震源机制一致性的显著性检验方法

郭祥云, 陈学忠, 李艳娥, 隗永刚, 陈丽娟

郭祥云, 陈学忠, 李艳娥, 隗永刚, 陈丽娟. 2019: 震源机制一致性的显著性检验方法. 地震学报, 41(6): 709-722. DOI: 10.11939/jass.20190045
引用本文: 郭祥云, 陈学忠, 李艳娥, 隗永刚, 陈丽娟. 2019: 震源机制一致性的显著性检验方法. 地震学报, 41(6): 709-722. DOI: 10.11939/jass.20190045
Guo Xiangyun, Chen Xuezhong, Li Yan’e, Wei Yonggang, Chen Lijuan. 2019: Significance test of focal mechanism consistency:Taking the foreshock sequence of the MS5.4 Xiuyan earthquake on November 29,1999 as an example. Acta Seismologica Sinica, 41(6): 709-722. DOI: 10.11939/jass.20190045
Citation: Guo Xiangyun, Chen Xuezhong, Li Yan’e, Wei Yonggang, Chen Lijuan. 2019: Significance test of focal mechanism consistency:Taking the foreshock sequence of the MS5.4 Xiuyan earthquake on November 29,1999 as an example. Acta Seismologica Sinica, 41(6): 709-722. DOI: 10.11939/jass.20190045

震源机制一致性的显著性检验方法

基金项目: 中国地震局地球物理研究所基本业务专项(DQJB19B10)和国家重点研发计划(2018YFC1503405)共同资助
详细信息
    通讯作者:

    陈学忠: e-mail:cxz8675@163.com

  • 中图分类号: P315.33

Significance test of focal mechanism consistency:Taking the foreshock sequence of the MS5.4 Xiuyan earthquake on November 29,1999 as an example

  • 摘要: 本文提出用四维空间的欧氏距离DFM来表示不同地震震源机制之间的一致性,并以1975年辽宁海城ML7.3地震序列和1999年辽宁岫岩MS5.4地震序列为例分析了主震与前震和余震的震源机制一致性与DFM值之间的关系,其结果显示,当欧氏距离DFM<50时,两次地震的震源机制接近。为了对若干次地震组成的一组地震的震源机制一致性进行判定,引入了显著性检验方法。根据陈颙提出的震源机制一致性参数K,以符号检验法和统计检验量Z值检验法对岫岩MS5.4地震前小震的震源机制一致性进行了分析,其结果表明,在临近岫岩MS5.4地震前所发生地震的震源机制的一致性显著,置信度可达98%。
    Abstract: This paper selected the Euclidean distance DFM to measure the focal mechanism consistency between different earthquakes, and analyzed the relationship between the consistency of focal mechanism and DFM value taking the 1975 ML7.3 Haicheng earthquake sequence and 1999 MS5.4 Xiuyan earthquake sequence as examples. The result shows that when DFM is below 50 the two focal mechanisms become extremely consistent. In order to determine consistency of a number of focal mechanisms the significance test method is drawn into. According to the consistency parameter K proposed by Chen Y, we investigated the consistency of focal mechanism for small earthquakes prior to the MS5.4 Xiuyan earthquake using sign test and Z test. The result suggests that the focal mechanisms of small earthquakes occurred near the MS5.4 Xiuyan main shock are significantly consistent with each other with confidence of 98%. Therefore the method proposed in this paper can be applied to practical earthquake prediction effectively.
  • 在大震孕育期间,断裂上可能发生小震,断裂两侧地块中也可能发生小震,但后者可能因原来介质中易滑面的方向不规则,在应力作用下所产生的微裂隙方向也不尽相同,因而该处发生的小震的震源机制可能也不相同,且与断裂带上小震的机制不相同;但至大震发生的短临阶段,小震主要分布在断裂带上,在高应力的背景下,其受力方式均相似,因而震源机制也相似。此外,由于它们与主震都是发生在同一断裂上的错动,所以其机制与主震震源机制也相似(郭增建等,1973)。震源机制一致性或是区分前震序列与一般震群的有效途径之一。目前,研究震源机制一致性的方法主要有:P波与S波最大振幅比法(金严等,1976陈颙,1978)、谱振幅相关系数法(Lund,Bӧðvarsson,2002崔子健等,2015)、断层面参数法(陈颙,1978)、主应力轴夹角差法(刁桂苓等,199219942004程万正等,2006李丽等,2015孙丽娜等,2017刘方斌等,2018ab)、最小旋转角法(万永革,2008)、P轴分布集中度法(荣代潞,2014韩晓明,荣代潞,2015)和应力张量非均匀性法(Michael,1991Wiemer et al,2002李金等,2015张致伟等,2015)。这些方法主要着眼于描述震源机制一致性的变化,所得结果几乎都表明强震前中小地震的震源机制具有一致性增强的现象。震源机制一致性的提出始于前震的识别,对于前震的认定,时空范围要求非常严格,前震一般发生在主震前5天以内,距离主震震中20 km以内(陈颙等,2015)。随着研究的深入,震源机制一致性在地震趋势研判中应用越来越广泛,但一直没有明确以下两个问题:一是如何描述两个震源机制之间的一致性程度;二是对于若干次地震组成的一组地震,如何描述其震源机制一致性程度。为此,本文拟着眼于以上两个问题,利用统计显著性检验方法,提出用四维空间的欧氏距离来表示不同地震震源机制之间的一致性,并以1999年11月29日辽宁岫岩MS5.4地震前震序列为例,对震源机制一致性进行深入研究,以期为地震预测研究提供可操作的具体方法。

