Spatio-temporal characteristics of repeating seismic events in the middle of Tianshan orogenic belt
-
摘要: 基于2009—2017年新疆区域数字地震台网记录的地震波形数据，利用波形互相关技术及主事件定位方法识别并重新定位了新疆天山中段及其周缘的重复地震。以波形互相关系数0.9作为阈值来确定研究区的重复地震事件，统计结果显示3万零181个事件中的1万1 618个为重复地震事件，这些重复地震事件组成了2395组重复地震对和重复地震丛，占总事件数的38.5%。根据重复地震重定位前后地震对之间距离的统计结果推测，该区域的系统定位误差约为5—10 km。进一步结合该区域最新的震源分类结果对不同震源类型重复地震的时空分布特征予以分析，结果显示：重复矿山爆破事件在空间上呈丛集性分布，且其中的93.6%发生于白天，同时呈现季节性发生模式，即爆破多发生于夏季，而冬季较少；而重复构造地震在空间上大多沿断层分布，24小时内呈随机分布的特征，且研究时段内每个月的活动水平相对平稳；重复诱发地震成丛分布于靠近油气田和水库的区域，但其中部分诱发地震的位置与构造地震重叠，发震时间特征与构造地震相似，为随机分布。Abstract: Based on the seismic waveform data recorded in the stations of Xinjiang regional seismic network from 2009 to 2017, the repeating earthquakes in the middle of Tianshan orogenic belt and its periphery in Xinjiang were determined and relocated by using the waveform cross correlation technique and the master event approach. The results show that 11 618 of the 30 181 events are repeating events, which consist of 2395 groups of doublets and clusters, accounting for 38.5% of the total events. According to the statistical results of the distance between doublets before and after repeating events relocation, it is estimated that the system location error in the research area is about 5−10 km. In addition, combined with the latest source classification results in this area, the results show that repeating earthquakes of different source types have different spatial and temporal distribution characteristics. Repeating quarry blasts appear mostly as clusters, 93.6% of them occur during the daytime, and they also exhibit a seasonal pattern with more events in summers and fewer ones in winters. Tectonic earthquakes occurred in various thrust faults in the Tianshan orogenic belt, and occurred randomly at any time, and the monthly frequency of tectonic events is relatively stable during the studied period. Repeating induced earthquake locations indicate that most of them are located near large gas/oil fields and water reservoirs, but some also geographically overlay tectonic earthquakes in some regions. The occurring time characteristics of induced earthquakes are similar to those of tectonic earthquakes, which appears as random distribution within 24 hours.
-
引言
地震动衰减关系的确定是地震安全性评价的重要一步，而地震烈度衰减关系是缺乏强震活动的观测地区地震动衰减关系确定的基础（胡聿贤，1999；俞言祥，汪素云，2006）。各省建立的应急指挥系统可以在地震后对震害进行快速评估，而震害快速评估的基础是本区的地震烈度衰减关系，无论是估计房屋破坏情况，还是经济损失等，首先都需要根据烈度衰减关系估算出地震的影响范围。
诸多研究者针对地震烈度随震源距和震源深度的变化给出了不同的公式（Gutenberg，Richter，1942；Ergin，1969；Brazee，1972）；Howell和Schultz （1975）对前人的工作进行了总结，从地震学的角度导出了烈度随震中距离的衰减关系模型，既椭圆烈度衰减模型；陈达生和刘汉兴（1989）对该模型进行了改进，提出了椭圆长短轴联合衰减模型，该模型可以保证烈度衰减曲线在近场收敛；而远场一般通过补点的方式使衰减曲线收敛，基于此，有研究人员提出了相应的改进模型（高德潜，1996；沙海军等，2004）。
传统的烈度衰减参数一般采用最小二乘法进行计算，即使得误差函数的二范数最小时所对应的反演参数的解。由于地震烈度值受诸多因素影响且烈度等震线的量取不可能十分精确，因此在烈度衰减参数的反演过程中常常存在异常点，而最小二乘法受异常点的影响较大，因此有研究人员提出使用稳健回归方法来反演烈度衰减参数（王晓军等，2012；刘军等，2014）。
郯庐断裂带自被发现起，一直是地学界研究的热点，其中南段（29°—38°N，115°—122°E）是整个断裂带中地震活动性最强的部分，1668年郯城M8.5地震就发生在这一范围内。何奕成等（2018）曾用稳健回归方法对这一区域的烈度衰减关系进行过研究。但是针对郯庐断裂带中南段的速度结构（黄耘等，2011；刘保金等，2015；熊振等，2016）及介质非均匀性（杨从杰等，2016；范小平等，2017）等相关的研究均表明，郯庐断裂带东侧与西侧的介质结构具有较大的差异，因此有必要对断裂带两侧的烈度衰减特性进行单独研究。
遗传算法是一种非线性全局搜索方法，它的优点是全局搜索，无需求导，不依赖于初始模型的选取等（万永革等，1997；王文萍，王庆良，1999；周都民等，1999；吴建平等，2001）。本文提出一种烈度衰减参数反演的新方法，即采用施加模型约束的遗传算法来分别反演郯庐断裂带两侧的地震烈度衰减参数。遗传算法作为一种全局最优化算法，较难对反演结果的稳定性进行评价，本文拟通过自助抽样（Bootstrap）技术多次重复反演过程，对反演结果的稳定性进行评价；此外，将本文结果与第五代地震动参数区划图中东部强震区烈度衰减关系的结果（以下简称“五代图结果”）进行比较，并将断裂带东侧与西侧的结果也进行比较，并分析产生这些差异的可能原因。
