岷县漳县强震前的跨断层短临异常及亚失稳状态特征

引用本文

张希, 贾鹏, 刘峡, 徐晶, 万永魁. 岷县漳县强震前的跨断层短临异常及亚失稳状态特征[J]. 地震地质, 2020,42(5): 1205-1217.
ZHANG Xi, JIA Peng, LIU Xia, XU Jing, WAN Yong-kui. CROSS-FAULT SHORT-TERM AND IMPENDING ANOMALIES BEFORE THE MINXIAN-ZHANGXIAN STRONG EARTHQUAKE AND THE CHARACTERISTICS OF META-INSTABLE STATE[J]. SEISMOLOGY AND GEOLOGY, 2020,42(5): 1205-1217. 复制到剪切板

DOI:10.3969/j.issn.0253-4967.2020.05.011
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岷县漳县强震前的跨断层短临异常及亚失稳状态特征

张希¹⁾, 贾鹏¹⁾, 刘峡²⁾, 徐晶¹⁾, 万永魁²⁾

1)中国地震局第二监测中心, 西安 710054

2)中国地震局第一监测中心, 天津 300180

〔作者简介〕张希, 女, 1967年生, 1994年于西安交通大学获计算数学专业硕士学位, 研究员, 从事地壳形变与地球动力学研究, 电话:13669201202, E-mail: 486408007@qq.com。

收稿日期: 2019-10-08 修回日期: 2020-02-24

基金项目: 国家重点研发计划项目(2018YFC150330506)资助

摘要

2013年岷县漳县 M_S6.6地震发生前2~4d, 距震中37~70km的四店、毛羽沟、麻界滩跨断层流动短水准场地观测到以正断层型突跳为主的短临异常, 尤其是四店场地, 变幅高达5.5mm, 异常相当显著。文中对这3处场地所在的西秦岭构造区的跨断层短水准观测资料进行分析, 并结合GPS连续观测数据与小地震活动信息对其异常机理进行探讨。结果表明: 岷县漳县震前数天, 西秦岭构造区跨断层短水准观测显示的断层活动微动态变化量增大、特性明显改变及靠近震区的 “局部化增强”等现象, 符合构造力学实验显示的亚失稳状态特征。

关键词: 岷县漳县地震; 跨断层短水准; 短临异常; 亚失稳状态

中图分类号:P315.2 文献标志码:A 文章编号:0253-4967(2020)05-1205-13

CROSS-FAULT SHORT-TERM AND IMPENDING ANOMALIES BEFORE THE MINXIAN-ZHANGXIAN STRONG EARTHQUAKE AND THE CHARACTERISTICS OF META-INSTABLE STATE

ZHANG Xi¹⁾, JIA Peng¹⁾, LIU Xia²⁾, XU Jing¹⁾, WAN Yong-kui²⁾

1)The Second Monitoring and Application Center, China Earthquake Administration, Xi'an 710054, China

2)The First Monitoring and Application Center, China Earthquake Administration, Tianjin 300180, China

Abstract

2~4 days before the Minxian-Zhangxian M_S6.6 earthquake on July 22, 2013, short-term and impending anomalies dominated by normal fault type abrupt change were observed at mobile cross-fault short-leveling sites, Sidian, Maoyugou and Majietan, within 37~70km from the epicenter, especially at the Sidian site, where the amplitude of the anomaly reached up to 5.5mm. In this paper, based on the analysis of cross-fault short-leveling observations in the western Qinling Mountains tectonic area, where the above three sites are located, and the experimental results of structural mechanics for the existence of meta-instable stress state before fault instability, the anomaly mechanism is discussed, combined with the information of GPS continuous observation and small earthquakes activities. The results show that: 1)Several days before the earthquake, obvious “changes” in the micro-dynamic variation magnitude and characteristics of fault activities were observed, which revealed that the regional stress had changed. New synchronous anomalies occurred at Sidian, Maoyugou and Majietan sites, especially at Sidian site where the anomaly was large in amplitude, and the number and magnitude of the anomalies increased obviously; Moreover, the dynamic distribution of anomalies of the observational curves showed an obvious change process of the characteristics of tectonic fault activities. In the western Qinling tectonic area, the change was mainly dominated by reverse faulting, but this reverse fault type change was not dominant several months before the earthquake, and till a few days before the earthquake, the normal fault type variation was absolutely dominant, which is contrary to the long-term background of the reverse fault favorable for stress concentration in this tectonic area; In addition, temporal variation of trend accumulation rate, which reflects the feature and magnitude of stress-strain accumulation, showed the accumulation firstly slowing down in several months and turning obviously in several days before the earthquake. 2)Obvious anomaly variation was observed at the sites near the earthquake region several days before the earthquake, the crustal stress evolved from “regional change” to “localized enhancement”. During the four observational periods before the earthquake, it was observed that the cross-fault anomalies were gradually concentrated to the local tectonic region where the earthquake occurred, also the grey relativity index which reflects the general trend of fault activities displayed a larger turning magnitude in this local tectonic region; Next, the local fault segment mostly near the epicenter not only maintained the reverse fault type change consistent with the earthquake dislocation, significant accelerating anomalies were also observed at Majietan site, which may be the relatively strong stress concentration position. The auxiliary data of continuous GPS observation and small earthquake activities were also of some supporting significance to above phenomena. The comprehensive analysis shows that the temporal and spatial evolution process of fault activities and anomalies obtained from the cross-fault short-leveling observation in the western Qinling tectonic area before the strong earthquake accorded with the characteristics of meta-stable(deviating from linear stage)-meta-instable state revealed by the structural mechanics experiment.

Keyword: the Minxian-Zhangxian earthquake; cross-fault short-leveling; short-term and impending anomalies; meta-instable state

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0 引言

地震预报要取得防灾减灾实效, 关键在于短临预报。亚失稳是断层失稳前应力由以积累为主转变为以释放为主的最后阶段(马瑾等, 2012, 2014; 马瑾, 2016), 目前所获得的亚失稳现象多来自构造力学实验室。马瑾等(2012)以5° 拐折断层一次黏滑事件中温度场的演化为例, 讨论了震前应力积累、应力-时间过程中偏离线性、峰值后亚失稳3个阶段的不同特点, 指出失稳错动是由断层各部位独立活动向协同化活动的转化过程, 偏离线性阶段是应力释放、协同作用的开始, 亚失稳阶段应力释放已占据优势。任雅琼等(2013, 2016)、卓燕群等(2013)、 Zhuo等(2015)和Ren等(2018)分析了平直、雁列断层进入亚失稳阶段的位移协同化与热场演化特征。此外, 将实验结果应用于野外观测和实际地震研究更具意义。刘冠中等(2012)发现鲜水河断裂NW段跨断层蠕变场地在1997年玛尼M_S7.5地震前出现了断层活动协同化特征; 刘远征等(2014)认为紫坪铺水库的蓄水在2008年汶川M_S8.0大地震发生中具有断层协同化强化作用; 张淑亮等(2016)发现山西临汾台的宽频带倾斜仪在2010年河津M_S4.8地震前记录到类似亚失稳实验结果的图像。然而截至目前, 野外实际观测获得的亚失稳证据仍很有限。

