locking and fault slip deficit rate by some models, and then judge the mid- to long-term seismic potential of the faults. Research about the faults around the Daliangshan sub-block is relatively poor, and the moderate-strong earthquakes increased significantly around the sub-block over the past decade, which makes fault locking and seismic potential around the sub-block be the problem to be urgently studied. Therefore, by using the GPS horizontal velocity field of 1999-2007, 2009-2013 and the negative dislocation model of DEFNODE, we inverted for spatial fault locking and fault slip deficit rate in the Daliangshan sub-block which contains three major fault zones, named Daliangshan, Mabian-Yanjin and Huize-Yiliang, before and after the Wenchuan earthquake. We analyzed the seismic potential characteristic of the three faults combining with the seismic gap and the spatial distribution of b value. The results show that the locking state of the three faults was basically same before and after the Wenchuan earthquake, which indicates that the earthquake probably has a very weak influence on the faults. The inversion results of two periods show that the southern segment of Daliangshan, Mabian-Yanjin and Huize-Yiliang Faults are basically completely locked except the southwestern segment of Huize-Yiliang Fault. The slip deficit rates of the three faults are not huge before and after the earthquake. Daliangshan Fault is mainly of a sinistral strike-slip deficit, Mabian-Yanjin Fault has a little amount of sinistral strike-slip and compressional deficit which was slightly enhanced after the earthquake, and Huize-Yiliang Fault is characteristic of compressional deficit with a small amount of dextral strike-slip deficit, which reduced to about zero after the earthquake. Combining with some other results, we conclude that current seismic potential for strong or major earthquakes exists on the three faults.

利用1999—2007期和2009—2013期中国大陆GPS速度场数据, 采用DEFNODE负位错反演程序估算了大凉山次级块体周边断层——大凉山断裂、马边-盐津断裂、会泽-彝良断裂在汶川地震前后的断层闭锁程度和滑动亏损空间分布动态变化特征, 并结合地震空区和 b 值空间分布等结果分析了这几条断裂带的强震危险性.结果表明, 汶川地震对这3条断裂带的影响可能较弱, 它们在地震前后闭锁程度基本一致, 两期结果均显示大凉山断裂南段、马边-盐津断裂、会泽-彝良断裂(西南端除外)基本为完全闭锁;汶川地震前后3条断裂带的滑动亏损速率均较小, 大凉山断裂以左旋滑动亏损为主, 马边-盐津断裂具有很弱的左旋和挤压滑动亏损分量并在震后均稍有增强, 会泽-彝良断裂以挤压滑动亏损为主、兼有右旋滑动亏损, 汶川地震后其右旋分量消失.结合其他方法的研究结果, 认为目前这3条断裂带仍具有较大地震发生的危险性.

... 赵静等, 2014, 2015)必须要区分断层的上下盘, 且同1条断层的上下盘不能随深度发生改变, 因此将NW段断层断面参数设定为NE∠85#cod#x000b0 ...

... 赵静等, 2014, 2015) ...

2001

0.0

周荣军, 何玉林, 黄祖智, 等. 2001. 鲜水河断裂带乾宁—康定段的滑动速率与强震复发间隔[J]. 地震学报, 23(3): 250—261.

ZHOU

Rong-jun

, HE

Yu-lin

, HUANG

Zu-zhi

, et al. 2001. The slip rate and strong earthquake recurrence interval on the Qianning-Kangding segment of the Xianshuihe fault zone[J]. Acta Seismologica Sinica, 23(3): 250—261(in Chinese).

