甘东南流动台阵微震监测结果
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摘要
利用高密度宽频带流动台阵资料,应用网格搜索地震定位方法对甘东南2009年11月—2011年11月期间的微震进行了重新定位。在研究区内有3个以上台站记录到的微震共3 014个,比常规台网记录多1 693个。重新定位结果显示:在各断裂带附近地震分布更加密集,沿断裂呈带状或簇集状分布;震源深度分布优势范围为5～20km,其平均深度为11km;地震深度分布与断裂的关系密切,地震条带与断裂构造可以较好的相对应。
In November 2009,a high-density portable seismic array consisting of 150 broadband seismographs was deployed in southeast Gansu province through the cooperation of the Lanzhou Institute of Seismology and the Institute of Geology,CEA.We obtained a large amount of microearthquakes data recorded by this array through November 2011.The data of the portable seismic array and the permanent seismic network is merged and saved in Windows Event Log(EVT) format.On the basis of the amplitude frequency characteristics of seismic waves,we design an automatic identification program of earthquake events,adjust the threshold,and clip the waveforms.We then use EDIAS/MSDP software to re-identify earthquake events,analyze seismic phases,and locate earthquakes by using the simplex location method.The initial localization of 3 243 earthquakes events in the region(32.9°-35.0° N,102.7°-107.1° E) is obtained.Finally,we relocate these earthquakes by using the grid searching algorithm.In this algorithm,the 3-D velocity model is used to obtain theoretical travel times by the ray tracing method.By computing the root mean square(RMS) residuals of theoretical and observational travel times,the corresponding point of the minimum residual is determined as the relocation point.Accurate relocation of 3014 microearthquakes recorded by three or more stations is obtained with this algorithm,which is 1 693 more than that obtained from the permanent seismic network in the same period.We apply the results to seismicity analysis in southeast Gansu province and discuss the relationship between seismicity and active faults.The seismic data recorded on three profiles across several fault zones and the spatial distribution of the faults is analyzed in detail.The results show that the relocated earthquakes are more concentrated on obvious strips or clustered around the faults.Most of these faults have comparatively strong seismicity in southeast Gansu,particularly those concentrated in the Wenxian-Wudu area,which is the transform zone of several groups of faults.However,seismic activity of the Tianshui eastern segment of the West Qinling Northern Frontal fault is relatively weak.The focal depths of the earthquake swarm are mainly distributed in the range of 5~20 km,which proves that the seismogenic layer is in the upper or middle crust in this area at an average of 11 km.As indicated by the focal depth profile,the focal depths are closely related to the faults,and earthquake belts correspond well with faulted structures.The fault zone is composed of the Diebu-Bailongjiang and Guanggaishan-Dieshan southern and northern Piedmont faults within a width of 20 km.The Tazang fault belt and the Lintan-Tanchang fault zone are wider.In depth direction,the earthquakes are obviously compact on strips near the West Qinling Northern Frontal fault,the Wenxian-Kanxian fault zone,and the Chengxian basin Northern and Southern Frontal fault.The seismic activities of these faults extend to the middle crust and upper part of the lower crust.