    由一次地震的震源机制可给出两组节面的走向、倾角、滑动角,以及主应力P轴、T轴和B轴的方位角和俯角。若断层面的走向、倾角、滑动角已知即可确定震源机制,所以可用断层面的走向、倾角、滑动角这3个量来描述两次地震的震源机制一致性。但是,对于中小地震,由于难以确定震源机制的两个节面中哪个是断层面,震源机制节面的走向、倾角、滑动角不便用于描述震源机制一致性。地震是在震源应力场的作用下发生,只要两次地震的震源应力场一致,其震源机制就应当一致,因此可利用震源机制的主应力轴来描述震源机制一致性。由于我国上地壳内受到的应力场以水平向应力为主,该方向应力对中国大陆地震的孕育和发生起着重要作用(郭增建等,1977),所以本文选取震源机制的P轴和T轴来描述震源机制一致性。设φ为方位角,θ为俯角,P轴和T轴的方位角和俯角(φPφTθPθT)对应于四维空间的一个点。这样,每次地震的震源机制可以对应于四维空间的一个点,它们之间的一致性就可以用欧氏距离来描述。对于地震ij,其震源机制之间的欧氏距离为

    ${D_{\rm{FM}}} {\text{=}} \left[ {{{(\phi _P^i {\text{-}} \phi _P^j)}^2} {\text{+}} {{(\phi _T^i {\text{-}} \phi _T^j)}^2} {\text{+}} {{(\theta _P^i {\text{-}} \theta _P^j)}^2} {\text{+}} {{(\theta _T^i {\text{-}} \theta _T^j)}^2}}\right]^{1/2}{\text{,}}$

    (1)

    DFM越小,两个震源机制的一致性越好,当DFM=0时,两个震源机制完全一致。但是,DFM小到什么程度就可以认为两个震源机制具有一致性呢?为了解决这个问题,本文利用1975年2月4日辽宁海城ML7.3地震序列和1999年11月29日辽宁岫岩MS5.4地震序列的震源机制进行分析。前者的震源机制采用顾浩鼎等(1976)的结果,具体列于表1;后者的震源机制采用张萍和蒋秀琴(2001)的结果,具体列于表2。利用表1表2中的资料,按照式(1)计算前震、余震与主震之间的欧氏距离DFM,得到的结果分别列于表1表2中的最后一列。