鲜水河断裂带乾宁—康定段的几何结构比较复杂 ,由雅拉河、色拉哈—康定、折多塘和磨西 4条次级断裂组成 ,历史上曾发生过 1 72 5,1 786和 1 955年 3次 7级以上强震 .本文在断错地貌和年代学 (14 C和 TL )研究结果的基础上 ,确定的鲜水河断裂带乾宁—康定段各分支断裂晚第四纪以来的平均水平滑动速率分别为 :雅拉河断裂 :(2 .0± 0 .2 ) mm/a;色拉哈—康定断裂 :(5.5± 0 .6) mm/a;折多塘断裂 :(3.6± 0 .3) mm/a;磨西断裂 :(9.9± 0 .6) mm/a.历史地震地表破裂、同震位错和古地震资料研究结果表明 ,雅拉河断裂具有上千年的强震复发间隔 ,色拉哈—康定和折多塘断裂强震复发的平均间隔在 2 30～ 350 a,未来百年均不存在强震复发的可能性 ;磨西断裂强震复发间隔在 30 0 a左右 ,上一次的 1 786年 7 级地震距今已达 2 1 3a,未来百年正处于新一轮的强震复发背景之中

... 冉洪流等(2006)对鲜水河断裂带NW段、周荣军等(2001)对鲜水河断裂带乾宁#cod#x02014 ...

2015

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... Wang等(2009)、 Jiang等(2015)利用GPS和InSAR数据反演计算了鲜水河断裂NW段的震间滑动速率和鲜水河#cod#x02014 ...

... 康定之间存在潜在凹凸体(Jiang et al ...

2002

0.0

... McCaffrey, 2002, 2005, 2007 ...

2005

0.0

... McCaffrey, 2002, 2005, 2007 ...

2007

0.0

2004

0.0

... 鲜水河断裂带为当今地学研究的热点断裂, 闻学泽(2000)、 Papadimitriou等(2004)和Wen等(2008)对鲜水河断裂带的地震破裂分段特征进行过细致的研究 ...

... 7以上地震(Papadimitriou et al ...

... 另外, Papadimitriou等(2004)和徐晶等(2013)将雅拉河与折多塘段的断层倾角设置为75#cod#x000b0 ...

... 磨西附近强闭锁区域对应康定段和磨西段高库仑应力积累和增加区(Papadimitriou et al ...

2001

0.0

... 本文依据上述实际地震地质研究资料构建鲜水河断裂带NW段的断层模型, 考虑到本文所用DEFNODE负位错反演程序(Savage et al ...

... 2 最优模型结果本研究所用DEFNODE负位错反演程序的基本原理和使用方法见参考文献(Savage et al ...

2009

0.0

... Wang等(2009)、 Jiang等(2015)利用GPS和InSAR数据反演计算了鲜水河断裂NW段的震间滑动速率和鲜水河#cod#x02014 ...

2008

0.0

... 鲜水河断裂带为当今地学研究的热点断裂, 闻学泽(2000)、 Papadimitriou等(2004)和Wen等(2008)对鲜水河断裂带的地震破裂分段特征进行过细致的研究 ...

... 1816年和1893年至今2个大地震活跃期, 第1个地震活跃期基本造成了整个断裂带的破裂(Wen et al ...

... Wen et al ...

... 中段八美附近强闭锁区域基本能够对应八美附近地震空区(Wen et al ...

2018

0.0

... Zhang等(2018)对鲜水河断裂带NW段、易桂喜等(2015)对鲜水河断裂带康定段的断层面参数进行了研究 ...

... , 2015), 跨断层短水准和基线研究结果表明龙灯坝和老乾宁附近存在强闭锁区(Zhang et al ...

... Zhang等(2018)给出了鲜水河断裂带NW段上侏倭、格篓、虚墟、虾拉坨、沟普、老乾宁等场地建站时地质调查确定的断层倾角和通过小震精定位确定的断层倾角(表1), 并将2种结果进行了对比分析, 确定了断层的地震地质属性, 其中格篓场地2种结果的断层倾向并不一致, Zhang等(2018)认为其主断层面应该为通过小震精定位确定的NE倾 ...

... Zhang等(2018)的研究成果对本文鲜水河断裂带NW段断层三维结构的设置起到了很好的支持作用 ...

... Zhang等(2018)利用1976#cod#x02014 ...

... 乾宁段低b值区(易桂喜等, 2008)和八美段高库仑应力积累区(徐晶等, 2013), 与Zhang等(2018)给出的龙灯坝和老乾宁附近的强闭锁区域也基本一致 ...