20世纪70— 80年代, 中国地震局在青藏高原东北缘地区建有60多处跨断层流动短水准场地, 以监测断层两盘的垂向相对运动, 每年3、 7、 11月实施观测, 测线长度为数百m至约1km。在测区及其附近发生5.5级以上地震前多观测到异于常态的变化(陈兵等, 2000; 江在森等, 2001; 张希等, 2014a, 2018b), 但短临异常偏少, 也未从亚失稳这一思路上进行研究。 2013年7月22日发生的岷县漳县M_S6.6地震(34.5° N, 104.2° E)是青藏高原东北缘西秦岭构造区自1936年的6$\frac{3}{4}$级与6级地震后83a以来发生的惟一一次6级以上强震。震前2~4d, 在距震中37~70km的四店、毛羽沟、麻界滩场地(图 1, 2)观测到以正断层型变化为主的异常, 与长期逆断的总体特征相反, 四店场地的变幅为5.5mm, 异常相当显著, 如何解释此观测事实是学者们极为关注的问题。本文将对西秦岭构造区的跨断层短水准观测资料进行分析, 并结合GPS连续观测数据与小地震活动信息, 从断层失稳前存在亚失稳应力状态的构造力学实验结果出发, 对其异常机理进行探讨。

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图 1 本研究所涉及的跨断层场地、 GPS连续站、断裂、块体与地震的分布
F₁ 西秦岭北缘断裂; F₂ 临潭-宕昌断裂; F₃ 礼县-罗家堡断裂; F₄ 迭部-白龙江断裂; F₅ 成县盆地北缘断裂; F₆ 文县断裂; F₇ 东昆仑断裂带; F₈ 塔藏断裂Fig. 1 The distribution of cross-fault sites, GPS continuous stations, faults, blocks and earthquakes in this study.

1 地质构造与应力积累背景

西秦岭构造区位于图 1 所示的柴达木-陇西块体的东部, 即陇西块体上, 经东昆仑断裂带东段、塔藏断裂与巴颜喀拉块体相接, 由北至南分布有西秦岭北缘断裂、临潭-宕昌断裂、礼县-罗家堡断裂、迭部-白龙江断裂、成县盆地北缘断裂、文县断裂等多条断裂, 断裂发育与活动的主要外部动力为巴颜喀拉块体的近SE向滑移及其对陇西块体的近NE向推挤, 断裂活动以左旋逆断为主。 2013年岷县漳县M_S6.6地震的发震构造为临潭-宕昌断裂中东段距主断裂约9km的次级断层, 震源深度约20km, 为逆冲兼左旋走滑性质(何文贵等, 2013; 郑文俊等, 2013)。赵静等(2016)对西秦岭北缘断裂两侧GPS资料的负位错反演显示, 断裂中— 西段于1999— 2007年相对闭锁, 2009— 2013年断裂中段的闭锁程度增强; 张希等(2019)联合GPS、区域水准及跨断裂长水准资料, 借助负位错反演和剖面变形分析, 认为西秦岭北缘断裂中段、临潭-宕昌断裂中东段于1999— 2011年期间应力积累显著, 其逆断、左旋特性与地质资料一致, 故此次地震震中两侧的主要断裂段均在震前十几a呈高应力状态, 具备发生强震的条件。

2 跨断层短水准观测揭示的断层活动协同化特征

亚失稳标志着区域应力由积累转为释放, 对其状态的识别不应局限于发震断层和单个台站(马瑾, 2016)。本文以西秦岭构造作为研究区, 回溯跨断层观测反映的断层活动演化特征。

2.1 资料处理与异常识别

(1)研究区内每处观测场地至少包括2个测点, 分别位于断层两盘。图 2 所示的观测曲线统一为下盘测点(如图2b的四店411)相对上盘测点(四店414)的水准高差时序变化, 故曲线向下为逆断层型变化, 向上为正断层型变化。约70%的场地测线两端均为基岩点; 其余约30%的场地受自然条件所限, 一端为基岩点、另一端为土中点, 但点位稳定、干扰少。测线长数百m至约1km, 可反映近场断层活动。通过测线数据可观测到群体性活动特征, 或有多处场地出现同步协同性 “ 异常” 变化, 故有以此数据为基础开展研究和进行地震预测的意义。

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	图 2 岷县漳县地震前典型的跨断层异常观测曲线(用红点标注异常) a 毛羽沟(3— 2); b 四店(414— 411); c 麻界滩(4基— 6基); d 口子门(4— 3)Fig. 2 Typical observational curves of cross-fault anomalies before the Minxian-Zhangxian earthquake.

(2) “ 异常” 指场地活动异于常态, 观测曲线主要表现为加速或转折、尖点突跳等形态特征, 量值上借助二倍均方差准则识别: 对第i期高差dⁱ, 将其之前的高差值序列作为参考序列, 即 {d^k|k=1, 2, …, i-1}, 则1)计算相邻2期差分值的均方差, 看本期相对上一期的差分值绝对值是否达到或超出2倍均方差, 以反映超出正常变幅的异常, 即:

$| d^{i} - d^{i - 1} | \geq 2 \sqrt[]{\frac{1}{i - 2} \sum_{k = 2}^{i - 1} {[d^{k} - d^{k - 1} - \frac{1}{i - 2} \sum_{k = 2}^{i - 1} (d^{k} - d^{k - 1})]}^{2}}$ (1)

2)通过最小二乘配置获得拟合趋势曲线在每个时间点的值{g^k|k=1, 2, …, i-1}, 计算扣除该趋势变化后的均方差, 看本期是否达到或超出2倍均方差, 以凸显观测曲线上升或下降方向的改变或扰动性异常, 即:

$| d^{i} - g^{i} | \geq 2 \sqrt[]{\frac{1}{i - 1} \sum_{k = 1}^{i - 1} {[d^{k} - g^{k} - \frac{1}{i - 1} \sum_{k = 1}^{i - 1} (d^{k} - g^{k})]}^{2}}$ (2)

满足以上2种情况之一则视为异常(张希等, 2018b)。考虑到参考序列的可靠性以及青藏高原东北缘地区5.5级以上地震的发震平均间隔约为5a的情况, 参考序列需有至少5a的观测数据, 若从起测至第i-1期不到5a, 则取前5a的高差值序列作为参考序列; 另外, 若第i期观测未达到或超出之前长期参考序列的2倍均方差, 但达到或超出了之前5a的2倍均方差, 也视为异常, 具有前兆意义。

2.2 断层活动的协同化分析

图 3为岷县漳县震前2012年7月、 11月与2013年3月、 7月13— 21日4期观测的正断层型、逆断层型变化和正断层型、逆断层型异常分布。根据相邻2期的水准高差变化可得到4个月观测间隔期内场地的正断层型((dⁱ-dⁱ^-1)> 0)或逆断层型((dⁱ-dⁱ^-1)< 0)活动特性, 用红色或蓝色三角形标出; 通过2.1节所述方法识别出的异常用红、蓝色方块区别其正断层型((dⁱ-dⁱ^-1)> 0)和逆断层型((dⁱ-dⁱ^-1)< 0)变化特性, 相对于地质上的长期稳定正断、逆断, 属于微动态短期变化。另外, 图 3 还给出观测间隔期内M_L3.0以上地震的分布。

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	图 3 岷县漳县M_S6.6地震前的跨断层短水准异常动态分布 a 2012年7月相对3月; b 2012年11月相对7月; c 2013年3月相对2012年11月; d 2013年7月相对3月Fig. 3 The dynamic distribution of anomalies of cross-fault short-leveling before the Minxian-Zhangxian M_S6.6 earthquake.