In November 2009,a high-density portable seismic array consisting of 150 broadband seismographs was deployed in southeast Gansu province through the cooperation of the Lanzhou Institute of Seismology and the Institute of Geology,CEA.We obtained a large amount of microearthquakes data recorded by this array through November 2011.The data of the portable seismic array and the permanent seismic network is merged and saved in Windows Event Log(EVT) format.On the basis of the amplitude frequency characteristics of seismic waves,we design an automatic identification program of earthquake events,adjust the threshold,and clip the waveforms.We then use EDIAS/MSDP software to re-identify earthquake events,analyze seismic phases,and locate earthquakes by using the simplex location method.The initial localization of 3 243 earthquakes events in the region(32.9°-35.0° N,102.7°-107.1° E) is obtained.Finally,we relocate these earthquakes by using the grid searching algorithm.In this algorithm,the 3-D velocity model is used to obtain theoretical travel times by the ray tracing method.By computing the root mean square(RMS) residuals of theoretical and observational travel times,the corresponding point of the minimum residual is determined as the relocation point.Accurate relocation of 3014 microearthquakes recorded by three or more stations is obtained with this algorithm,which is 1 693 more than that obtained from the permanent seismic network in the same period.We apply the results to seismicity analysis in southeast Gansu province and discuss the relationship between seismicity and active faults.The seismic data recorded on three profiles across several fault zones and the spatial distribution of the faults is analyzed in detail.The results show that the relocated earthquakes are more concentrated on obvious strips or clustered around the faults.Most of these faults have comparatively strong seismicity in southeast Gansu,particularly those concentrated in the Wenxian-Wudu area,which is the transform zone of several groups of faults.However,seismic activity of the Tianshui eastern segment of the West Qinling Northern Frontal fault is relatively weak.The focal depths of the earthquake swarm are mainly distributed in the range of 5~20 km,which proves that the seismogenic layer is in the upper or middle crust in this area at an average of 11 km.As indicated by the focal depth profile,the focal depths are closely related to the faults,and earthquake belts correspond well with faulted structures.The fault zone is composed of the Diebu-Bailongjiang and Guanggaishan-Dieshan southern and northern Piedmont faults within a width of 20 km.The Tazang fault belt and the Lintan-Tanchang fault zone are wider.In depth direction,the earthquakes are obviously compact on strips near the West Qinling Northern Frontal fault,the Wenxian-Kanxian fault zone,and the Chengxian basin Northern and Southern Frontal fault.The seismic activities of these faults extend to the middle crust and upper part of the lower crust.
引文
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[7]李松林,张先康,张成科,等.玛沁—兰州—靖边地震测深剖面地壳速度结构的初步研究[J].地球物理学报,2002,45(2):210-217.Li S L,Zhang X K,Zhang C K,et al.A Preliminary Study on the Crustal Velocity Structure of Maqin-Lanzhou-Jingbian byMeans of Deep Seismic Sounding Profile[J].Chinese J.Geo-phys.,2002,45(2):210-217.
[8]周民都,张元生,石雅缪,等.青藏高原东北缘地壳三维速度结构[J].地球物理学进展,2006,21(1):127-134.Zhou M D,Zhang Y S,Shi Y L,et al.Three-dimensional Crus-tal Velocity Structure in the Northeastern Margin of the Qinghai-Tibetan Plateau[J].Progress in Geophysics,2006,21(1):127-134.
[9]高尔根,徐果明.二维速度随机分布逐步迭代射线追踪方法[J].地球物理学报,1996,39(增刊):302-308.Gao E G,Xu G M.A New Kind of Step by Step Iterative Ray-Tracing Method[J].Chinese J.Geophys.,1996,39(Supp.):302-308.
[10]张元生,周民都,荣代潞,等.祁连山中东段地区三维速度结构研究[J].地震学报,2004,26(3):247-255.Zhang Y S,Zhou M D,Rong D L,et al.3-D Velocity Struc-ture in the Central-Eastern Part of Qilian Shan[J].Acta Seis-mologica Sinica,2004,26(3):247-255.
[11]邓启东,冉永康,杨晓平,等.中国活动构造图[M].北京:地震出版社,2007.Deng Q D,Ran Y K,Yang X P,et al.Map of Active Tecton-ics in China[M].Beijing:Seismological Press,2007.
[12]Yang ZX,Chen YT,Zheng YJ,Yu XW,Accurate Relocation of Earthquakes in Central-western China using the Double-difference Earthquake Location Algorithm[J].Science in Chi-na,2003,46:181-188.
[13]周真恒,邓万明.壳内多震层孕震环境研究进展[J].地震地质,1998,20(4):443-453.Zhou Z H,Deng W M,Xiang C Y.Advances of Research on the Intracrustal Seismogenic Layer[J].Seismology and Geolo-gy,1998,20(4):443-453.