1. 数据与方法
1.1 等震线数据
本文沿用“江苏及邻区地震烈度衰减关系”（何奕成等，2018）一文中表1的等震线数据，按照震中位置在郯庐断裂带主断裂东侧或西侧将数据进行分区，其中在断裂带东侧收集到27次地震的54条等震线数据，在断裂带西侧收集到32次地震的66条等震线数据，此处不再给出具体的烈度与等震线数值，只给出断裂带两侧的地震震级和烈度分布，具体参数列于表1，图1给出了研究区参与反演的地震震中分布图。
表 1 郯庐断裂带东西两侧地震震级和烈度分布表Table 1. Distribution of earthquake magnitude and intensity in east and west sides of Tanlu fault zone震级范围 地震次数 烈度值≥Ⅳ的等震线条数 合计 主断裂东测 主断裂西测 东 西 Ⅳ Ⅴ Ⅵ Ⅶ Ⅷ Ⅸ Ⅹ Ⅳ Ⅴ Ⅵ Ⅶ Ⅷ Ⅸ Ⅹ 东 西 MS3.0—3.9 8 10 6 6 0 0 0 0 0 9 7 0 0 0 0 0 12 16 MS4.0—4.9 15 14 9 15 5 0 0 0 0 7 14 4 0 0 0 0 29 25 MS5.0—5.9 2 5 1 1 2 2 0 0 0 1 4 5 3 0 0 0 6 13 MS6.0—6.9 2 1 2 2 1 1 1 0 0 0 0 1 1 0 0 0 7 2 MS7.0—7.9 0 2 0 0 0 0 0 0 0 0 1 2 2 2 2 1 0 10 合计 27 32 18 24 8 3 1 0 0 17 26 12 6 2 2 1 54 66 ![]()
图 1 研究区参与反演的地震震中分布图Figure 1. Epicenter location of earthquakes for inversion in the studied area1.2 烈度衰减参数反演方法
目前应用较为广泛的烈度衰减模型是陈达生和刘汉兴（1989）提出的椭圆长短轴联合衰减模型。本文沿用该衰减模型，其表达式为
$ \begin{split} I{\text{＝}}&a{\text{＋}}bM{\text{－}}{c}_{1}\mathrm{ln}\left({R}_{\mathrm{a}}{\text{＋}}{R}_{0\mathrm{a}}\right){\text{－}}\\ &{c}_{2}\mathrm{ln}\left({R}_{\mathrm{b}}{\text{＋}}{R}_{0\mathrm{b}}\right){\text{－}}{d}_{1}{R}_{\mathrm{a}}{\text{－}}{d}_{2}{R}_{\mathrm{b}}{\text{，}}\\ \end{split} $
(1) 式中：I为地震烈度；M为震级；Ra和Rb分别为烈度为I的椭圆等震线的长半轴和短半轴的长度；R0a和R0b为近场饱和因子，一般可视为常数；a，b，c1，c2，d1，d2为需要求解的反演参数。令Rb＝0，导出长轴方向的衰减公式为
$ \begin{split} {I}_{{\rm{a}}}{\text{＝}}&a{\text{－}}{c}_{2}\mathrm{ln}{R}_{0\mathrm{b}}{\text{＋}}bM{\text{－}}\\&{c}_{1}\mathrm{ln}\left({R}_{\mathrm{a}}{\text{＋}}{R}_{0\mathrm{a}}\right){\text{－}}{d}_{1}{R}_{{\rm{a}}} {\text{；}} \end{split}$
(2) 令Ra＝0，导出短轴方向的衰减公式为
$ {I}_{{\rm{b}}}{\text{＝}}a{\text{－}}{c}_{1}\mathrm{ln}{R}_{0\mathrm{a}}{\text{＋}}bM{\text{－}}{c}_{2}\mathrm{ln}\!\!\!\!{\text{（}}\!{R}_{\mathrm{b}}{\text{＋}}{R}_{0\mathrm{b}}\!{\text{）}}\!\!\!\!{\text{－}}{d}_{2}{R}_{\mathrm{b}}{\text{，}} $
(3) 令式（2）中的Ra＝0，得到Ia＝a－c2lnR0b＋bM－c1lnR0a；令式（3）中的Rb＝0，得到Ib＝a－c1ln（R0a）＋bM－c2ln（R0b）。可以看出，在震中位置附近，Ia＝Ib，即椭圆长短轴联合衰减模型本身即能满足近场约束条件。
传统的烈度衰减关系一般采用最小二乘法来计算烈度衰减模型的参数，本文基于遗传算法，提出一种烈度衰减参数反演的新方法。
This page contains the following errors:
error on line 1 at column 1: Start tag expected, '<' not foundBelow is a rendering of the page up to the first error.
$ \begin{aligned} { G} {\text{＝}} \left[ {\begin{array}{*{20}{c}} \!\!\!\!1&{{g_{11}}}&{{g_{12}}}&{{g_{13}}}&{{g_{14}}}&{{g_{15}}}\!\!\!\!\!\!\\ \!\!\!\!1&{{g_{21}}}&{{g_{22}}}&{{g_{23}}}&{{g_{24}}}&{{g_{25}}}\!\!\!\!\!\!\\ \!\!\!\!\vdots & \vdots & \vdots & \vdots & \vdots & \vdots \!\!\!\!\!\!\\ \!\!\!\!1&{{g_{N1}}}&{{g_{N2}}}&{{g_{N3}}}&{{g_{N4}}}&{{g_{N5}}}\!\!\!\!\!\! \end{array}} \right]{\text{，}} \end{aligned}$
(4) 则式（1）可以表示为d＝Gm，即
$ \left[ {\begin{aligned} {{I_1}}\\ {{I_2}}\\ {{I_3}}\\ \vdots \;\\ {{I_N}} \end{aligned}} \right] {\text{＝}} \left[ {\begin{array}{*{20}{c}} {1}&{{g_{11}}}&{{g_{12}}}&{{g_{13}}}&{{g_{14}}}&{{g_{15}}}\\ {1}&{{g_{21}}}&{{g_{22}}}&{{g_{23}}}&{{g_{24}}}&{{g_{25}}}\\ { \vdots }&\vdots&\vdots&\vdots&\vdots&\vdots \\ {1}&{{g_{N1}}}&{{g_{N2}}}&{{g_{N3}}}&{{g_{N4}}}&{{g_{N5}}} \end{array}} \right]\left[ {\begin{aligned} {{m_1}}\\ {{m_2}}\\ {{m_3}}\\ {{m_4}}\\ {{m_5}}\\ {{m_6}} \end{aligned}} \right]{\text{，}}$
(5) $ {{\varPhi}} \left(m \right) {\text{＝}} \mathop \sum \limits_{i {\text{＝}} 1}^N \left| {{{d}} {\text{－}} {{Gm}}} \right| {\text{.}}$
(6) This page contains the following errors:
error on line 1 at column 1: Start tag expected, '<' not foundBelow is a rendering of the page up to the first error.