西秦岭构造区有16处跨断层场地, 2013年7月因场地被破坏减为15处。图 3 显示, 2012年7月相对3月、 11月相对7月, 逆断层型短期变化场地分别占总场地的9/16、 11/16, 即为多数(逆断层型短期异常场地也是逆断层型短期变化场地); 11月出现的异常较多, 逆断层型也占多数; 2013年3月相对2012年11月逆断层型短期变化、逆断层型短期异常场地分别减少为8/16和2/4, 开始不占优势; 2013年7月13— 21日相对3月, 正断层型短期变化场地首次占多数, 即9/15, 正断层型短期异常场地也首次占大多数, 达4/5。另外, 4期异常从1、 3、 4至5处逐增, 且震前数天有向震区附近集中的现象。

从图 2 所示的异常观测曲线(通过2.1节所述方法识别出的异常用红点标出)来看, 距震中70km、位于临潭-宕昌断裂东端的毛羽沟场地以及距震中50km、位于西秦岭北缘断裂的四店场地, 分别于震前2d和4d观测到正断层型突跳; 距震中37km、位于临潭-宕昌断裂的麻界滩场地于地震前3d观测到逆断层型加速突跳; 口子门场地的观测数据显示3月份先逆断突跳、震前数天回返形成尖点异常(毛集场地亦如此, 图略)。图 2 中, 1995年7月22日永登M_S5.8、 2000年6月6日景泰M_S5.9、 2008年5月12日汶川M_S8.0、 2013年7月22日岷县漳县M_S6.6和2017年8月8日九寨沟M_S7.0地震(以上地震震中见图 1)是研究区及相邻地块、距研究区最近场地300km内全部5.5级以上地震, 若震前2a内识别出异常则标在图上。

为突显震前短临异常, 图 4 绘制了2012年11月— 2013年11月的高差变化(2012年11月统一为0值)。四店、毛羽沟、麻界滩为震前数天观测到的新异常, 其测点均为基岩点, 更为可靠; 口子门、毛集测段一端为基岩点, 另一端为土中点, 但点位稳定, 2013年3— 7月先逆断、后正断, 形成尖点突跳异常。图 3 所标的全部异常都未找到明显的非构造干扰源, 四店的变幅高达5.5mm, 是其中惟一的大幅异常, 其它场地的变幅约为1~2mm, 远大于± (0.2~0.3)mm/km的测量误差。震后数天(部分场地复测)至2013年11月异常均显示出恢复现象。

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	图 4 震前2~4d观测到的跨断层短临异常Fig. 4 Short-term and impending anomalies of cross-fault leveling observed in 2~4 days before the earthquake.

综上分析, 震前4个月的观测资料显示逆断层型变化开始不占优势; 震前数天观测到异常增多且向震区附近集中, 正断层型变化占绝对优势, 揭示断层的活动量提升和局部化增强, 特性更有了较大改变; 加上出现同步正断层型短临突跳的四店、毛羽沟场地正位于前述GPS、区域水准等联立反演所得的中长期断裂闭锁段上, 距震区也较近, 反映出较好的协同化及加速特征。

3 断层活动趋势和应力积累时序变化特征

3.1 灰色关联度指标显示的断层活动趋势变化

灰色关联度指标可反映断裂活动的总体趋势及其动态演变(张希等, 2014a, b)。

设计算区有m处短水准场地, 首先提取各场地的垂向时序累积变化(每期观测高差减去首期观测高差, 突出时间点之间的相对变化, 若跨断层测段超过1条需求均值), 设为 $h_{j}^{t}$ (t=1, 2, …, n; j=1, 2, …, m)。由于各场地条件各异且均为独立观测, 为使场地间具有可比性, 还需扣除其本底活动水平, 所得场地j时刻t无量纲的垂向活动变化量为

$u_{j}^{t} = \frac{h_{j}^{t}}{\frac{1}{n} \sum_{k = 1}^{n} | h_{j}^{k} | + \sqrt[]{\frac{1}{n - 1} \sum_{k = 1}^{n - 1} {[(h_{j}^{k + 1} - h_{j}^{k}) - \frac{1}{n - 1} \sum_{k = 1}^{n - 1} (h_{j}^{k + 1} - h_{j}^{k})]}^{2}}}$ (3)

进而通过多场地加权平均获取综合指标, 即增加与其它场地相似度较高的场地权重、减轻相似度偏低的场地权重, 突出与构造活动相关的共性特征。场地j的灰色关联度权值 $γ_{j}^{0}$ 为

$φ_{l} (t) = \frac{\min_{l} \min_{t} | u_{j}^{t} - u_{l}^{t} | + 0.5 \max_{l} \max_{t} | u_{j}^{t} - u_{l}^{t} |}{| u_{j}^{t} - u_{l}^{t} | + 0.5 \max_{l} \max_{t} | u_{j}^{t} - u_{l}^{t} |}$ (4)

$γ_{j}^{0} = \frac{1}{m - 1} \sum_{l = 1,}^{l} [\frac{1}{n} \sum_{t = 1}^{n} φ_{l} (t)]$ (5)

时刻t的灰色关联度指标值则为 $\sum_{j = 1}^{m} γ_{j}^{0} u_{j}^{t} / \sum_{j = 1}^{m} γ_{j}^{0}$ 。

图 5 为西秦岭构造区截至2017年的灰色关联度指标的时序变化(2018年以后因场地改造、点位被破坏等原因, 有连续观测数据的场地仅剩不到60%), 曲线向下表示逆断层型变化、向上表示正断层型变化; 黑色实线、红色实线分别为西秦岭构造全区、与岷县漳县地震构造关联更强的小块体, 即图3d所示的西秦岭北缘断裂、临潭-宕昌断裂、礼县-罗家堡断裂所围区域的相应指标值。

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	图 5 研究区跨断层灰色关联度的垂向指标曲线Fig. 5 Curve of vertical index of gray relativity for cross-fault deformation in the study area.

图 5 显示岷县漳县震前数天观测到了超出正常波动范围的正断层型转折。分析认为: 1)跨断层观测的数十a仅为地质年代中很小的一段时间, 观测到的正断层型短期变化可能反映了逆断减缓, 且不排除测量误差、气候、冻土等因素的影响, 故曲线呈波动形态, 总体上以逆断下降为主要变化趋势, 与地质资料一致(已扣除个别非构造干扰; 因周期规律性不强, 也无法通过数学计算削弱其波动性)。 2)1995年永登M_S5.8地震前、 2000年景泰M_S5.9地震前后、 2017年九寨沟M_S7.0地震前出现先逆断加速、后正断回返的现象, 3次地震均位于研究区外的相邻地块, 属于青藏高原东北缘统一的左旋逆断构造应力场, 可能反映了孕震应力场的扰动影响, 逆断加速幅度大而正断转折幅度减小, 转折后基本恢复至正常波动范围内。 3)2010年前后出现先逆断加速、后正断转折的变化, 整个研究区的转折幅度比岷县漳县震区所在局部区域更强。鉴于包含研究区的青藏高原东缘有较多跨断层场地于2010年前后出现以加速为主的异常变化, 张希等(2017)认为其反映了青藏高原东缘整体性E移的加速特性, 不排除受到汶川地震影响的可能。 4)岷县漳县地震是研究区起测以来惟一的6级以上强震, 震前数天(即2013年7月)不但变幅显著增大, 还出现与以往数年波动性逆断层型下降不同的正断层型转折, 超出正常波动范围(如图 5 中蓝色虚线框内所示); 震区所在区域的转折幅度明显大于西秦岭构造全区, 即 “ 近强远弱” , 揭示了区域应力的变化及局部化增强特性, 与前述几次异常形态不同。