    表  1  海城ML7.3地震ML≥4.0前震和余震的震源机制(引自顾浩鼎等,1976)及其与主震之间的欧氏距离DFM
    Table  1.  Focal mechanisms for ML≥4.0 foreshocks and aftershocks of the ML7.3 Haicheng earthquake (after Gu et al,1976) and their Euclidean distance DFM value
    序号发震时刻地理坐标ML深度
    /km
    节面Ⅰ节面ⅡPTB DFM
      年-月-日 时:分:秒东经/°北纬/°走向/°倾角/°滑动角/°走向/°倾角/°滑动角/°方位角/°俯角/°方位角/°俯角/°方位角/°俯角/°
    11975-02-0407:50:47.0122.7540.674.7171108525.1 1765174.5 6115 1572230064 18.85
    21975-02-0410:35:35.0122.7840.674.3151098622.1 1768175.7 6113 1551829768 15.66
    31975-02-0419:36:06.0122.8040.657.31229081−15.2 2375−170.7 6617.5157 410072.50
    41975-02-0501:01:45.0122.9340.704.410298884.020886178.02522 343 414386 17.67
    51975-02-0502:56:29.0122.8240.674.510112886.0 2284178.0 663 157 631083 14.64
    61975-02-0512:33:00.0122.7740.684.1101266111.522180150.526828 17113 5959 29.52
    71975-02-0523:52:54.0122.6340.704.610125645.621785153.926422 16814 4764 23.77
    81975-02-0605:43:42.0122.9040.625.22329287−2.0 2288−177.0 673 338 023186 15.11
    91975-02-0612:24:57.0122.5040.805.4171628034.625956167.929531 351614954 132.71
    101975-02-0613:56:16.0122.8340.754.01011680−128.9 1440−15.716941 562530438 147.66
    111975-02-0802:30:23.0122.4740.824.01216178−31.826259−166.029338 371814848 131.25
    121975-02-1220:42:46.0122.7840.704.0 714352−118.2 346−58.917168 73 334122 143.64
    131975-02-1521:08:02.0122.7840.705.4121118426.2 1864173.3 6214 1582230363 18.79
    141975-02-1622:01:26.0122.8040.685.311123626.8 3084151.826015 16324 2062 25.26
    151975-02-1818:51:49.0122.6540.774.2171144414.5 1480133.125223 14239 542 38.94
    161975-02-2215:45:14.0122.7340.704.0121138536.2 1954173.8 6021 1622930054 26.42
    171975-02-2405:07:20.0122.8840.784.4 713257−52.925848−132.927860 17 511030 149.77
    181975-02-2504:52:10.0122.6240.734.41413474−4.222686−164.027614 180 8 6274 159.93
    191975-02-2605:09:53.0122.8240.674.3 81219020.021070180.025414 3471412170 16.62
    201975-03-2111:32:59.0122.9540.774.01126072−29.6 062−159.5 3834 132 723156 41.11
    211975-03-2923:16:36.0122.6040.774.1 61118524.1 1966174.5 6313 1582030365 16.92
    221975-04-1003:55:37.0122.4840.724.610118859.0 2781184.92533 1631035780 18.20
    231975-04-2100:17:06.0122.4540.774.0 81098430.2 1660173.1 5917 1572529959 22.14
    241975-07-0407:06:29.0122.6740.724.11013756−19.423974−144.428336 18512 8052 157.73
    下载: 导出CSV 
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    表  2  岫岩MS5.4地震MS≥4.0前震和余震的震源机制解(引自张萍,蒋秀琴,2001)及其与主震之间的欧氏距离DFM
    Table  2.  Focal mechanisms for MS≥4.0 foreshocks and aftershocks of the MS5.4 Xiuyan earthquake (after Zhang,Jiang,2001) and their Euclidean distance DFM value
    序号发震日期地理坐标MS深度
    /km
    节面Ⅰ节面ⅡP T B DFM
      年-月-日 时:分:秒东经/°北纬/°走向/°倾角/°滑动角/°走向/°倾角/°滑动角/°方位角/°俯角/°方位角/°俯角/°方位角/°俯角/°
    11999-11-0907:01:40.6123.0340.534.19320707.522883159.8261263581120870159.33
    21999-11-0907:07:21.2123.0240.534.2813780−7.122883−169.9 6218331 3 8477158.79
    31999-11-2520:47:48.5123.0040.554.081374429.5 2770130.0 5625150 8 113839.46
    41999-11-2520:55:4.2123.0040.554.491394230.7 2770127.72711216746 123642.50
    51999-11-2623:34:01.0123.0240.534.491107010.6 2480159.72461515212 466717.00
    61999-11-2912:10:39.2123.0340.535.4929684−20.1 2870−173.6 624119136280700
    71999-11-2912:45:50.4123.0340.535.1930070173.62068420.1 1240262221936811.36
    81999-11-2916:16:47.6123.0340.535.081118020.3 1770169.424820341 83246716.52
    91999-11-3007:52:55.8123.0340.534.091116813.0 1578157.526232162153486524.78
    101999-11-3013:58:17.7123.0340.535.2929180−16.3 2674−169.627015180 2260709.33
    111999-11-3014:06:55.1122.9840.554.982927210.519780161.7 4122133101667018.25
    121999-11-3014:09:36.6123.0240.554.391125811.8 1680147.4 7728350 33575720.22
    131999-11-3020:19:44.2123.0340.534.3929583−20.2 2870−172.529325 3725279704.69
    141999-12-0101:47:1.9123.0340.534.292908010.219880169.8 6722338 61547817.03
    151999-12-0104:33:0.5123.0340.534.491108030.5 1460168.4 428274 03076020.71
    161999-12-0112:45:30.8123.0340.554.392997010.620580159.729014 18 21176816.64
    171999-12-1305:49:30.5123.0840.534.111 1376023.3 3670147.9 7942346 2 85238.18
    181999-12-2719:27:15.4123.0240.534.081127010.6 1980159.7 9130 0 93566614.73
    192000-01-1207:43:55.4123.0540.535.5814680−40.725650−166.9 70253331313950140.51
    202000-01-1213:00:31.9123.0340.554.391128826.0 2064177.826913359 12976210.20
    下载: 导出CSV 
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    表1最后一列的DFM值可见:海城ML7.3地震序列MS≥4.0前震和余震的DFM值分布在14—42范围之内的有16次,占69.57%,分布在131—160之内的有7次,占30.43%。两次前震的DFM值分别为18.85和15.55。图1给出了不同DFM值的前震和余震的震源机制图像,同时也给出了海城ML7.3地震的震源机制。可以看出:DFM值分布在14—42之内的地震,其震源机制与主震极为接近;而DFM值分布在131—160之内的地震,其震源机制与主震差别较大。

    图  1  海城ML7.3地震序列的震源机制图像和欧式距离DFM
    Figure  1.  Focal mechanisms and Euclidean distance DFM values of the ML7.3 Haicheng earthquake sequence
    图  1  海城ML7.3地震序列的震源机制图像和欧式距离DFM
    Figure  1.  Focal mechanisms and Euclidean distance DFM values of the ML7.3 Haicheng earthquake sequence

    表2最后一列的DFM值可见:岫岩MS5.4地震序列ML≥4.0前震和余震的欧式距离DFM值分布在4—43之内的有16次,占84.21%;DFM值分布在140—160之内的有3次,占15.79%;临近主震的3个前震的DFM值分别为39.46,42.5和17.0,均在43以下。

    通过上述对两个地震序列的前震和余震的DFM值的分析,我们认识到,与主震震源机制相近的地震的DFM值均在43以下。故对于两次地震而言,其震源机制相近的条件可以适当放宽至DFM<50.

