基于ETAS模型对三峡库区流体触发微震活动的定量检测
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摘要
针对ETAS模型参数估计方法(MLE)中的初值敏感性问题,提出GA+MLE算法,以GA结果作为MLE算法的初始输入,对结果进行精细计算.通过ETAS模型研究三峡库区微震活动在快速加载及缓慢卸载两种状态下的流体触发、地震自激发及微震活动衰减特征,讨论库水渗透及加卸载过程的可能影响.结果显示:(1)库水快速加载阶段ETAS模型参数μ、α、p及流体触发地震所占比例Rb均显示由小变大、又由大变小的变化过程,但p值的统计差异不显著;在库水缓慢卸载阶段,μ与Rb持续减小;(2)平均来看,库水快速加载阶段流体对微震活动显示较强的外因触发作用,同一条件下序列地震自激发明显增强、衰减相对较慢;水位缓慢卸载阶段,流体对地震活动的触发影响相对较弱,地震自激发不强、衰减相对较快;(3)分阶段来看,蓄水初期库水作用对微震活动的外因触发影响较弱,随库水位的升高及作用时间的增长,流体渗透逐渐发挥作用,孔隙压逐渐增大,流体外因触发作用明显增强,大多数微震活动缘于流体的直接触发(Rb≥95%);足够长的时间之后,由于地下数公里范围在新的载荷及渗透条件下趋于新的平衡,流体渗透影响趋于稳定,孔隙压趋于常数,孔隙压变化趋于0,流体对微震活动的触发作用逐渐减弱.
To solve the sensitivity problem of the initial value in the MLE algorithm for ETAS model parameter estimation,the GA+MLE method has been proposed in this paper.We take the results of GA(genetic algorithm) as the initial input of MLE,and then estimate the ETAS model parameters more accurately.Under two conditions of quick load and slow unload,the features of fluid triggering,self-generation of earthquakes and sequence decay in the Three Gorge Reservoir area has been studied by the ETAS model.The potential influence of fluid intrusion and load-unload process on seismicity has been discussed roughly.The results show that for quick load phase,the ETAS model parameters,μ,α and p,as well as the Rb,the ratio of fluid-induced earthquakes to total earthquakes,have a positive correlation,all of which showing a similar changing tendency: from small to large,and then to small.But the statistic difference of p value is not very obvious.For slow unload phase,μ and Rb values decrease unceasingly.Averagely,the fluid triggering on seismicity is something strong during the quick load phase.Meanwhile,the self-generation of earthquakes enhances obviously and decay tends to slow down.During the slow unload stage,the fluid triggering on microearthquake activity is relatively weak.In this situation the self-generation is weak and the decay is somewhat quick.For different phases,the influence of fluid triggering on seismicity is weak during the initial phase of water storage.With the time going and with the increase of water level,the pore pressure increases gradually due to the fluid intrusion,and the fluid triggering on seismicity increases obviously.Most of microearthquakes during this phase are caused by the direct fluid triggering(Rb≥95%).After the time long enough,the medium several kilometers below the reservoir becomes saturated under the new condition and the influence of fluid intrusion tends to be stable.In this case,the pore pressure approaches constant and the variation of pore pressure approaches zero,therefore the fluid triggering on microearthquakes decreases gradually.