$ {I_{\rm{a}}}{\text{＝}} a {\text{－}} {c_2}\ln {{R_{0{\rm{b}}}}} {\text{＋}} bM {\text{－}} {c_1}{\rm{ln}}\left({{R_{0{\rm{a}}}} + 400} \right) {\text{－}} 400{d_1}{\text{，}} $
(7) $ {I_{\rm{b}}} {\text{＝}} a {\text{－}} {c_1}\ln {{R_{0{\rm{a}}}}} {\text{＋}} bM{\text{－}} {c_2}\ln \left({{R_{0{\rm{b}}}} {\text{＋}} 400} \right) {\text{－}} 400{d_2}{\text{.}} $
(8) 令Ia＝Ib，可以得到
$ {c}_{2}\mathrm{ln}{R}_{0\mathrm{b}}{\text{＋}}{c}_{1}\mathrm{ln}\left({R}_{0\mathrm{a}}{\text{＋}}400\right){\text{＋}}{400d}_{1}{\text{＝}}{c}_{1}\mathrm{ln}{R}_{0\mathrm{a}}{\text{＋}}{c}_{2}\mathrm{ln}\left({R}_{0\mathrm{b}}{\text{＋}}400\right){\text{＋}}{400d}_{2}{\text{，}} $
(9) 即
$ {m}_{4}\mathrm{ln}{R}_{0\mathrm{b}}{\text{＋}}{m}_{3}\mathrm{ln}\left({R}_{0\mathrm{a}}{\text{＋}}400\right){\text{＋}}400{m}_{5}{\text{＝}}{m}_{3}\mathrm{ln}{R}_{0\mathrm{a}}{\text{＋}}{m}_{4}\mathrm{ln}\left({R}_{0\mathrm{b}}{\text{＋}}400\right){\text{＋}}400{m}_{6}{\text{.}} $
(10) 反演参数m3，m4，m5，m6还需要满足式（10），即在反演的过程中增加式（10），对反演参数施加模型约束。
一个完整的烈度衰减关系还需要给出反映反演结果不确定性的参数，通常用拟合标准差来表示，即
$ \sigma {\text{＝}} \sqrt {\frac{1}{N}\mathop \sum \limits_{i {\text{＝}} 1}^N {{\left({{{{d}}_{{\rm{obs}}}} {\text{－}} {{Gm}}{_{{\rm{ga}}}}} \right)}^2}{\rm{}}}{\text{，}}$
(11) 式中，dobs为观测数据，mga为反演得到的参数，N为总的观测数据个数。
1.3 反演的稳定性
本文用统计学上较为常用的自助抽样方法（bootstrap），随机从总的观测数据中抽取80%的数据进行反演，然后用余下的数据对反演结果进行检验，以检测反演方法的稳定性。
This page contains the following errors:
error on line 1 at column 1: Start tag expected, '<' not foundBelow is a rendering of the page up to the first error.
$ {\sigma _i} {\text{＝}} \sqrt {\frac{1}{{{N_{20\% }}}}\mathop \sum \limits_{k {\text{＝}} 1}^{{N_{20\% }}} {{\left({{{{d}}_{20\% }} {\text{－}} { {Gm}}{_{{\rm{ga}}{\text{，}}\!\!\!\!i}}} \right)}^2}}{\text{，}} $
(12) This page contains the following errors:
error on line 1 at column 1: Start tag expected, '<' not foundBelow is a rendering of the page up to the first error.