    对于若干次地震组成的一组地震,一般来讲各次地震的震源机制不一致,在这种情况下,可以用其欧式距离DFM平均值确定与某次地震震源机制的一致性,但只能显示一致性的强弱,不能确定是否一致或在多大程度上一致。陈颙(1978)给出了参数K来描述一组地震震源机制的一致性,假设N次地震中震源机制一致的地震次数为n1,不一致地震的次数为n2K定义为

    $K {\text{=}} \frac{{{n_1} {\text{-}} {n_2}}}{N}{\text{,}}$

    (2)

    K在−1到1之间变化,K>0表示震源机制一致的地震比不一致的地震多,但是当K值为多大时一致性才显著尚未解决。本文将N次地震根据DFM值分为两部分,一部分地震的次数为n1DFM>50;另一部分地震的次数为n2DFM≥50;然后,根据式(2)计算K值。当N≤25时,可用符号检验法对一组地震的震源机制是否一致进行统计显著检验;当N≥25时,可采用

    $ Z {\text{=}} \dfrac{{r {\text{-}} 0.5 {\text{-}} \dfrac{N}{2}}}{{\dfrac{{\sqrt N }}{2}}} $

    (3)

    统计检验量Z进行检验(张敏强,2010)。式(3)中:rn1n2两者中的较大者;Z为显著性水平α=5%,2%和1%下的临界值,分别为1.96,2.33和2.58。一般地,如果Z≥1.96,表示能通过α=5%的显著性检验,可以认为这组地震震源机制的一致性显著。

    本文将利用上述方法对岫岩MS5.4地震序列的震源机制与MS5.4主震震源机制之间的一致性进行分析。选取1999年1月至11月岫岩MS5.4主震发生前41次2.5≤ML≤3.9小震的震源机制解(张萍等,2003),其空间分布如图2所示,震源机制解参数列于表3图3给出了这些小震与主震之间DFM值的变化,可见:DFM值集中分布在4—45和84—163这两个区间,前者有30次,后者有11次。在临近主震发生的1999年11月份,共发生21次小震,其中DFM≤45的17次,DFM≥84的4次。按上述方法,以DFM=50将地震进行划分,不会影响结果。