To solve the sensitivity problem of the initial value in the MLE algorithm for ETAS model parameter estimation,the GA+MLE method has been proposed in this paper.We take the results of GA(genetic algorithm) as the initial input of MLE,and then estimate the ETAS model parameters more accurately.Under two conditions of quick load and slow unload,the features of fluid triggering,self-generation of earthquakes and sequence decay in the Three Gorge Reservoir area has been studied by the ETAS model.The potential influence of fluid intrusion and load-unload process on seismicity has been discussed roughly.The results show that for quick load phase,the ETAS model parameters,μ,α and p,as well as the Rb,the ratio of fluid-induced earthquakes to total earthquakes,have a positive correlation,all of which showing a similar changing tendency: from small to large,and then to small.But the statistic difference of p value is not very obvious.For slow unload phase,μ and Rb values decrease unceasingly.Averagely,the fluid triggering on seismicity is something strong during the quick load phase.Meanwhile,the self-generation of earthquakes enhances obviously and decay tends to slow down.During the slow unload stage,the fluid triggering on microearthquake activity is relatively weak.In this situation the self-generation is weak and the decay is somewhat quick.For different phases,the influence of fluid triggering on seismicity is weak during the initial phase of water storage.With the time going and with the increase of water level,the pore pressure increases gradually due to the fluid intrusion,and the fluid triggering on seismicity increases obviously.Most of microearthquakes during this phase are caused by the direct fluid triggering(Rb≥95%).After the time long enough,the medium several kilometers below the reservoir becomes saturated under the new condition and the influence of fluid intrusion tends to be stable.In this case,the pore pressure approaches constant and the variation of pore pressure approaches zero,therefore the fluid triggering on microearthquakes decreases gradually.
引文
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[2]El Hariri M,Abercrombie R E,Rowe C A,et al.The roleof fluids in triggering earthquakes:observations fromreservoir induced seismicity in Brazil.Geophys.J.Int.,2010,181:1566-1574.
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[6]Hainzl S,Ogata Y.Detecting fluid signals in seismicity datathrough statistical earthquake modeling.J.Geophys.Res.,2005,110:B05S07,doi:10.1029/2004JB003247.
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[11]蒋海昆,杨马陵,孙学军等.暴雨触发局部地震活动的一个典型例子:2010年6月广西凌云—凤山交界3级震群活动.地球物理学报,2011,54(10):2606-2619.Jiang H K,Yang M L,Sun X J,et al.A typical example oflocally triggered seismicity in the boundary area of Lingyunand Fengshan following the large rainfall event of June 2010.Chinese J.Geophys.(in Chinese),2007,54(10):1778-1786.
[12]Ogata Y.Increased probability of large earthquakes nearaftershock regions with relative quiescence.J.Geophys.Res.,2001,106(B5):8729-8744.
[13]蒋海昆,郑建常,吴琼等.传染型余震序列模型震后早期参数特征及其地震学意义.地球物理学报,2007,50(6):1778-1786.Jiang H K,Deng J C,Wu J,et al.Earlier statistical featuresof ETAS model parameters and their seismological meanings.Chinese J.Geophys.(in Chinese),2007,50(6):1778-1786.
[14]Clement Narteau,Svetlana Byrdina,Peter Shebalin,et al.Common dependence on stress for the two fundamental lawsof statistical seismology.Nature,2009,462(7273):642-646.
[15]易大义,蒋叔豪,李有法.数值方法.杭州:浙江科学技术出版社,1984:58-113.Yi D Y,Jiang S H,Li Y F.Numerical Method.Hangzhou:Zhejiang Science and Technology Press,1984:58-113
[16]杨晓源,张绿茵.三峡水库诱发地震监测简介.四川地震,2001,(2):1-5.Yang X Y,Zhang L Y.Introduction on monitoring system ofearthquakes induced by Sanxia Reservoir.EarthquakeResearch In Sichuan(in Chinese),2001,(2):1-5.
[17]谢蓉华,宋澄,邵玉坪.我国水库地震监测数字化进展.水电站设计,2008,24(2):79-82.Xie R H,Song C,Shao Y P.Progress of digital monitoringon induced earthquakes in Chinese mainland.Design ofPower Dam(in Chinese),2008,(24):79-82.
[18]廖武林,张丽芬,姚运生.三峡水库地震活动特征研究.地震地质,2009,31(4):707-714.Liao W L,Zhang L F,Yao Y S.Characteristics of seismicityin the three gorges reservoir area.Seismology and Geology(in Chinese),2009,31(4):707-714.