2. 结果
2.1 烈度衰减参数反演结果
使用“江苏及邻区地震烈度衰减关系”一文（何奕成等，2018）表1中的数据，采用1.2节中介绍的反演方法计算郯庐断裂带中南段断裂带东侧和西侧的烈度衰减参数。近场饱和因子R0a和R0b通过回归搜索过程中使得衰减公式的标准差最小的原则来确定，按此原则，断裂带东侧取R0a＝11.5，R0b＝6.3；断裂带西侧取R0a＝11.1，R0b＝5.4。遗传算法交叉率取0.6，变异率取0.01，种群数目断裂带东侧取150，西侧取200，反演过程的拟合标准差σ通过式（11）计算得到。断裂带东侧烈度衰减参数反演结果为me＝[4.990 2，1.162 7，0.981 1，0.924 6，0.004 4，0.003 5]T，即
$ \begin{array}{*{20}{c}} I{\text{＝}}4.990\;2 {\text{＋}} 1.162\;7M {\text{－}} 0.981\;1\ln \left({{R_{\rm{a}}}{\text{＋}} 11.5} \right) {\text{－}} 0.924\;6 \ln \left({{R_{\rm{b}}}{\text{＋}} 6.3} \right){\text{－}}\\0.004\;4{R_{\rm{a}}} {\text{－}} 0.003\;5{R_{\rm{b}}}{\text{，}} \end{array} $
(13) 沿长轴和短轴方向的烈度衰减公式分别为
$ \left\{ {\begin{array}{*{20}{c}} {{\!\!\!\!I_{\rm{a}}}{\text{＝}} 3.288\;4 {\text{＋}} 1.162\;7M {\text{－}} 0.981\;1\ln \left({{R_{\rm{a}}} {\text{＋}} 11.5} \right) {\text{－}} 0.004\;4{R_{\rm{a}}}}{\text{，}}\\ {{\!\!\!\!\!\!\!\!\!\!I_{\rm{b}}} {\text{＝}} 2.594\;0{\text{＋}}1.1627M {\text{－}} 0.924\;6\ln \left({{R_{\rm{b}}} {\text{＋}} 6.3} \right) {\text{－}} 0.003\;5{R_{\rm{b}}}}{\text{，}} \end{array}\qquad \sigma {\text{＝}} 0.453} \right.{\text{，}} $
(14) 断裂带西侧烈度衰减参数反演结果为mw＝[4.247 1，1.315 1，1.017 8，0.885 6，0.004 2，0.003 8]T，即
$ \begin{array}{*{20}{c}} I{\text{＝}} 4.247\;1 {\text{＋}} 1.315\;1M {\text{－}} 1.017\;8\ln \left({{R_{\rm{a}}} {\text{＋}} 11.1} \right){\text{－}} 0.885\;6\ln \left({{R_{\rm{b}}} {\text{＋}} 5.4} \right) {\text{－}} \\0.004\;2{R_{\rm{a}}} {\text{－}} 0.003\;8{R_{\rm{b}}}{\text{，}} \end{array} $
(15) 沿长轴和短轴方向的烈度衰减公式分别为
$ \left\{ {\begin{array}{*{20}{c}} {{\!\!\!\!I_{\rm{a}}} {\text{＝}} 2.753\;6 {\text{＋}} 1.315\;1M {\text{－}} 1.017\;8\ln \left({{R_{\rm{a}}} {\text{＋}}11.1} \right){\text{－}} 0.004\;2{R_{\rm{a}}}}{\text{，}}\\ {{\!\!\!\!\!\!\!I_{\rm{b}}} {\text{＝}} 1.797\;3 {\text{＋}} 1.315\;1M {\text{－}} 0.885\;6\ln \left({{R_{\rm{b}}} {\text{＋}} 5.4} \right) {\text{－}} 0.003\;8{R_{\rm{b}}}}{\text{，}} \end{array}} \right.\qquad \sigma {\text{＝}} 0.490{\text{.}} $
(16) 图2a和图2b分别给出了郯庐断裂带东、西两侧沿长轴和短轴方向的烈度衰减曲线。从图中可以看出，使用本文提出的方法，即使不进行近场补点和远场补点，烈度衰减曲线在近场和远场仍能收敛，说明本文提出的施加模型约束的反演方法是行之有效的。
![]()
图 2 研究区郯庐断裂带东侧（a）和西侧（b）烈度衰减曲线Figure 2. Seismic intensity attenuation curves in east side （a） and west side （b） of Tanlu fault zone in the studied area2.2 反演结果的稳定性
采用1.3节中介绍的方法，随机抽取80%的数据进行反演，用余下20%的数据进行检验，自助抽样试验重复1 000次。郯庐断裂带东西两侧1 000次自助抽样试验所得各参数结果的平均值分别为mebm=[4.906 9，1.143 7，0.950 4，0.907 7，0.003 8，0.002 9]T和mwbm=[4.419 7，1.271 8，1.002 6，0.894 4，0.003 8，0.003 2]T，此结果与2.1节中的反演结果相差不大。图3和图4给出了郯庐断裂带东侧和西侧1 000次自助抽样试验反演结果绘制而成的烈度衰减曲线，图中黑线为1 000次随机抽样试验反演结果绘制的烈度衰减曲线，绿线为1 000次随机抽样结果的平均值，红线为2.1节中的反演结果。从图中可以看出，郯庐断裂带无论是东侧还是西侧，随机抽样试验反演的平均结果（绿线）与所有数据的反演结果（红线）差异均不大，且对于M7.0以下的震级档，除去个别烈度衰减曲线出现一定的偏离，其余结果均相对集中，证明本文的反演方法是相对稳定的。
![]()
图 3 郯庐断裂带东侧长轴方向（a）和短轴方向（b）的自助抽样结果绘制的烈度衰减曲线Figure 3. Seismic intensity attenuation curves along major axis （a） and minor axis （b） in eastside of Tanlu fault zone by a bootstrapping process![]()
图 4 郯庐断裂带西侧长轴方向（a）和短轴方向（b）的自助抽样结果绘制的烈度衰减曲线Figure 4. Seismic intensity attenuation curves along major axis （a） and minor axis （b） in west side of Tanlu fault zone by a bootstrapping processThis page contains the following errors:
error on line 1 at column 1: Start tag expected, '<' not foundBelow is a rendering of the page up to the first error.
3. 结果对比
This page contains the following errors:
error on line 1 at column 1: Start tag expected, '<' not foundBelow is a rendering of the page up to the first error.
![]()
图 5 郯庐断裂带东侧烈度衰减曲线与五代图烈度衰减曲线对比（a） 长轴方向; （b） 短轴方向Figure 5. Comparison of seismic intensity attenuation curves between east side of Tanlu fault zone and fifth generation seismic ground motion parameter zonation map（a） Major-axis direction; （b） Minor-axis direction图6给出了本文反演的郯庐断裂带西侧结果与五代图东部强震区结果的对比，长轴方向和短轴方向的烈度衰减曲线对比结果分别如图6a和图6b所示。从图中可以看出，两者整体衰减趋势也基本一致，但断裂带西侧烈度衰减曲线在各个震级档均略高于五代图结果，但随着震级的增大两者的差距有略微变小的趋势。
![]()
图 6 郯庐断裂带西侧烈度衰减曲线与五代图烈度衰减曲线对比（a） 长轴方向；（b） 短轴方向Figure 6. Comparison of seismic intensity attenuation curves between west side of Tanlu fault zone and fifth generation seismic ground motion parameter zonation map（a） Major-axis direction; （b） Minor-axis direction图7给出了本文反演的郯庐断裂带东西两侧长轴方向（图7a）和短轴方向（图7b）烈度衰减曲线的对比结果。从两幅图中可以看出，断裂带两侧长短轴方向烈度衰减曲线的差异基本是一致的。当M＝3.0时，断裂带东侧的烈度衰减曲线略高于西侧；当M＝4.0时，两者很接近；当M＝5.0且震中距小于200 km时，断裂带西侧烈度衰减曲线略高于东侧，且距震中越近，这种趋势越明显；当M＝6.0时断裂带西侧烈度衰减曲线明显高于东侧，震中附近断裂带西侧的烈度衰减曲线比东侧高出约0.3度。
![]()
图 7 郯庐断裂带东侧与断裂带西侧烈度衰减曲线对比（a） 长轴方向；（b） 短轴方向Figure 7. Comparison of seismic intensity attenuation curves between east side and west side of Tanlu fault zone（a） Major-axis direction; （b） Minor-axis direction4. 讨论与结论
This page contains the following errors:
error on line 1 at column 1: Start tag expected, '<' not foundBelow is a rendering of the page up to the first error.