3.2 趋势累积率反映的应力积累动态变化

陈兵等(2000)提出了趋势累积率指标, 用式(6)计算某跨断层短水准测线长时间尺度的趋势累积率, 反映了一种广义的应力应变累积强度:

$σ = \frac{\sum_{k = 1}^{n - 1} (d^{k + 1} - d^{k}) / (t^{k + 1} - t^{k})}{\sum_{k = 1}^{n - 1} | d^{k + 1} - d^{k} | / (t^{k + 1} - t^{k})}$ (6)

d^k, t^k, k=1, 2, …, n分别为下盘相对上盘的高差观测值和时间序列, σ 为负值和为正值时分别反映了逆断层型和正断层型的变化特性。若该特性与地质背景一致且绝对值较大, 应力积累程度则较高(李媛等, 2016; 张希等, 2018a)。本文针对图 5 中的红线即震区所在构造区域的灰色关联度指标时序变化值, 通过窗长为5a的滑动来获取趋势累积率动态变化, 即对每个观测时刻, 计算该期及之前5a内变化值序列的趋势累积率(图 6)。图 6 中, 曲线基本在零值线以下, 即负值为主, 显示了逆断积累特性, 部分时段出现过积累加速(曲线快速下降或在波动中快速下降), 或累积减缓甚至释放(曲线明显回升或在波动中回升)。永登地震前积累加速, 震后2a松弛调整; 景泰地震后3a经调整后再恢复; 汶川地震前1a加速, 2010年前后先加速后调整恢复; 九寨沟地震前的2015年曾积累加速。而岷县漳县地震前的2011— 2012年没有出现显著的逆断积累加速, 图 6 中的红色虚线框内显示2013年3月累积还明显减缓, 震前数天更是出现了与以往数年 “ 波动性下降” 相反的显著转折性上升, 地震后又逐渐恢复逆断累积特性。

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	图 6 岷县漳县地震所在构造区域的断层形变趋势累积率时序变化Fig. 6 Temporal variation of accumulation rate of fault deformation trend at the tectonic region where the Minxian-Zhangxian earthquake occurred.

4 结合GPS数据、小地震活动信息的综合分析

GPS连续站(图 1)的观测资料显示(马海萍等, 2018; Ma et al., 2018), 岷县漳县地震前约6个月内, 岷县— 陇西、岷县— 清水基线挤压速度减缓, 岷县— 陇西— 武都面应变显示了一定程度挤压减缓, 这与跨断层短水准观测所示震前5~8个月逆断层型变化开始不占优势的特性相符, 且在时间上准同步(跨断层观测间隔4个月, 无法给出准确时间); 玛曲— 岷县(玛曲站位于东昆仑断裂带东段)基线却挤压略增, 可能反映了在巴颜喀拉块体东部对研究区近NE向推挤的外部动力持续作用下, 地震成核过程中断裂闭锁段的总体弱化或 “ 松动” 现象。

震前9~16个月内小地震活动偏远、较为分散(图3a, b); 距M_S6.6地震不到7个月, 发震断层的主断裂发生M_L3.1地震(图3c), 与岷县漳县地震构造关联且空间位置接近(距离仅21.7km), 应是6.6级地震发生前临潭-宕昌断裂闭锁段的部分能量预释放; 震前1d~4个月内(图3d), 小地震增多且向震区靠近, 显示与跨断层观测结果一致的局部化增强特性。

上述跨断层水准观测、 GPS资料和小地震活动显示出时间和特征上的协同性, 综合多种资料分析认为, 自震前约5、 6个月开始, 震区所在构造块体可能处于应力-时间曲线的 “ 偏离线性阶段” , 应力释放与协同作用开始。另外, 图3d显示临潭-宕昌断裂岷县— 麻界滩附近3处场地不仅维持了逆断层型的活动特性, 麻界滩场地还在震前3d观测到显著的逆断层型加速异常(图2c)。该场地跨临潭-宕昌断裂的次级断层, 距岷县漳县地震震中仅37km, 异常特征与该次地震垂向方向逆断错动的特性一致, 符合马瑾等(2014)、任雅琼等(2016)总结的亚失稳过程中不同部位应力变化分异, 某些部位(多在断层拐折处或震源区附近)可能出现应力集中加剧或预滑、慢地震事件等的认识, 岷县— 麻界滩附近最靠近震区, 有可能是应力集中相对较强的部位。

5 结论与讨论

马瑾(2016)认为地震存在先兆, 关键在于能否观测到和识别这种先兆。 2013年岷县漳县M_S6.6地震发生前震区所在的西秦岭构造区的跨断层短水准观测结果反映了2个特征:

(1)震前数天观测到断层活动微动态变化量和特性的明显 “ 改变” , 揭示了区域应力存在变化。首先, 异常数量和量值明显增大。震前数月异常增多, 震前数天更甚, 新增四店、毛羽沟、麻界滩场地同步异常, 其中距震中仅50km的四店场地变化剧烈, 是岷县漳县震前1a内出现的惟一大幅异常现象, 反映断裂活动总体变化趋势的灰色关联度指标曲线也显示震前数天变幅明显增大。其次, 从观测曲线异常动态分布来看, 整个研究区出现了从以逆断层型变化为主, 到震前数月逆断层型变化不占优势, 直至震前数天以正断层型变化占绝对优势的 “ 转变” , 与该构造区有利于应力集中的以逆断为主的长期背景相反, 变幅最大的四店场地即表现为正断层型变化特征, 灰色关联度指标显示了超出正常波动范围的正断层型转折, 反映应力应变积累特性、程度的趋势累积率时序变化显示震前几个月先积累减缓、震前数天明显转折。

(2)距震区较近的场地在震前数天出现明显变化, 地壳应力从 “ 区域变化” 向 “ 局部化增强” 演化。震前4期观测所得的跨断层异常向震区所在的局部构造区域逐渐集中, 出现大幅异常的四店场地距震中较近; 灰色关联度指标曲线显示, 震区所在的局部构造区域在震前数天出现的转折幅度更大; 另外, 最靠近震中的局部断裂段在维持与地震错动特征一致的逆断层型变化的基础上, 还出现如麻界滩场地的显著逆断层型加速变化, 可能是由于该区为应力集中相对较强的部位。

结合震前十几a的高应力状态背景, 以及GPS连续观测数据和小地震活动信息的佐证, 本文认为岷县漳县M_S6.6地震前西秦岭构造区跨断层短水准观测所得的断层活动与异常时空演化过程比较符合构造力学实验显示的亚稳态(偏离线性阶段, 震前大约5、 6个月可能开始)— 亚失稳状态特征(震前数天内观测到)。

对于其它地震, 如永登、景泰和九寨沟地震, 其相关水准观测于震前出现过正断层型转折变化, 却没有岷县漳县地震前显著, 是这几次地震均非研究区本地地震, 还是不够接近发震时间(跨断层观测完成于景泰震前3个月、九寨沟震前十几d)所致?要回答好这个问题, 还有待对青藏高原东北缘全区跨断层资料和所有强震震例(测区内还有距本文研究区较远的玉门M_S5.9、民乐-山丹M_S6.1、门源M_S6.4地震)的全面、系统的研究。