[19]车用太,陈俊华,张莉芬等.长江三峡工程库首区胡家坪MS4.1水库诱发地震研究.地震,2009,29(4):1-13.Che Y T,Chen J H,Zhang L F,et al.Study of the reservoirinduced Hujiaping MS4.1Earthquake in the three gorges damarea.Earthquake(in Chinese),2009,29(4):1-13.
[20]Utsu T,Ogata Y,Matsuura R S.The Centenary of theOmori formula for a decay law of aftershock activity.J.Phys.Earth.,1995,43(1):1-33.
[21]Xinglin L.Possible roles of the Zipingpu reservoir intriggering the 2008Wenchuan earthquake.Journal of AsianEarth Sciences,2011,40(4):844-854.
1)Ogata Y.Statistical Analysis of Seismicity-Updated Version(SASeis2006).2006:12-19
2)蒋海昆等.2010年7月,水库地震序列统计特征及与水库加卸载关系研究.国家“十一五”科技支撑计划项目子专题中期检查材料.
3)石耀霖.遗传算法及其在地球科学中的应用,中国科学院中国科学技术大学研究生院讲义.1994.
4)湖北省地震局,2008年11月22日秭归县屈原镇M s4.1地震宏观烈度调查报告,2008年12月
5)蒋海昆等.《水库地震序列统计特征与水库加卸载关系研究》,国家科技支撑计划项目专题(2008BAC38B03-01)研究报告第5章:水库诱发地震活动的定量检测及可能机理讨论.2011年8月.
6)蒋海昆等.2011年8月.《水库地震序列统计特征与水库加卸载关系研究》,国家科技支撑计划项目专题(2008BAC38B03-01)研究报告第5章:水库诱发地震活动的定量检测及可能机理讨论.
[2]El Hariri M,Abercrombie R E,Rowe C A,et al.The roleof fluids in triggering earthquakes:observations fromreservoir induced seismicity in Brazil.Geophys.J.Int.,2010,181:1566-1574.
[3]于品清,周明礼,杨淑贤.未来三峡水库区诱发岩溶型水库地震的可能震级.华南地震,1992,12(2):81-87.Yu P Q,Zhou M L,Yang S X.Possible magnitude ofinduced Karst earthquake in the reservoir which will be builtin the coming years.South China Journal of Seismology(inChinese),1992,12(2):81-87.
[4]高士钧,王青云,宋慧珍等.长江三峡地区地壳应力场与地震.北京:地震出版社,1992:4-9.Gao S J,Wang Q Y,Song H Z,et al.Crustal Stress Fieldand Earthquakes in Changjiang Sanxia Region.Beijing:Earthquake Press,1992:4-9
[5]于品清.从水文地质条件探讨未来三峡水库发生构造型水库地震的可能性.华南地震,1993,13(1):76-83.Yu P Q.Discussion on the possible tectonic earthquake inChangjiang three-gorge reservoir area in relation tohydrogeologic conditions.South China Journal ofSeismology(in Chinese),1993,13(1):76-83.
[6]Hainzl S,Ogata Y.Detecting fluid signals in seismicity datathrough statistical earthquake modeling.J.Geophys.Res.,2005,110:B05S07,doi:10.1029/2004JB003247.
[7]Ogata Y.Statistical models for earthquake occurrences andresidual analysis for point processes.J.Am.Stat.Assoc.,1988,83(401):9-27.
[8]Ogata Y.Statistical model for standard seismicity anddetection of anomalies by residual analysis.Tectonophysics,1989,169(1-3):159-174.
[9]Ogata Y.Space-time point-process models for earthquakeoccurrences.Ann.Inst.Stat.Math.,1998,50(2):379-402.
[10]Lei X L,Yu G Z,Ma S L,et al.Earthquakes induced bywater injection at-3km depth within the Rongchang gas field,Chongqing.China.J Geophys.Res.,2008,113:B10310,doi:10.1029/2008JB005604.