地震波的速度结构从不同角度反映了地下介质的状态，两者之间存在一定的联系，一般地震波速度越大，其衰减越弱。针对本研究区已有诸多介质三维速度结构的研究成果（黄耘等，2011；刘保金等，2015；熊振等，2016），这些结果表明，郯庐断裂带中南段东侧的地壳速度整体上低于西侧的地壳速度。地震波在地壳中传播的速度越快，表明介质越坚硬、致密，地震波在其中传播时衰减的能量越弱，反映在烈度上即为地震对该区域造成的烈度越强，烈度衰减的越慢。这可能也是本文之所以得出断裂带西侧的烈度衰减曲线大体上高于东侧的衰减曲线的原因。本文的主要结论如下：
1） 提出了一种施加模型约束的遗传算法来反演地震烈度衰减参数，通过令目标函数一范数最小的策略来使反演结果更加稳健，结果表明即使不进行近场和远场补点，烈度衰减曲线仍能收敛。之后，本文通过自助抽样方法对反演结果进行评价，1 000次自助抽样反演结果表明，在M≤7.0的震级档，本文结果是相对稳定的，此外，用自助抽样的反演结果能对未抽样的数据进行检验。
2） 郯庐断裂带两侧的烈度衰减特性存在差异，断裂带西侧整体上高于断裂带东侧，这与研究区衰减结构（Q值的分布）及速度结构是对应的，本质上还是与断裂带两侧本身的介质结构的差异有关。
3） 结合自助抽样结果和表1及图2的数据分布来看，本文反演的郯庐断裂带东侧和西侧的烈度衰减参数在M≤7.0，震中距小于300 km范围内相对可靠。但是应该指出的是，烈度值本身受诸多因素的影响，存在很强的不确定性，本文仅作为烈度衰减参数反演方法的学术探索，结果究竟是否合理，还有待实际数据的进一步检验和证明。
-
![]()
图 5 研究区2009—2017年重复地震重定位前后震中分布图
Figure 5. Geographical distribution of the epicenters before and after relocation in the studied region between 2009 and 2017 （Red circles represent the epicenters after relocation，black circles represent before relocation）
![]()
图 1 研究区1900—2019年M≥5.0 （a）和2009—2019年M1.0—4.9 （b）地震及台站分布图
Figure 1. Distribution of MS≥5.0 earthquakes between 1900 and 2019 （a） and M1.0—4.9earthquakes between 2009 and 2019 （b） as well as the stations in the studied region
![]()
图 2 随机选取的100对相关系数高于0.85的地震对分别在30 s和35 s窗长时得到的波形互相关系数对比（
$ \bar c$ 为平均互相关系数）Figure 2. Comparison of cross correlation coefficient of randomly selected 100 doublets with correlation coefficient higher than 0.85 for 30 s and 35 s window length （
$\bar c $ represents mean cross-correlation coefficient）![]()
图 3 随机选取的100对相关系数高于0.85的地震对在三个滤波频段所得波形互相关系数的对比（
$ \bar c$ 为平均互相关系数）Figure 3. Comparison of cross correlation coefficient of randomly selected 100 doublets with correlation coefficient higher than 0.85 in three filtering bands （
$\bar c $ represents mean cross-correlation coefficient）![]()
图 4 研究区内2009—2017年M＞1.5重复地震、非重复地震及断层分布
Figure 4. Distribution of active faults and the epicenters of MS＞1.5 earthquakes in the studied region between 2009 and 2017 （Red circles stand for clustered events，black circles for non-clustered events）
![]()
图 6 重复地震对重新定位前（a）、后（b）地震对之间距离的统计分布
Figure 6. Statistical distribution of the distance between doublet before （a） and after （b） relocation of repeating earthquakes
![]()
图 7 重复地震24小时内每小时事件频次直方图
Figure 7. Histograms of number of events per hour for repeating earthquakes in 24 hours
![]()
图 8 天山地震带矿山爆破（a）和构造地震（b）的震级-频次分布图
Figure 8. Cumulative occurrence frequency （squares） versus magnitude along with the best-fitting frequency-magnitude distribution （red curve） for quarry blasts （a） and tectonic earthquakes （b）
![]()
图 9 重定位前后矿山爆破（a）、构造地震（b）和诱发地震（c）的空间分布图
三类事件均为震源分类之后的重复地震事件，震源分类后的地震目录引自Tang等（2020），图中色标所表示的重复地震事件白日发生率定义为某区域白天（北京时间10:00:00至21:59:59）发生的重复地震数与全天事件总数的比值
Figure 9. Distribution of classified quarry blasts （a）， tectonic earthquakes （b），and induced earthquakes （c） before and after relocation
Three types of events are repeating events after the source classification，catalogue after source classification is cited from Tang et al （2020）. Color bar represents the percentage of event daytime occurrence，which is defined as the ratio of the number of events occurring during the working hours （from 10:00:00 am to 09:59:59 pm Beijing time） to the total number of the events
![]()
图 10 震源分类之后的矿山爆破（a）、构造地震（b）和诱发地震（c）的24小时地震频次分布［ 包括重复地震和非重复地震，引自Tang等（2020） ］ ，以及重复矿山爆破（d）、重复构造地震（e）和重复诱发地震（f）的24小时地震频次分布直方图
Figure 10. Histograms of number of events per hour for classified quarry blasts （a），tectonic earthquakes （b），and induced earthquakes （c）［ including repeating and non-repeating earthquakes，from Tang et al （2020） ］ ，and repeating quarry blasts （d）， repeating tectonic earthquakes （e），and repeating induced earthquakes （f）
![]()
图 11 震源分类之后的矿山爆破（a），构造地震（b）和诱发地震（c）的月频次随时间变化［ 所有事件，包括重复地震和非重复地震，引自Tang等（2020） ］ 和重复矿山爆破（d）、重复构造地震（e）、重复诱发地震（f）的月频次随时间变化
Figure 11. Time-frequency distributions for classified quarry blasts （a），tectonic earthquakes （b），and induced earthquakes （c） ［ including repeating and non-repeating earthquakes，from Tang et al （2020） ］ ，and repeating quarry blasts （d），repeating tectonic earthquakes （e），and repeating induced earthquakes （f）
-
邓起东,张培震. 2000. 史前古地震的逆断层崩积楔[J]. 科学通报,45(6):650–655. doi: 10.3321/j.issn:0023-074X.2000.06.020 Deng Q D,Zhang P Z. 2000. Colluvial wedges associated with pre-historical reverse faulting paleoearthquakes[J]. Chinese Science Bulletin,45(17):1598–1604.