    图  2  岫岩MS5.4地震前小震震源机制解空间分布
    Figure  2.  Spatial distribution of focal mechanisms of small earthquakes occurred prior to the MS5.4 Xiuyan earthquake
    表  3  1999年岫岩MS5.4地震前小震震源机制
    Table  3.  Focal mechanisms for small earthquakes before the MS5.4 Xiuyan earthquake in 1999
    序号发震日期地理坐标 MS深度
    /km
    节面Ⅰ节面ⅡPTB
      年-月-日 时:分:秒东经/°北纬/°走向/°倾向倾角/°走向/°倾向倾角/°方位角/°俯角/°方位角/°俯角/°方位角/°俯角/°
    11999-01-1503:05:18.6122.6240.65 3.411128WS80 42NW62261263581111059
    21999-01-0605:43:10.9122.8240.65 2.910105NE76 17ES80 6218331 323372
    31999-01-2007:37:43.4122.5340.70 3.212101NE80 13ES70 5625150 825965
    41999-04-0916:31:48.0121.0042.00 3.015138WS52 32ES702711216746 1243
    51999-04-2321:13:38.4122.8240.70 2.9 7107WS70 20NW862461515212 1368
    61999-04-2715:14:14.4124.5741.12 2.813125NE85 40ES30 62411913630430
    71999-04-3021:16:13.3122.8539.68 2.7 5142NE78 60NW42 12402622215239
    81999-05-1112:29:25.9122.7840.65 3.414114WS80 27NW7024820341 8 9068
    91999-05-1501:45:46.6122.2239.38 3.110118WS55 35NW802623216215 5052
    101999-05-2220:40:45.1122.4740.73 3.4 9133WS82 46NW8027015180 2 9378
    111999-05-2415:58:35.1122.2041.70 2.528 86NW80 0NE68 41221331024667
    121999-05-2903:13:30.9121.0042.00 3.321119NE70 34ES72 7728350 325364
    131999-06-0301:46:50.2122.2541.67 3.4 8 75NW64164NE9029325 372516464
    141999-06-0616:51:47.4122.8240.65 2.814110NE70 26ES80 6722338 623166
    151999-08-2112:56:25.9121.7041.25 2.721142NE70 45NW70 428274 018361
    161999-08-3115:11:21.0122.2339.35 2.914153WS80 64NW8029014 18 210875
    171999-09-0605:05:30.3122.6740.70 3.1 6114NE58 41ES64 7942346 225247
    181999-09-2013:22:57.0122.6740.68 2.9 5136NE62 52ES76 9130 0 925658
    191999-10-1007:21:15.5122.9540.65 2.8 9109NE59 24ES80 70253331321956
    201999-10-1216:04:20.3122.1840.48 3.414132WS80 46NW8026913359 1 8774
    211999-11-0414:46:26.9122.6039.27 3.5 7118WS57 14ES7015239252 534850
    221999-11-0903:34:1.3121.5738.52 3.9 9114NE62 22ES902703713937 2225
    231999-11-0908:21:36.2123.0040.53 2.9 8118NE70 32ES80 7720345 724067
    241999-11-0917:44:44.6123.0040.53 3.6 8121NE70 34ES80 8020347 823867
    251999-11-1618:57:48.5123.0040.53 3.0 9110NE90 20ES60 61211612129160
    261999-11-1703:09:31.4123.0040.53 2.7 9112WS70 24NW8224920156 9 4370
    271999-11-1723:59:50.8123.0040.55 2.5 9102WS80 14NW8423911148 4 4677
    281999-11-1808:15:41.2123.0040.53 2.8 9111NE80 29ES50 62371672028048
    291999-11-2100:50:1.9123.0040.55 3.0 8122NE72 40ES70 8128172 226564
    301999-11-2500:59:19.2123.0040.55 3.0 8112NE80 32ES42 60391722528340
    311999-11-2521:17:50.8123.0040.53 3.5 8138NE70 55ES70 9630187 127861
    321999-11-2522:08:12.4123.0040.53 3.2 8147WS76 61NW8028518194 2 9273
    331999-11-2523:19:17.5123.0040.55 3.2 8110WS80 24NW7024620338 6 8467
    341999-11-2603:18:23.3123.0040.55 2.7 9123NE72 39ES70 8027171 126361
    351999-11-2623:36:20.7123.0040.53 3.1 9112NE60 38ES60 7740344 325346
    361999-11-2701:33:26.6123.0040.53 2.6 8148WS80 53ES6819221 99 835065
    371999-11-2702:29:43.7123.0040.55 2.8 8122WS74 38NW6826023350 2 9263
    381999-11-2715:48:2.6123.0040.55 3.2 8118WS80 36NW50250373542010747
    391999-11-2808:15:3.6122.9840.55 3.3 8108NE86 20ES62 60211561727961
    401999-11-2905:56:59.9123.0040.55 3.2 9121NE80 31ES47 61371672028146
    411999-11-2909:25:51.2123.0040.53 2.7 8126NE38 44ES86 99373462922660
    下载: 导出CSV 
    | 显示表格
    图  3  1999年岫岩MS5.4地震前各次小震的欧式距离DFM值变化
    Figure  3.  Variation of Euclidean distance DFM values of small earthquakes prior to the MS5.4 Xiuyan earthquake in 1999

    取20次地震为1组,计算其DFM平均值,以2次地震进行滑动,得到DFM平均值随时间的变化,如图4所示。可以看出:DFM平均值从1999年11月中旬开始逐渐下降,临近主震发生前降至最低。尽管这样,DFM平均值与震源机制一致性之间的相关性仍然存疑。

    图  4  1999年岫岩MS5.4地震前欧式距离DFM平均值随时间的变化
    Figure  4.  Temporal variation of average Euclidean distance DFM value prior to the MS5.4 Xiuyan earthquake in 1999

    同样取20次地震为一组,以DFM=50为界,将地震分为两组,然后按式(2)计算K值。以1次地震进行滑动,得到K值随时间的变化,如图5a所示。查阅符号检验表可知,在N=20的情况下:当n1=15时,可以在显著性水平α=5%下通过显著性检验,表示这20次地震的震源机制一致性的置信度可达95%;当n1=17时,可以在显著性水平α=1%下通过显著性检验,表示这20次地震的震源机制一致性的置信度可达99%。从图5a中可以看出:至1999年11月27日,K值达到0.6,超过α=5%的显著性水平检验的临界值;最后,K值达到α=1%显著性水平检验的临界值,即最后20次地震的震源机制一致性的置信度高达99%。

    图  5  1999年岫岩MS5.4地震前K值(a)和Z值(b)随时间的变化
    水平线分别表示通过α=1%,2%和5%的显著性水平检验的临界值
    Figure  5.  Temporal variation of K value (a) and Z value (b) prior to the MS5.4 Xiuyan earthquake in 1999
    Horizontal lines show the critical values at the significance level α=1%,2% and 5%

    取26次地震为一组,按式(3)计算Z值进行检验。以1次地震进行滑动,得到Z值随时间的变化,如图5b所示。可见:在临近主震发生时,Z值最高可达2.55,超过α=2%的显著性水平检验的临界值,即最后26次地震的震源机制一致的置信度超过98%。