[11]蒋海昆,杨马陵,孙学军等.暴雨触发局部地震活动的一个典型例子:2010年6月广西凌云—凤山交界3级震群活动.地球物理学报,2011,54(10):2606-2619.Jiang H K,Yang M L,Sun X J,et al.A typical example oflocally triggered seismicity in the boundary area of Lingyunand Fengshan following the large rainfall event of June 2010.Chinese J.Geophys.(in Chinese),2007,54(10):1778-1786.
[12]Ogata Y.Increased probability of large earthquakes nearaftershock regions with relative quiescence.J.Geophys.Res.,2001,106(B5):8729-8744.
[13]蒋海昆,郑建常,吴琼等.传染型余震序列模型震后早期参数特征及其地震学意义.地球物理学报,2007,50(6):1778-1786.Jiang H K,Deng J C,Wu J,et al.Earlier statistical featuresof ETAS model parameters and their seismological meanings.Chinese J.Geophys.(in Chinese),2007,50(6):1778-1786.
[14]Clement Narteau,Svetlana Byrdina,Peter Shebalin,et al.Common dependence on stress for the two fundamental lawsof statistical seismology.Nature,2009,462(7273):642-646.
[15]易大义,蒋叔豪,李有法.数值方法.杭州:浙江科学技术出版社,1984:58-113.Yi D Y,Jiang S H,Li Y F.Numerical Method.Hangzhou:Zhejiang Science and Technology Press,1984:58-113
[16]杨晓源,张绿茵.三峡水库诱发地震监测简介.四川地震,2001,(2):1-5.Yang X Y,Zhang L Y.Introduction on monitoring system ofearthquakes induced by Sanxia Reservoir.EarthquakeResearch In Sichuan(in Chinese),2001,(2):1-5.
[17]谢蓉华,宋澄,邵玉坪.我国水库地震监测数字化进展.水电站设计,2008,24(2):79-82.Xie R H,Song C,Shao Y P.Progress of digital monitoringon induced earthquakes in Chinese mainland.Design ofPower Dam(in Chinese),2008,(24):79-82.
[18]廖武林,张丽芬,姚运生.三峡水库地震活动特征研究.地震地质,2009,31(4):707-714.Liao W L,Zhang L F,Yao Y S.Characteristics of seismicityin the three gorges reservoir area.Seismology and Geology(in Chinese),2009,31(4):707-714.
[19]车用太,陈俊华,张莉芬等.长江三峡工程库首区胡家坪MS4.1水库诱发地震研究.地震,2009,29(4):1-13.Che Y T,Chen J H,Zhang L F,et al.Study of the reservoirinduced Hujiaping MS4.1Earthquake in the three gorges damarea.Earthquake(in Chinese),2009,29(4):1-13.
[20]Utsu T,Ogata Y,Matsuura R S.The Centenary of theOmori formula for a decay law of aftershock activity.J.Phys.Earth.,1995,43(1):1-33.
[21]Xinglin L.Possible roles of the Zipingpu reservoir intriggering the 2008Wenchuan earthquake.Journal of AsianEarth Sciences,2011,40(4):844-854.
1)Ogata Y.Statistical Analysis of Seismicity-Updated Version(SASeis2006).2006:12-19
2)蒋海昆等.2010年7月,水库地震序列统计特征及与水库加卸载关系研究.国家“十一五”科技支撑计划项目子专题中期检查材料.
3)石耀霖.遗传算法及其在地球科学中的应用,中国科学院中国科学技术大学研究生院讲义.1994.
4)湖北省地震局,2008年11月22日秭归县屈原镇M s4.1地震宏观烈度调查报告,2008年12月
5)蒋海昆等.《水库地震序列统计特征与水库加卸载关系研究》,国家科技支撑计划项目专题(2008BAC38B03-01)研究报告第5章:水库诱发地震活动的定量检测及可能机理讨论.2011年8月.
6)蒋海昆等.2011年8月.《水库地震序列统计特征与水库加卸载关系研究》,国家科技支撑计划项目专题(2008BAC38B03-01)研究报告第5章:水库诱发地震活动的定量检测及可能机理讨论.
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