管树巍,李本亮,何登发,汪新,Suppe J,雷刚林. 2007. 晚新生代以来天山南、北麓冲断作用的定量分析[J]. 地质学报,81(6):725–744. doi: 10.3321/j.issn:0001-5717.2007.06.002 Guan S W,Li B L,He D F,Wang X,Suppe J,Lei G L. 2007. Late Cenozoic active fold-and-thrust belts in the southern and northern flanks of Tianshan[J]. Acta Geologica Sinica,81(6):725–744 (in Chinese).
蒋长胜,吴忠良,李宇彤. 2008. 首都圈地区“重复地震”及其在区域地震台网定位精度评价中的应用[J]. 地球物理学报,51(3):817–827. doi: 10.3321/j.issn:0001-5733.2008.03.022 Jiang C S,Wu Z L,Li Y T. 2008. Estimating the location accuracy of the Beijing Capital Digital Seismograph Network using repeating events[J]. Chinese Journal of Geophysics,51(3):817–827 (in Chinese).
李宇彤,吴忠良,蒋长胜,李广平. 2008. 利用辽宁区域地震台网记录分析“重复地震”[J]. 地震学报,30(4):383–396. doi: 10.3321/j.issn:0253-3782.2008.04.006 Li Y T,Wu Z L,Jiang C S,Li G P. 2008. Analysis on repeating earthquakes recorded by Liaoning Regional Seismograph Network[J]. Acta Seismologica Sinica,30(4):383–396 (in Chinese).
刘建明,李志海,冯雪玲,孔祥燕. 2017. 2012年新源和静6.6级地震前后P波速度结构的演化[J]. 大地测量与地球动力学,37(5):492–496. Liu J M,Li Z H,Feng X L,Kong X Y. 2017. Evolution of P wave velocity structure before and after the Xinyuan-Hejing MS6.6 earthquake in 2012[J]. Journal of Geodesy and Geodynamics,37(5):492–496 (in Chinese).
易桂喜,闻学泽,辛华,乔慧珍,王思维,宫悦. 2013. 龙门山断裂带南段应力状态与强震危险性研究[J]. 地球物理学报,56(4):1112–1120. doi: 10.6038/cjg20130407 Yi G X,Wen X Z,Xin H,Qiao H Z,Wang S W,Gong Y. 2013. Stress state and major-earthquake risk on the southern segment of the Longmen Shan fault zone[J]. Chinese Journal of Geophysics,56(4):1112–1120 (in Chinese).
张培震,邓起东,杨晓平,彭斯震,徐锡伟,冯先岳. 1996. 天山的晚新生代构造变形及其地球动力学问题[J]. 中国地震,12(2):127–140. Zhang P Z,Deng Q D,Yang X P,Peng S Z,Xu X W,Feng X Y. 1996. Late Cenozoic tectonic deformation and mechanism along the Tianshan Mountain,northwestern China[J]. Earthquake Research in China,12(2):127–140 (in Chinese).
周仕勇,许忠淮,韩京,许洪新,努尔尼沙. 1999. 主地震定位法分析以及1997年新疆伽师强震群高精度定位[J]. 地震学报,21(3):258–265. doi: 10.3321/j.issn:0253-3782.1999.03.005 Zhou S Y,Xu Z H,Han J,Xu H X,Nuernisha. 1999. Analysis on the master event method and precise location of the 1997 Jiashi strong earthquake swarm of western China[J]. Acta Seismologica Sinica,21(3):258–265 (in Chinese).