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[17]	张希, 唐红涛, 李瑞莎, 等. 2014b. 芦山地震前断层形变的中短期异常及同震影响[J]. 大地测量与地球动力学, 34(2): 1—5. ZHANG Xi, TANG Hong-tao, LI Rui-sha, et al. 2014b. Middle-short-term abnormities of fault deformation before Lushan earthquake and its co-seismic influence[J]. Journal of Geodesy and Geodynamics, 34(2): 1—5(in Chinese). [本文引用:1]
[18]	张希, 唐红涛, 李瑞莎, 等. 2017. 青藏高原东缘构造活动整体加速与2013—2014年强震成组活跃关联分析[J]. 武汉大学学报(信息科学版), 42(7): 975—981. ZHANG Xi, TANG Hong-tao, LI Rui-sha, et al. 2017. Analysis on the relationship between overall acceleration of tectonic activities and group strong earthquakes during 2013-2014 at the eastern margin of Qinghai-Tibet plateau[J]. Geomatics and Information Science of Wuhan University, 42(7): 975—981(in Chinese). [本文引用:1]
[19]	张希, 张四新, 秦姗兰, 等. 2019. 岷县漳县6. 6级地震孕育—发生过程的地形变联合反演分析[J]. 地震研究, 42(1): 40—48. ZHANG Xi, ZHANG Si-xin, QIN Shan-lan, et al. 2019. Associated inversion and analysis for crustal deformation of development process of the Minxian-Zhangxian M_S6. 6 earthquake[J]. Journal of Seismological Research, 42(1): 40—48(in Chinese). [本文引用:1]
[20]	赵静, 牛安福, 李强, 等. 2016. 陇西块体周边断层闭锁程度与滑动亏损特征研究[J]. 地震研究, 39(3): 352—358. ZHAO Jing, NIU An-fu, LI Qiang, et al. 2016. Study on dynamic characteristics of fault locking and fault slip deficit in the faults around the Longxi block[J]. Journal of Seismological Research, 39(3): 352—358(in Chinese). [本文引用:1]
[21]	郑文俊, 袁道阳, 何文贵, 等. 2013. 甘肃东南地区构造活动与2013年岷县-漳县 M_S6. 6地震孕震机制[J]. 地球物理学报, 56(12): 4058—4071. ZHENG Wen-jun, YUAN Dao-yang, HE Wen-gui, et al. 2013. Geometric pattern and active tectonics in southeastern Gansu Province: Discussion on seismogenic mechanism of the Minxian-Zhangxian M_S6. 6 earthquake on July 22, 2013[J]. Chinese Journal of Geophysics, 56(12): 4058—4071(in Chinese). [本文引用:1]
[22]	卓燕群, 郭彦双, 汲云涛, 等. 2013. 平直走滑断层亚失稳状态的位移场协同化特征: 基于岩石数字图像变形相关分析方法[J]. 中国科学(D辑), 43(10): 1643—1650. ZHUO Yan-qun, GUO Yan-shuang, JI Yun-tao, et al. 2013. Slip synergism of planar strike-slip fault during meta-instable state: Experimental research based on digital image correlation analysis[J]. Science in China(Ser D), 43(10): 1643—1650(in Chinese). [本文引用:1]
[23]	Ma H P, Feng J G, Wu S Y, et al. 2018. The analysis of the abnormal characteristics of GPS data before the 2013 Minxian-zhangxian M_S6. 6 earthquake[C]. 2018 2^nd International Workshop on Renewable Energy and Development, IOP Conf. Series: Earth and Environment Science, 153: 062044. doi: 10.1088/1755-1315/153/6/062044. [本文引用:1]
[24]	Ren Y Q, Ma J, Liu P X, et al. 2018. Experimental study of thermal field evolution in the short-impending stage before earthquakes[J]. Pure and Applied Geophysics, 175: 2527—2539. [本文引用:1]
[25]	Zhuo Y Q, Ma J, Guo Y S, et al. 2015. Identification of the meta-instability stage via synergy of fault displacement: An experimental study based on the digital image correlation method[J]. Physics and Chemistry of the Earth Parts A/B/C, 85-86: 216—224. [本文引用:1]

2000

0.0

... 5级以上地震前多观测到异于常态的变化(陈兵等, 2000 ...

... 2 趋势累积率反映的应力积累动态变化陈兵等(2000)提出了趋势累积率指标, 用式(6)计算某跨断层短水准测线长时间尺度的趋势累积率, 反映了一种广义的应力应变累积强度: ...

2013

0.0

何文贵, 郑文俊, 王爱国, 等. 2013. 临潭-宕昌断裂新活动特征与岷县漳县 M_S6. 6地震关系研究[J]. 地震工程学报, 35(4): 751—760.

Wen-gui

, ZHENG

Wen-jun

, WANG

Ai-guo

, et al. 2013. New activities of Lintan-Dangchang Fault and its relations to Minxian-Zhangxian M_S6. 6 earthquake[J]. China Earthquake Engineering Journal, 35(4): 751—760(in Chinese).

The Minxian-Zhangxian M6.6 earthquake,with a focal depth of 20 km,occurred at the boundary of Minxian and Zhangxian counties （34.5°N,104.2°E）,Dingxi city,Gansu Province,at 7：45 CST on July 22,2013.By 8：00 on July 29,1034 aftershocks occurred.Among them,nine above M3.0 include one M5.0～5.9,one M4.0～4.9,and seven M3.0～3.9 earthquakes.The strongest aftershock,which occurred at 9：12 on the date of the mainshock,attained MS5.6.Catastrophic damages caused by this earthquake are mainly attributed to poor residential structures erected by the government during a weak economy.The affected area was more than 10 000 km2 and involved in 6 cities and 13 counties ineluding Dingxi,Baiyin,Tianshui,Longnan,and Gannan Zang and Linxia Hui autonomous prefectures.Residents in Baoji,Hanzhong,Xianyang,Xi＇ an,Chengdu,and Mianyang felt this earthquake.The earthquake occurred at southeastern region of Gansu province,which is covered by very thick loess layer and exhibits complex topography such as steep,highly sloped mountains and crisscrossed ravines.It killed 95 people and injured 1 366.Secondary disasters caused by this earthquake include loess landslides,collapses,and pitfalls.Immediately following the earthquake,the China Earthquake Administration quickly organized field survey teams for seismicity monitoring,intensity studies,earthquake damage assessment,and scientific research,through which the first intensity distribution map of the Minxian-Zhangxian M6.6 earthquake was developed for conditions at 14：00 on July 24.The macroscopic epicenter of this earthquake,with an intensity of Ⅷ degrees,was located at Yongguang and Yongxing villages of Meichuan and Lalu Village of Hetuo.The long axes of intensity circled with an NW strike,in accordance with regional structures.This study discusses the basic parameters of this earthquake such as basic intensity distribution,damage features and seismogenic structure.This earthquake occurred at the eastern margin of the Qinghai-Tibetan Plateau at the intersection of the N-S seismic zone and the Kunlun-Qinling fault zone,which is the tectonic transformation zone between the NWW east-striking Kunlun fault and the northern margin of the western Qinling fault zone.We determined that the Hetuo fault,active since the late Pleistocene,passes through the extreme seismic area.Surface rupture phenomena such as landslides,ground fissures,earthquake pitfalls,sandblasting,and water oozing all exhibited zonal distribution along the Hetuo fault.The focal mechanism of this earthquake is consistent with the Hetuo fault.The strike of the nodal plane Ⅱ is 320° and 301.3°,as reported respectively by the Institute of Geophysics and the Institute of Geology,China Earthquake Administration,which also corresponds to the strike of the Hetuo fault.Moreover,the NE-dipping slip plane reported by the two agencies,51° and 57.3°,respectively,corresponds with the dipping direction of the Hetuo fault.Further,we determined that the Anjia Shan landslide slips laterally along a fault valley striking NW that resembles a long tongue with length and width of 310 m and 30～35 m,respectively.The plunge angel of fault striations on the slip plane is 12°～23°,and the main slip plane corresponds with the fault strike.Therefore,the Hetuo fault is seismogenic fault of the Minxian-Zhangxian M6.6 earthquake,which is a secondary fault,belongs to the Lintan-Tanchang fault zone.Three strong earthquakes above M6.0 have occurred near the epicenter of the Minxian-Zhangxian M6.6 earthquake on the Lintan fault,and two moderate earthquakes have occurred at this site in recent years,which include the Minxian M5.2 on November 13,2003,and the Minxian-Zhuoni M5.0 on September 7,2004.This earthquake represents the most recent activities of the Lintan-Tanchang fault zone.