    上述分析是在主震震源机制已知的情况下,通过计算前震与主震的欧式距离DFM值而进行的,而在地震预测实际工作中,主震尚未发生,其震源机制未知。这种情况下,可以在已经发生的若干次地震中,选取一次地震的震源机制作为主震的震源机制,计算其它地震与该地震之间的DFM值,再利用上述方法进行分析。表3中最后一次地震与主震之间的DFM值为40,其震源机制与主震一致,若将其震源机制作为主震的震源机制,所得DFM值如图6a所示,可以看出与图4中给出的结果基本一致。而表3中第36次地震与主震之间的DFM值为84,其震源机制与主震不一致,若将其震源机制作为主震的震源机制,所得DFM值如图6b所示,可见与图4中给出的结果相差甚远,因此,若某次主震的前震中有与主震震源机制一致的地震,那么在主震发生前将该地震的震源机制当成主震的震源机制进行分析,所得结果与之后发生的主震得到的结果完全一致。因此,本文提出的方法能较好地应用于实际地震预测。

    图  6  表3中第41号(a)和第36号(b)地震的震源机制分别作为主震的震源机制所得的岫岩MS5.4地震前K值随时间的变化
    Figure  6.  Temporal variation of K value prior to the MS5.4 Xiuyan earthquake taking the focal mechanism of No.41 (a) and No.36 (b) earthquake in Table 3 as that of the main shock

    地震发生的根本原因是应力作用下的岩石破裂。陈颙(1978)发现邢台地震和海城地震前,中小地震的破裂方式趋于一致,也就是说,岩石在高应力背景的作用下,微裂隙的方向基本相同,即中小地震的破裂方式相同,并基于这样的物理认识,提出震源机制一致性可以作为描述地震活动的新参数,即用一组地震震源断层面走向均值的标准偏差,或用震源机制解参数来描述地震机制的一致或混乱程度,以探索孕震区内背景构造应力场的动力学过程。该方法中震源机制一致性参数是个相对的概念。泽仁志玛等(2009,2010)提出用震源机制一致性参数来研究应力场取向的变化,以此来获取构造运动的情况及强震的前兆信息。但该方法需要事先确定背景应力场,因此具有很大的不确定性,而且对于如何描述两个震源机制之间的一致性程度以及对于若干次地震组成的一组地震,如何描述其震源机制一致性程度均无明确的回答。鉴于此本文提出了利用震源机制的P轴和T轴的方位角和俯角来计算两次地震之间的震源机制欧式距离DFM,并分析了1975年辽宁海城ML7.3地震序列和1999年辽宁岫岩MS5.4地震序列的主震与前震和余震的震源机制一致性与DFM值之间的关系。结果表明,当DFM<50时,二者震源机制接近。在此基础上,利用符号检验法和统计检验量Z值检验法对岫岩MS5.4地震前小震的震源机制一致性进行了分析,所得结果表明,在岫岩MS5.4地震前发生的短临地震,其震源机制一致性显著,置信度达98%,故本文提出的方法可以在地震预测实际工作中得以有效应用。当然,本文仅提出了震源机制一致性参数的计算方法及两个震例的研究,具体的震情判断指标尚需进一步研究。下一步如果能在基于应力状态演化的物理背景下结合其它观测手段进行地震预测,将会更加行之有效。这还需要更多震例的研究,或更长时间的检验。

  • 图  1   海城ML7.3地震序列的震源机制图像和欧式距离DFM

    Figure  1.   Focal mechanisms and Euclidean distance DFM values of the ML7.3 Haicheng earthquake sequence

    图  1   海城ML7.3地震序列的震源机制图像和欧式距离DFM

    Figure  1.   Focal mechanisms and Euclidean distance DFM values of the ML7.3 Haicheng earthquake sequence

    图  2   岫岩MS5.4地震前小震震源机制解空间分布

    Figure  2.   Spatial distribution of focal mechanisms of small earthquakes occurred prior to the MS5.4 Xiuyan earthquake

    图  3   1999年岫岩MS5.4地震前各次小震的欧式距离DFM值变化

    Figure  3.   Variation of Euclidean distance DFM values of small earthquakes prior to the MS5.4 Xiuyan earthquake in 1999

    图  4   1999年岫岩MS5.4地震前欧式距离DFM平均值随时间的变化

    Figure  4.   Temporal variation of average Euclidean distance DFM value prior to the MS5.4 Xiuyan earthquake in 1999

    图  5   1999年岫岩MS5.4地震前K值(a)和Z值(b)随时间的变化

    水平线分别表示通过α=1%,2%和5%的显著性水平检验的临界值

    Figure  5.   Temporal variation of K value (a) and Z value (b) prior to the MS5.4 Xiuyan earthquake in 1999

    Horizontal lines show the critical values at the significance level α=1%,2% and 5%

    图  6   表3中第41号(a)和第36号(b)地震的震源机制分别作为主震的震源机制所得的岫岩MS5.4地震前K值随时间的变化

    Figure  6.   Temporal variation of K value prior to the MS5.4 Xiuyan earthquake taking the focal mechanism of No.41 (a) and No.36 (b) earthquake in Table 3 as that of the main shock

    表  1   海城ML7.3地震ML≥4.0前震和余震的震源机制(引自顾浩鼎等,1976)及其与主震之间的欧氏距离DFM

    Table  1   Focal mechanisms for ML≥4.0 foreshocks and aftershocks of the ML7.3 Haicheng earthquake (after Gu et al,1976) and their Euclidean distance DFM value