Astiz L,Shearer P M,Agnew D C. 2000. Precise relocations and stress change calculations for the Upland earthquake sequence in southern California[J]. J Geophys Res:Solid Earth,105(B2):2937–2953. doi: 10.1029/1999JB900336
Bohnhoff M,Wollin C,Domigall D,Küperkoch L,Martínez-Garzón P,Kwiatek G,Malin P E. 2017. Repeating Marmara Sea earthquakes:Indication for fault creep[J]. Geophys J Int,210(1):332–339. doi: 10.1093/gji/ggx169
Burchfiel B C,Brown E T,Deng Q D,Feng X Y,Li J,Molnar P,Shi J B,Wu Z M,You H C. 1999. Crustal shortening on the margins of the Tien Shan,Xinjiang,China[J]. Int Geol Rev,41(8):665–700. doi: 10.1080/00206819909465164
Bürgmann R,Schmidt D,Nadeau R M,d'Alessio M,Fielding E,Manaker D,Mcevilly T V,Murray M H. 2000. Earthquake potential along the northern Hayward fault,California[J]. Science,289(5482):1178–1182. doi: 10.1126/science.289.5482.1178
Chaussard E,Bürgmann R,Fattahi H,Nadeau R M,Taira T,Johnson C W,Johanson I. 2015. Potential for larger earthquakes in the East San Francisco Bay area due to the direct connection between the Hayward and Calaveras faults[J]. Geophys Res Lett,42(8):2734–2741. doi: 10.1002/2015GL063575
Ellsworth W L,Beroza G C. 1995. Seismic evidence for an earthquake nucleation phase[J]. Science,268(5212):851–855. doi: 10.1126/science.268.5212.851
Evans K F,Moriya H,Niitsuma H,Jones R H,Phillips W S,Genter A,Sausse J,Jung R,Baria R. 2005. Microseismicity and permeability enhancement of hydrogeologic structures during massive fluid injections into granite at 3 km depth at the Soultz HDR site[J]. Geophys J Int,160(1):389–412.
Frohlich C,Davis S D. 1993. Teleseismic b values;or,much ado about 1.0[J]. J Geophys Res:Solid Earth,98(B1):631–644. doi: 10.1029/92JB01891
Frohlich C,Nakamura Y. 2009. The physical mechanisms of deep moonquakes and intermediate-depth earthquakes:How similar and how different?[J]. Phys Earth Planet Inter,173(3/4):365–374.
Fu B H,Lin A M,Kano K I,Maruyama T,Guo J M. 2003. Quaternary folding of the eastern Tian Shan,northwest China[J]. Tectonophysics,369(1/2):79–101.
Geller R J,Mueller C S. 1980. Four similar earthquakes in central California[J]. Geophys Res Lett,7(10):821–824. doi: 10.1029/GL007i010p00821
Harris D B. 2006. Subspace Detectors: Theory[R]. Livermore: Lawrence Livermore National Laboratory: Internal Report UCRL-TR-222758.
Hatakeyama N,Uchida N,Matsuzawa T,Nakamura W. 2017. Emergence and disappearance of interplate repeating earthquakes following the 2011 M9.0 Tohoku-Oki earthquake:Slip behavior transition between seismic and aseismic depending on the loading rate[J]. J Geophys Res:Solid Earth,122(7):5160–5180. doi: 10.1002/2016JB013914
Hotovec-Ellis A J,Vidale J E,Gomberg J,Thelen W,Moran S C. 2015. Changes in seismic velocity during the first 14 months of the 2004−2008 eruption of Mount St. Helens,Washington[J]. J Geophys Res:Solid Earth,120(9):6226–6240. doi: 10.1002/2015JB012101
Igarashi T,Matsuzawa T,Hasegawa A. 2003. Repeating earthquakes and interplate aseismic slip in the northeastern Japan subduction zone[J]. J Geophys Res:Solid Earth,108(B5):2249.
Kimura H,Kasahara K,Igarashi T,Hirata N. 2006. Repeating earthquake activities associated with the Philippine Sea Plate subduction in the Kanto district,central Japan:A new plate configuration revealed by interplate aseismic slips[J]. Tectonophysics,417(1/2):101–118.
Kubacki T,Koper K D,Pankow K L,McCarter M K. 2014. Changes in mining-induced seismicity before and after the 2007 Crandall Canyon Mine collapse[J]. J Geophys Res:Solid Earth,119(6):4876–4889. doi: 10.1002/2014JB011037
Lengliné O,Marsan D. 2009. Inferring the coseismic and postseismic stress changes caused by the 2004 MW=6 Parkfield earthquake from variations of recurrence times of microearthquakes[J]. J Geophys Res:Solid Earth,114(B10):B10303. doi: 10.1029/2008JB006118
Li L,Chen Q F,Cheng X,Niu F L. 2007. Spatial clustering and repeating of seismic events observed along the 1976 Tangshan fault,North China[J]. Geophys Res Lett,34(23):L23309.
Li L,Chen Q F,Niu F L,Su J R. 2011. Deep slip rates along the Longmen Shan fault zone estimated from repeating microearthquakes[J]. J Geophys Res:Solid Earth,116(B9):B09310.
Luo Y,Schuster G T. 1991. Wave-equation traveltime inversion[J]. Geophysics,56(5):645–653. doi: 10.1190/1.1443081
Marquering H,Dahlen F A,Nolet G. 1999. Three-dimensional sensitivity kernels for finite-frequency traveltimes:The banana-doughnut paradox[J]. Geophys J Int,137(3):805–815. doi: 10.1046/j.1365-246x.1999.00837.x
Matsubara M,Yagi Y,Obara K. 2005. Plate boundary slip associated with the 2003 Off-Tokachi earthquake based on small repeating earthquake data[J]. Geophys Res Lett,32(8):L08316.
Meng L S,Huang H,Bürgmann R,Ampuero J P,Strader A. 2015. Dual megathrust slip behaviors of the 2014 Iquique earthquake sequence[J]. Earth Planet Sci Lett,411:177–187. doi: 10.1016/j.jpgl.2014.11.041
Mogi K. 1962. Study of elastic shocks caused by the fracture of heterogeneous materials and its relations to earthquake phenomena[J]. Bull Earthq Res Inst,40(1):125–173.
Molnar P,Tapponnier P. 1975. Cenozoic tectonics of Asia:Effects of a continental collision[J]. Science,189(4201):419–426. doi: 10.1126/science.189.4201.419
Nadeau R M,McEvilly T V. 1999. Fault slip rates at depth from recurrence intervals of repeating microearthquakes[J]. Science,285(5428):718–721. doi: 10.1126/science.285.5428.718
Nishenko S P,Buland R. 1987. A generic recurrence interval distribution for earthquake forecasting[J]. Bull Seismol Soc Am,77(4):1382–1399.