2013年7月22日7时45分,在甘肃省定西市岷县和漳县交界（34.5°N,104.2°E）发生了一次MS6.6地震,震源深度20 km.截至7月29日8时,甘肃岷县、漳县MS6.6地震共记录到余震1 034次,其中3.0级以上余震9次,包括5.0～5.9级1次,4.0～4.9级1次,3.0～3.9级7次.其中最大余震为发生在7月22日9时12分的MS5.6地震.地震造成95人死亡,1 366人受伤.震区地处青藏高原与西秦岭陇南山地接壤区,黄土覆盖较厚,地形起伏较大,山坡陡峭,沟壑纵横,地震引发了黄土滑坡、崩塌和塌陷等次生灾害.另外,震区经济发展较为落后,房屋结构差,土木结构房屋所占比例较高,抗震性能差,是这破坏较重的主要原因.受灾范围涉及定西市、白银市、天水市、陇南市、甘南藏族自治州和临夏回族自治州等6个市（州）13个县,面积约1万多km2.甘肃天水、兰州、陇南、白银,陕西的宝鸡、汉中、咸阳、西安及四川成都、绵阳等地都有震感.地震发生后,中国地震局迅速组织地震现场考察队赶赴灾区,进行震情监测、烈度评定、震害损失评估和科学考察等工作,并于7月24日14时发布了甘肃岷县漳县6.6级地震烈度图.本次地震宏观震中位于岷县梅川镇永光、永星村和禾驮乡的拉路村一带,极震区烈度为Ⅷ度.烈度长轴走向为北西向,与区域构造线相一致.本文归纳总结了岷县、漳县MS6.6地震的基本参数、烈度分布、震害特征和发震构造背景等基本特征.本次地震发生在青藏高原东缘的甘东南地区,该区是南北地震带与昆仑山—秦岭断裂带等活动构造交汇部分部位,也是北西西向的东昆仑断裂与西秦岭北缘断裂之间的构造转换区.地震发生在靠近临潭—宕昌断裂一侧.通过野外地质调查,发现通过极震区有一条断层,即禾驮乡断层为活动断层,为晚更新世活动断层.包括滑坡、地裂缝、地震陷坑和喷沙冒水等地表破坏现象沿断层成带状分布.在震源机制解方面,且震源机制解也与该断层相吻合.中国地震局地球物理研究所给出节面Ⅱ走向为320°,与禾驮乡断层相一致.中国地震局地质研究所给出的是301.3°,也基本与其吻合.两个单位所给出的滑动面倾向为51°和57.3°,皆为向北东倾,与禾驮乡断层倾向也相一致.另外发现安家山滑坡长约310m,宽约30 ～ 35 m,沿断层谷地呈长舌形向北西做水平滑动,滑动面上擦痕侧俯角为12°～23°,主滑动面走向与断层走向相一致.说明禾驮乡断层为此次地震的发震断层,该断层属于区域上临潭—宕昌断裂的次级断层,该断裂历史上在本区内曾发生过3次6级以上强震,近期又发生过2003年11月13日岷县5.2级地震和2004年9月7日岷县—卓尼5.0级地震.此次地震是临潭—宕昌断裂进一步活动的结果.

... 6地震的发震构造为临潭-宕昌断裂中东段距主断裂约9km的次级断层, 震源深度约20km, 为逆冲兼左旋走滑性质(何文贵等, 2013 ...

2001

0.0

... 江在森等, 2001 ...

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. Analysis on the fault activities around the Qilian Mountains before the Menyuan M_S6. 4 earthquake in 2016[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。

... 若该特性与地质背景一致且绝对值较大, 应力积累程度则较高(李媛等, 2016 ...

2012

0.0

... 刘冠中等(2012)发现鲜水河断裂NW段跨断层蠕变场地在1997年玛尼M_S7 ...

2014

0.0

... 刘远征等(2014)认为紫坪铺水库的蓄水在2008年汶川M_S8 ...

2018

0.0

... 4 结合GPS数据、小地震活动信息的综合分析GPS连续站(图 1)的观测资料显示(马海萍等, 2018 ...

2016

0.0

... 马瑾, 2016), 目前所获得的亚失稳现象多来自构造力学实验室 ...

... 2 跨断层短水准观测揭示的断层活动协同化特征亚失稳标志着区域应力由积累转为释放, 对其状态的识别不应局限于发震断层和单个台站(马瑾, 2016) ...

... 5 结论与讨论马瑾(2016)认为地震存在先兆, 关键在于能否观测到和识别这种先兆 ...

2014

0.0

... 亚失稳是断层失稳前应力由以积累为主转变为以释放为主的最后阶段(马瑾等, 2012, 2014 ...

... 该场地跨临潭-宕昌断裂的次级断层, 距岷县漳县地震震中仅37km, 异常特征与该次地震垂向方向逆断错动的特性一致, 符合马瑾等(2014)、任雅琼等(2016)总结的亚失稳过程中不同部位应力变化分异, 某些部位(多在断层拐折处或震源区附近)可能出现应力集中加剧或预滑、慢地震事件等的认识, 岷县#cod#x02014 ...

2012

0.0

... 亚失稳是断层失稳前应力由以积累为主转变为以释放为主的最后阶段(马瑾等, 2012, 2014 ...

... 马瑾等(2012)以5#cod#x000b0 ...

2013

0.0

任雅琼, 刘培洵, 马瑾, 等. 2013. 亚失稳阶段雁列断层热场演化的实验研究[J]. 地球物理学报, 56(7): 2348—2357.

REN

Ya-qiong

, LIU

Pei-xun

, MA

Jin

, et al. 2013. Experimental study on evolution of thermal field of an echelon fault during the meta-instability stage[J]. Chinese Journal of Geophysics, 56(7): 2348—2357(in Chinese).

Detecting earthquake precursors is a difficult topic of earthquake prediction at home and abroard. Carrying out rock deformation experiments in the laboratory and observing the evolution of the characteristics and the laws of the related physical parameters is fundamental and important to the exploring of earthquake precursors. In this study, a sample of compressive en echelon fault set was used to perform the deformation experiment. An infrared thermal image system recorded the temperature variations of the rock samples during the deformation stage. The deformation stage of precursory significance is divided into a strongly-deviation-from-linearity stage, meta-instability stage and instability stage based on the stress-time curve. The purpose of this article is to study the spatial and temporal variations of the thermal field in each stage especially the meta-instability stage and summarize the possible precursory phenomena. The experimental results show that: The temperature in the jog area increases because of compressive stress state during the strong-deviation-from-linear stage; the region of temperature increase moved to the faults from the jog area and the high temperature points on the faults spread and connect due to the converting of fault dislocation from local to overall during the stage of meta-instability, and synergy of temperature increase on the faults and synergy of temperature decrease in between the faults (including the jog area) are two important signals before the instability; The temperature of the whole sample decreases because of stress release except for increasing on the faults caused by friction during the instability stage. In short, there are evident characteristics of thermal field in the stage of meta-instability, which is helpful to identify the meta-instability state; the temperature varies in different deformation staged and different tectonic positions, which means the stage of the deformation and the tectonic position of anomaly should be taken into consideration when we are trying to find thermal anomaly related to the tectonic activity.