    序号发震时刻地理坐标ML深度
    /km
    节面Ⅰ节面ⅡPTB DFM
      年-月-日 时:分:秒东经/°北纬/°走向/°倾角/°滑动角/°走向/°倾角/°滑动角/°方位角/°俯角/°方位角/°俯角/°方位角/°俯角/°
    11975-02-0407:50:47.0122.7540.674.7171108525.1 1765174.5 6115 1572230064 18.85
    21975-02-0410:35:35.0122.7840.674.3151098622.1 1768175.7 6113 1551829768 15.66
    31975-02-0419:36:06.0122.8040.657.31229081−15.2 2375−170.7 6617.5157 410072.50
    41975-02-0501:01:45.0122.9340.704.410298884.020886178.02522 343 414386 17.67
    51975-02-0502:56:29.0122.8240.674.510112886.0 2284178.0 663 157 631083 14.64
    61975-02-0512:33:00.0122.7740.684.1101266111.522180150.526828 17113 5959 29.52
    71975-02-0523:52:54.0122.6340.704.610125645.621785153.926422 16814 4764 23.77
    81975-02-0605:43:42.0122.9040.625.22329287−2.0 2288−177.0 673 338 023186 15.11
    91975-02-0612:24:57.0122.5040.805.4171628034.625956167.929531 351614954 132.71
    101975-02-0613:56:16.0122.8340.754.01011680−128.9 1440−15.716941 562530438 147.66
    111975-02-0802:30:23.0122.4740.824.01216178−31.826259−166.029338 371814848 131.25
    121975-02-1220:42:46.0122.7840.704.0 714352−118.2 346−58.917168 73 334122 143.64
    131975-02-1521:08:02.0122.7840.705.4121118426.2 1864173.3 6214 1582230363 18.79
    141975-02-1622:01:26.0122.8040.685.311123626.8 3084151.826015 16324 2062 25.26
    151975-02-1818:51:49.0122.6540.774.2171144414.5 1480133.125223 14239 542 38.94
    161975-02-2215:45:14.0122.7340.704.0121138536.2 1954173.8 6021 1622930054 26.42
    171975-02-2405:07:20.0122.8840.784.4 713257−52.925848−132.927860 17 511030 149.77
    181975-02-2504:52:10.0122.6240.734.41413474−4.222686−164.027614 180 8 6274 159.93
    191975-02-2605:09:53.0122.8240.674.3 81219020.021070180.025414 3471412170 16.62
    201975-03-2111:32:59.0122.9540.774.01126072−29.6 062−159.5 3834 132 723156 41.11
    211975-03-2923:16:36.0122.6040.774.1 61118524.1 1966174.5 6313 1582030365 16.92
    221975-04-1003:55:37.0122.4840.724.610118859.0 2781184.92533 1631035780 18.20
    231975-04-2100:17:06.0122.4540.774.0 81098430.2 1660173.1 5917 1572529959 22.14
    241975-07-0407:06:29.0122.6740.724.11013756−19.423974−144.428336 18512 8052 157.73
    下载: 导出CSV

    表  2   岫岩MS5.4地震MS≥4.0前震和余震的震源机制解(引自张萍,蒋秀琴,2001)及其与主震之间的欧氏距离DFM

    Table  2   Focal mechanisms for MS≥4.0 foreshocks and aftershocks of the MS5.4 Xiuyan earthquake (after Zhang,Jiang,2001) and their Euclidean distance DFM value

    序号发震日期地理坐标MS深度
    /km
    节面Ⅰ节面ⅡP T B DFM
      年-月-日 时:分:秒东经/°北纬/°走向/°倾角/°滑动角/°走向/°倾角/°滑动角/°方位角/°俯角/°方位角/°俯角/°方位角/°俯角/°
    11999-11-0907:01:40.6123.0340.534.19320707.522883159.8261263581120870159.33
    21999-11-0907:07:21.2123.0240.534.2813780−7.122883−169.9 6218331 3 8477158.79
    31999-11-2520:47:48.5123.0040.554.081374429.5 2770130.0 5625150 8 113839.46
    41999-11-2520:55:4.2123.0040.554.491394230.7 2770127.72711216746 123642.50
    51999-11-2623:34:01.0123.0240.534.491107010.6 2480159.72461515212 466717.00
    61999-11-2912:10:39.2123.0340.535.4929684−20.1 2870−173.6 624119136280700
    71999-11-2912:45:50.4123.0340.535.1930070173.62068420.1 1240262221936811.36
    81999-11-2916:16:47.6123.0340.535.081118020.3 1770169.424820341 83246716.52
    91999-11-3007:52:55.8123.0340.534.091116813.0 1578157.526232162153486524.78
    101999-11-3013:58:17.7123.0340.535.2929180−16.3 2674−169.627015180 2260709.33
    111999-11-3014:06:55.1122.9840.554.982927210.519780161.7 4122133101667018.25
    121999-11-3014:09:36.6123.0240.554.391125811.8 1680147.4 7728350 33575720.22
    131999-11-3020:19:44.2123.0340.534.3929583−20.2 2870−172.529325 3725279704.69
    141999-12-0101:47:1.9123.0340.534.292908010.219880169.8 6722338 61547817.03
    151999-12-0104:33:0.5123.0340.534.491108030.5 1460168.4 428274 03076020.71
    161999-12-0112:45:30.8123.0340.554.392997010.620580159.729014 18 21176816.64
    171999-12-1305:49:30.5123.0840.534.111 1376023.3 3670147.9 7942346 2 85238.18
    181999-12-2719:27:15.4123.0240.534.081127010.6 1980159.7 9130 0 93566614.73
    192000-01-1207:43:55.4123.0540.535.5814680−40.725650−166.9 70253331313950140.51
    202000-01-1213:00:31.9123.0340.554.391128826.0 2064177.826913359 12976210.20
    下载: 导出CSV