Rubin A M,Gillard D,Got J L. 1999. Streaks of microearthquakes along creeping faults[J]. Nature,400(6745):635–641. doi: 10.1038/23196
Schaff D P,Richards P G. 2004. Repeating seismic events in China[J]. Science,303(5661):1176–1178. doi: 10.1126/science.1093422
Schaff D P,Waldhauser F. 2005. Waveform cross-correlation-based differential travel-time measurements at the Northern California Seismic Network[J]. Bull Seismol Soc Am,95(6):2446–2461. doi: 10.1785/0120040221
Schaff D P,Waldhauser F. 2010. One magnitude unit reduction in detection threshold by cross correlation applied to Parkfield (California) and China seismicity[J]. Bull Seismol Soc Am,100(6):3224–3238. doi: 10.1785/0120100042
Schmittbuhl J,Karabulut H,Lengliné O,Bouchon M. 2016. Long-lasting seismic repeaters in the Central basin of the Main Marmara fault[J]. Geophys Res Lett,43(18):9527–9534. doi: 10.1002/2016GL070505
Schwartz D P,Coppersmith K J. 1984. Fault behavior and characteristic earthquakes:Examples from the Wasatch and San Andreas fault zones[J]. J Geophys Res:Solid Earth,89(B7):5681–5698. doi: 10.1029/JB089iB07p05681
Scholz C H. 1968. The frequency-magnitude relation of microfracturing in rock and its relation to earthquakes[J]. Bull Seismol Soc Am,58(1):399–415. doi: 10.1785/BSSA0580010399
Shelly D R. 2017. A 15 year catalog of more than 1 million low-frequency earthquakes:Tracking tremor and slip along the deep San Andreas fault[J]. J Geophys Res:Solid Earth,122(5):3739–3753. doi: 10.1002/2017JB014047
Shu L S,Yu J H,Charvet J,Laurent-Charvet S,Sang H Q,Zhang R G. 2004. Geological,geochronological and geochemical features of granulites in the eastern Tianshan,NW China[J]. J Asian Earth Sci,24(1):25–41. doi: 10.1016/j.jseaes.2003.07.002
Spence W. 1980. Relative epicenter determination using P-wave arrival-time differences[J]. Bull Seismol Soc Am,70(1):171–183.
Taira T,Bürgmann R,Nadeau R M,Dreger D S. 2014. Variability of fault slip behavior along the San Andreas fault in the San Juan Bautista region[J]. J Geophys Res:Solid Earth,119(12):8827–8844. doi: 10.1002/2014JB011427
Tang L L,Lu Z,Zhang M,Sun L,Wen L X. 2018. Seismicity induced by simultaneous abrupt changes of injection rate and well pressure in Hutubi gas field[J]. J Geophys Res:Solid Earth,123(7):5929–5944. doi: 10.1029/2018JB015863
Tang L L,Zhang M,Wen L X. 2020. Support vector machine classification of seismic events in the Tianshan orogenic belt[J]. J Geophys Res:Solid Earth,125(1):e2019JB018132.
Tapponnier P,Peltzer G,Armijo R. 1986. On the mechanics of the collision between India and Asia[J]. Geol Soc London Spec Publ,19(1):113–157. doi: 10.1144/GSL.SP.1986.019.01.07
Templeton D C,Nadeau R M,Bürgmann R. 2008. Behavior of repeating earthquake sequences in central California and the implications for subsurface fault creep[J]. Bull Seismol Soc Am,98(1):52–65. doi: 10.1785/0120070026
Wen L X. 2006. Localized temporal change of the Earth’s inner core boundary[J]. Science,314(5801):967–970. doi: 10.1126/science.1131692
Woessner J,Wiemer S. 2005. Assessing the quality of earthquake catalogues:Estimating the magnitude of completeness and its uncertainty[J]. Bull Seismol Soc Am,95(2):684–698. doi: 10.1785/0120040007
Yamashina K I,Nakamura K. 1978. Correlations between tectonic earthquakes and volcanic activity of Izu-Oshima volcano,Japan[J]. J Volcanol Geotherm Res,4(3/4):233–250.
Yamashita Y,Shimizu H,Goto K. 2012. Small repeating earthquake activity,interplate quasi-static slip,and interplate coupling in the Hyuga-Nada,southwestern Japan subduction zone[J]. Geophys Res Lett,39(8):L08304.
Yao D D,Walter J I,Meng X F,Hobbs T E,Peng Z G,Newman A V,Schwartz S Y,Protti M. 2017. Detailed spatiotemporal evolution of microseismicity and repeating earthquakes following the 2012 MW7.6 Nicoya earthquake[J]. J Geophys Res:Solid Earth,122(1):524–542. doi: 10.1002/2016JB013632
Yin A,Nie S,Craig P,Harrison T M,Ryerson F J,Qian X L,Yang G. 1998. Late Cenozoic tectonic evolution of the southern Chinese Tian Shan[J]. Tectonics,17(1):1–27. doi: 10.1029/97TC03140
Yu W C,Wen L X. 2012. Deep-focus repeating earthquakes in the Tonga–Fiji subduction zone[J]. Bull Seismol Soc Am,102(4):1829–1849. doi: 10.1785/0120110272
Yu W C. 2013. Shallow-focus repeating earthquakes in the Tonga-Kermadec-Vanuatu subduction zones[J]. Bull Seismol Soc Am,103(1):463–486. doi: 10.1785/0120120123
Zhang M,Wen L X. 2015. Seismological evidence for a low-yield nuclear test on 12 May 2010 in North Korea[J]. Seismol Res Lett,86(1):138–145. doi: 10.1785/02201401170
下载:
计量
- 文章访问数: 561
- HTML全文浏览量: 301
- PDF下载量: 116