Ren Ya-Qiong 1 ;Liu Pei-Xun 1 ;Ma Jin 1 ;Chen Shun-Yun 1 ;

寻找地震前兆是国内外地震预报的难点.在实验室开展岩石变形实验,观测相关物理量的演化特征和规律,是前兆探索中重要的基础工作.本文对压性雁列断层进行变形实验,根据应力时间曲线将具有前兆意义的变形阶段分为强偏离线性阶段、亚失稳阶段和失稳阶段,利用红外热像仪记录各个阶段的热场变化,特别是亚失稳阶段的热场表现.研究结果显示:强偏离线性阶段,岩桥区挤压升温;亚失稳阶段,断层带增温,且高温点扩展连通,断层带内侧卸载降温,断层带上的协同化增温和断层带内侧(包含岩桥区)的协同化降温是失稳前的重要信号;失稳阶段,应力释放,标本整体降温,只有断层带因摩擦升温.总之,亚失稳阶段的热场具有明显特征,利于识别出亚失稳态;不同变形阶段、不同构造部位温度变化不同,在寻找与构造活动相关的热异常时,应考虑变形所处的阶段及异常所处的构造部位.

... 任雅琼等(2013, 2016)、卓燕群等(2013)、 Zhuo等(2015)和Ren等(2018)分析了平直、雁列断层进入亚失稳阶段的位移协同化与热场演化特征 ...

2016

0.0

任雅琼, 马瑾, 刘培洵, 等. 2016. 平直断层黏滑过程热场演化及失稳部位识别的实验研究[J]. 地震地质, 38(1): 65—76. doi: 103969/j.issn.0253-4967.2016.01.005.

REN

Ya-qiong

, MA

Jin

, LIU

Pei-xun

, et al. 2016. Experimental study of temperature evolution and identification of instability position of planar strike-slip fault during process of stick-slip[J]. Seismology and Geology, 38(1): 65—76(in Chinese).

Stick-slip of fault in laboratory accompanies change of temperature. Temperature change is not only concerned with sliding friction, but also with the stress state of the sample. In this article, we use infra-red thermal imaging system as wide-range observation means to study the temperature variation of different stages during the deformation of sample. The rock sample for the experiment is made of granodiorite from Fangshan County with a size of 300mm×300mm×50mm. It is cut obliquely at an angle of 45°, forming a planar fault. Two-direction servo-control system was used to apply load on the sample. The load in both directions was forced to 5MPa and maintained constant (5MPa) in the X direction, then the load in the Y direction was applied by a displacement rate of 0.5μm/s, 0.1μm/s and 0.05μm/s successively. The left and below lateral of the sample were fixed, and the right and top lateral of the sample were slidable when loaded. The experiment results show not only the temperature change from increase to decrease caused by conversion of stress accumulation to relaxation before and after the peak stress, but also opposite variation of temperature increase on fault and temperature decrease in rock during instability stage. Most important of all, we have found the temperature precursor identifying the position of instability through the temperature variation with time along the fault. It shows that rate of temperature increase of instability position keeps relative high value since the stage of strongly off-linear stage, and accelerates in stage of meta-instability. After separating the effect of friction and stress, we found that temperature increase occurs in the rock near the fault instead of on the fault, which means the mechanism of temperature increase is stress accumulation. Temperature of fault at the instability position does not increase, which means the position is locked. We speculate that the position of locked area on fault with high stress accumulation near the fault may be the future instability position. It is of significance of studying temperature variation during stick-slip to the monitoring of earthquake precursors. Heat caused by friction of earthquake needs long time to transfer to the surface and could not be detected as a precursor. While the stress of surface rock near the fault would change as the stress of interior rock changes, which could cause detectable temperature variations. The research purpose of this article is to find special change positions before instability. As the temperature variations are caused by stress and slip of fault, the results are also meaningful to analysis of stress and displacement data related to earthquake precursors.

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

实验室断层黏滑伴随有温度变化,温度不但与摩擦滑动有关,还与样本的应力状态相关。文中利用红外热像仪进行全场观测,研究平直断层黏滑不同阶段的热场演化。实验不仅观测到了峰值前后从应力积累转变为释放导致的温度由升转降的现象,还观测到了失稳后断层升温和块体降温的相反变化。更重要的是通过分析沿断层各个部位的温度随时间的变化,发现了识别失稳部位的温度前兆:失稳部位的温度从强偏离线性阶段开始,一直是相对高值,在亚失稳阶段升温速率突然增大,远高于其他部位。分离摩擦和应力的作用后,发现亚失稳阶段失稳部位的升温发生于围岩上而非断层带上,说明断层处于闭锁状态而相邻的围岩区域处于应力集中状态,推测满足这2个条件的部位可能是未来的失稳部位。此现象或许有助于野外发震位置的判断。

... 任雅琼等(2013, 2016)、卓燕群等(2013)、 Zhuo等(2015)和Ren等(2018)分析了平直、雁列断层进入亚失稳阶段的位移协同化与热场演化特征 ...

2016

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张淑亮, 李艳, 王霞, 等. 2016. 亚失稳态野外观测证据[J]. 吉林大学学报(地球科学版), 46(2): 603—609.

ZHANG

Shu-liang

, LI

Yan

, WANG

Xia

, et al. 2016. Outdoor observation evidence of the meta-instability state[J]. Journal of Jilin University(Earth Science Edition), 46(2): 603—609(in Chinese).

The similar image of rock rupture process was recorded clearly in laboratory by the broadband tiltmeter of Linfen station before the 2010 Hejin M S 4.8 earthquake.In 2009, the observation data from April to July, were based on almost all linear variation; Nonlinear variation deviating linear appeared in August; Data began to drop slowly after the peak reaches in October, and that is a stage of sub-instability; Data appeared quick drop in December and turned flat on Dec.21. 35 days later, the earthquake of M S 4.8 occured 89 km away from the observation station. In the stage of quasi-linear (stress accumulation stage of rock rupture test), seismogenic fault and Benioff strain curve accelerated at the same time, indicating that the sub-instability phenomena recorded by VP-type broadband tiltmeter of Linfen station was from the hypocenter. The sub-instability can be proved through outdoor observation data.

1. Earthquake Administration of Shanxi Province, Taiyuan 030021, China; 2. National Continental Rift Valley Dynamics Observatory of Taiyuan, Taiyuan 030025, China; 3. Linfen Central Seismostation, Earthquake Administration of Shanxi Province, Linfen 041000, Shanxi, China

2010年1月24日,山西省河津市发生了 M S 4.8级地震,在此之前,山西临汾地震台VP型宽频带倾斜仪2009年的观测数据清晰地记录到与实验室岩石破裂失稳过程类似的图像:4-7月观测数据以准线性变化为主;8月出现偏离线性的非线性变化;10月达到峰值点之后开始缓慢下降,此阶段即亚失稳阶段;12月出现加速下降;12月21日转平。转平之后35 d距离观测台站89 km处的河津市即发生了 M S 4.8级地震。在准线性阶段(岩石破裂实验的应力积累阶段),发震断层及附近的Benioff应变曲线也出现同步加速现象。这表明临汾地震台VP型宽频带倾斜仪所记录的亚失稳态现象是来自震源的信息。实验室观测到的亚失稳现象可在野外观测数据中得以验证。

... 张淑亮等(2016)发现山西临汾台的宽频带倾斜仪在2010年河津M_S4 ...