    表  3   1999年岫岩MS5.4地震前小震震源机制

    Table  3   Focal mechanisms for small earthquakes before the MS5.4 Xiuyan earthquake in 1999

    序号发震日期地理坐标 MS深度
    /km
    节面Ⅰ节面ⅡPTB
      年-月-日 时:分:秒东经/°北纬/°走向/°倾向倾角/°走向/°倾向倾角/°方位角/°俯角/°方位角/°俯角/°方位角/°俯角/°
    11999-01-1503:05:18.6122.6240.65 3.411128WS80 42NW62261263581111059
    21999-01-0605:43:10.9122.8240.65 2.910105NE76 17ES80 6218331 323372
    31999-01-2007:37:43.4122.5340.70 3.212101NE80 13ES70 5625150 825965
    41999-04-0916:31:48.0121.0042.00 3.015138WS52 32ES702711216746 1243
    51999-04-2321:13:38.4122.8240.70 2.9 7107WS70 20NW862461515212 1368
    61999-04-2715:14:14.4124.5741.12 2.813125NE85 40ES30 62411913630430
    71999-04-3021:16:13.3122.8539.68 2.7 5142NE78 60NW42 12402622215239
    81999-05-1112:29:25.9122.7840.65 3.414114WS80 27NW7024820341 8 9068
    91999-05-1501:45:46.6122.2239.38 3.110118WS55 35NW802623216215 5052
    101999-05-2220:40:45.1122.4740.73 3.4 9133WS82 46NW8027015180 2 9378
    111999-05-2415:58:35.1122.2041.70 2.528 86NW80 0NE68 41221331024667
    121999-05-2903:13:30.9121.0042.00 3.321119NE70 34ES72 7728350 325364
    131999-06-0301:46:50.2122.2541.67 3.4 8 75NW64164NE9029325 372516464
    141999-06-0616:51:47.4122.8240.65 2.814110NE70 26ES80 6722338 623166
    151999-08-2112:56:25.9121.7041.25 2.721142NE70 45NW70 428274 018361
    161999-08-3115:11:21.0122.2339.35 2.914153WS80 64NW8029014 18 210875
    171999-09-0605:05:30.3122.6740.70 3.1 6114NE58 41ES64 7942346 225247
    181999-09-2013:22:57.0122.6740.68 2.9 5136NE62 52ES76 9130 0 925658
    191999-10-1007:21:15.5122.9540.65 2.8 9109NE59 24ES80 70253331321956
    201999-10-1216:04:20.3122.1840.48 3.414132WS80 46NW8026913359 1 8774
    211999-11-0414:46:26.9122.6039.27 3.5 7118WS57 14ES7015239252 534850
    221999-11-0903:34:1.3121.5738.52 3.9 9114NE62 22ES902703713937 2225
    231999-11-0908:21:36.2123.0040.53 2.9 8118NE70 32ES80 7720345 724067
    241999-11-0917:44:44.6123.0040.53 3.6 8121NE70 34ES80 8020347 823867
    251999-11-1618:57:48.5123.0040.53 3.0 9110NE90 20ES60 61211612129160
    261999-11-1703:09:31.4123.0040.53 2.7 9112WS70 24NW8224920156 9 4370
    271999-11-1723:59:50.8123.0040.55 2.5 9102WS80 14NW8423911148 4 4677
    281999-11-1808:15:41.2123.0040.53 2.8 9111NE80 29ES50 62371672028048
    291999-11-2100:50:1.9123.0040.55 3.0 8122NE72 40ES70 8128172 226564
    301999-11-2500:59:19.2123.0040.55 3.0 8112NE80 32ES42 60391722528340
    311999-11-2521:17:50.8123.0040.53 3.5 8138NE70 55ES70 9630187 127861
    321999-11-2522:08:12.4123.0040.53 3.2 8147WS76 61NW8028518194 2 9273
    331999-11-2523:19:17.5123.0040.55 3.2 8110WS80 24NW7024620338 6 8467
    341999-11-2603:18:23.3123.0040.55 2.7 9123NE72 39ES70 8027171 126361
    351999-11-2623:36:20.7123.0040.53 3.1 9112NE60 38ES60 7740344 325346
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    411999-11-2909:25:51.2123.0040.53 2.7 8126NE38 44ES86 99373462922660
    下载: 导出CSV
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  • 收稿日期:  2019-04-11
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