2018

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... 张希等, 2018a) ...

2018

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... 张希等, 2014a, 2018b), 但短临异常偏少, 也未从亚失稳这一思路上进行研究 ...

... 满足以上2种情况之一则视为异常(张希等, 2018b) ...

2014

0.0

... 张希等, 2014a, 2018b), 但短临异常偏少, 也未从亚失稳这一思路上进行研究 ...

... 1 灰色关联度指标显示的断层活动趋势变化灰色关联度指标可反映断裂活动的总体趋势及其动态演变(张希等, 2014a, b) ...

2014

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张希, 唐红涛, 李瑞莎, 等. 2014b. 芦山地震前断层形变的中短期异常及同震影响[J]. 大地测量与地球动力学, 34(2): 1—5.

ZHANG

, TANG

Hong-tao

, LI

Rui-sha

, et al. 2014b. Middle-short-term abnormities of fault deformation before Lushan earthquake and its co-seismic influence[J]. Journal of Geodesy and Geodynamics, 34(2): 1—5(in Chinese).

Based on computation of grey relation degree，using observation data of mobile crossfault deformation up to May 2013，new synthetic norms for striketensilevertical activity parameters of Xianshuihe，Longmenshan and Anninghe fractures，within radius of 300 km from the Lushan earthquake，are given，in order to search for the possible middleshortterm abnormities and timespace features，analyze coseismic deformation or influence.The results show that，1）About a few months to one year before the Lushan earthquake，at the region within radius of 300 km from the epicenter，there existed fault deformation abnormities to some degree，mainly located at the Xianshuihe fracture，Baoxing site of the southern segment of Longmenshan fracture and the vicinity of the southern end of Anninghe fracture； The obvious and concentrate turning deformation possibly had shortterm prediction meaning.2）Baoxing site only 26 km away from the epicenter displayed obvious coseismic thrust deformation； Totally the influence from this earthquake to other sites was weaker； Recently continued turning and jumping abnormities of this study area also possibly reflected the relationship with future strong earthquakes to some degree.

The Second Crust Monitoring and Application Center，CEA，Xi’an 710054

利用截止于2013年5月的跨断层流动形变资料，基于灰色关联度，计算了芦山震区周围鲜水河、龙门山、安宁河三大断裂的走滑、水平张压、垂向活动参量等综合指标。结果显示：1）芦山地震前数月至1年左右，断层形变存在异常，异常主要分布于鲜水河断裂、龙门山断裂南段宝兴场地、安宁河断裂南端附近；2）震中距仅26 km的宝兴场地逆断性同震变形相对明显；3）芦山地震对其他场地同震影响总体上不显著；4）研究区目前仍存在持续的转折或突跳异常变化，不排除与未来强震有一定关联性。

... 1 灰色关联度指标显示的断层活动趋势变化灰色关联度指标可反映断裂活动的总体趋势及其动态演变(张希等, 2014a, b) ...

2017

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... 鉴于包含研究区的青藏高原东缘有较多跨断层场地于2010年前后出现以加速为主的异常变化, 张希等(2017)认为其反映了青藏高原东缘整体性E移的加速特性, 不排除受到汶川地震影响的可能 ...

2019

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... 张希等(2019)联合GPS、区域水准及跨断裂长水准资料, 借助负位错反演和剖面变形分析, 认为西秦岭北缘断裂中段、临潭-宕昌断裂中东段于1999#cod#x02014 ...

2016

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... 赵静等(2016)对西秦岭北缘断裂两侧GPS资料的负位错反演显示, 断裂中#cod#x02014 ...

2013

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郑文俊, 袁道阳, 何文贵, 等. 2013. 甘肃东南地区构造活动与2013年岷县-漳县 M_S6. 6地震孕震机制[J]. 地球物理学报, 56(12): 4058—4071.

ZHENG

Wen-jun

, YUAN

Dao-yang

, HE

Wen-gui

, et al. 2013. Geometric pattern and active tectonics in southeastern Gansu Province: Discussion on seismogenic mechanism of the Minxian-Zhangxian M_S6. 6 earthquake on July 22, 2013[J]. Chinese Journal of Geophysics, 56(12): 4058—4071(in Chinese).

Southeast Gansu province along the central-northern portion of the South-North Seismic Belt, the tectonic activities and deformation pattern are closely related to the northeastward growth of the Tibetan Plateau. Complicated structural geometries were controlled by both Eastern Kunlun and West-Qinling Northern Faults, and outward growth of the NE Tibet continuously contributes to the regional active deformation. In recent years, intermediate-strong earthquakes occurred frequently, calling for a detailed analysis. By integrating both structural and historical seismicity studies, and combining geophysical, seismological and field investigations, we conclude that northward indenting and eastward movement along the Eastern Kunlun Fault is the main tectonic stress source, and also it provides the basic setting and mechanism to generate strong earthquakes. Left-lateral slip and its bi-flanking thrusting 'flower structure' of the West-Qinling Northern Fault contributed to the frequent occurrence of intermediate-strong earthquakes along the Lintan-Tanchang fault to the south. Minxian-Zhangxian M(S)6. 6 earthquake on July 22, 2013 along the central-eastern Lintan-Dangchang fault is a consequence of differential activity due to heterogeneous segments.

Zheng Wen-Jun 1 ;Ren Zhi-Kun 1 ;Yuan Dao-Yang 2 ;He Wen-Gui 2 ;Liu Xing-Wang 2 ;Wang Ai-Guo 2 ;Ge Wei-Peng 1,2 ;Min Wei 3 ;Xu Chong 3 ;Li Feng 3,4 ;

位于南北地震带中北段的甘东南地区，其构造变形和构造活动特征与青藏高原向北东方向的扩展密切相关，该地区复杂的构造几何形态主要受控于东昆仑断裂和西秦岭北缘断裂，区域新构造运动主要动力来源于青藏高原向北东的扩展.近年来，甘东南地区中强地震频发，本文主要通过对该地区构造活动特征、历史地震等资料的综合分析讨论，结合地球物理、地震学和野外调查等资料，认为青藏高原东北部东昆仑断裂的向北挤压和向东的运动是该地区构造应力集中的主要原因，也是该地区中强地震的主要孕震环境和机制，而西秦岭北缘断裂的走滑及向南北两侧逆冲“花状构造”是临潭—宕昌断裂带上中强地震频繁发生的一个重要动力因素.2013年7月22日发生在甘肃岷县—漳县的 M S 6.6级地震正好位于临潭—宕昌断裂带中东段上，是该断裂分段不均匀活动的结果.

... 郑文俊等, 2013) ...

2013

0.0

... 任雅琼等(2013, 2016)、卓燕群等(2013)、 Zhuo等(2015)和Ren等(2018)分析了平直、雁列断层进入亚失稳阶段的位移协同化与热场演化特征 ...

2018

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... Ma et al ...

2018

0.0

... 任雅琼等(2013, 2016)、卓燕群等(2013)、 Zhuo等(2015)和Ren等(2018)分析了平直、雁列断层进入亚失稳阶段的位移协同化与热场演化特征 ...

2015

0.0

... 任雅琼等(2013, 2016)、卓燕群等(2013)、 Zhuo等(2015)和Ren等(2018)分析了平直、雁列断层进入亚失稳阶段的位移协同化与热场演化特征 ...