[14]莘海亮,刘明军,张元生,等.甘东南地区地震重新定位研究[J].地震学报,2010,33(3):292-299.Xin H L,Liu M J,Zhang Y S,et al.Relocation of the Earth-quakes in the Southeast Area of Gansu[J].Journal of Seismo-logical Research,2010,33(3):292-299.
[2]惠少兴,张元生,李顺成.t-D地震定位方法研究[J].西北地震学报,2012,34(1):10-13.Hui S X,Zhang Y S,Li S C.Study on the t-D Earthquake Loca-tion Method[J].Northwestern Seismological Journal,2012,34(1):10-13.
[3]张少泉,武利均,郭蔑明.中国西部地区门源—平凉—渭南地震测深剖面资料的分析解释[J].地球物理学报,1985,28(5):460-472.Zhang S Q,Wu L J,Juo J M.An Interpretation of the Dss Dataon Menyuan-Pingling-Weinan Profile in West China[J].Chi-nese J.Geophys,1985,28(5):460-472.
[4]李清和,闵祥仪,郭建康,等.天水—礼县地区地壳速度结构[J].西北地震学报,1990,12(2):49-58.Li Q H,Min X Y,Guo J K,et al.The Crustal Velocity Struc-ture in Tianshui-Lixian Region[J].Northwestern Seismologi-cal Journal,1990,12(2):49-58.
[5]闵祥仪,周民都,郭建康,等.灵台—阿木去乎剖面地壳速度结构[J].西北地震学报,1991,13(增刊):29-36.Min X Y,Zhou M D,Guo J K,et al.The Crustal Velocity Structure in Lingtai-Amuquhu Profile[J].Northwestern Seis-mological Journal,1991,13(Supp.):29-36.
[6]李清河,郭建康,周民都,等.成县—西吉剖面地壳速度结构[J].西北地震学报,1991,13(增刊):37-43.Li Q H,Guo J K,Zhou M D,et al.The Velocity Structure of Chengxian-Xiji Profile[J].Northwestern Seismological Jour-nal,1991,13(Supp.):37-43.
[7]李松林,张先康,张成科,等.玛沁—兰州—靖边地震测深剖面地壳速度结构的初步研究[J].地球物理学报,2002,45(2):210-217.Li S L,Zhang X K,Zhang C K,et al.A Preliminary Study on the Crustal Velocity Structure of Maqin-Lanzhou-Jingbian byMeans of Deep Seismic Sounding Profile[J].Chinese J.Geo-phys.,2002,45(2):210-217.
[8]周民都,张元生,石雅缪,等.青藏高原东北缘地壳三维速度结构[J].地球物理学进展,2006,21(1):127-134.Zhou M D,Zhang Y S,Shi Y L,et al.Three-dimensional Crus-tal Velocity Structure in the Northeastern Margin of the Qinghai-Tibetan Plateau[J].Progress in Geophysics,2006,21(1):127-134.
[9]高尔根,徐果明.二维速度随机分布逐步迭代射线追踪方法[J].地球物理学报,1996,39(增刊):302-308.Gao E G,Xu G M.A New Kind of Step by Step Iterative Ray-Tracing Method[J].Chinese J.Geophys.,1996,39(Supp.):302-308.
[10]张元生,周民都,荣代潞,等.祁连山中东段地区三维速度结构研究[J].地震学报,2004,26(3):247-255.Zhang Y S,Zhou M D,Rong D L,et al.3-D Velocity Struc-ture in the Central-Eastern Part of Qilian Shan[J].Acta Seis-mologica Sinica,2004,26(3):247-255.
[11]邓启东,冉永康,杨晓平,等.中国活动构造图[M].北京:地震出版社,2007.Deng Q D,Ran Y K,Yang X P,et al.Map of Active Tecton-ics in China[M].Beijing:Seismological Press,2007.
[12]Yang ZX,Chen YT,Zheng YJ,Yu XW,Accurate Relocation of Earthquakes in Central-western China using the Double-difference Earthquake Location Algorithm[J].Science in Chi-na,2003,46:181-188.
[13]周真恒,邓万明.壳内多震层孕震环境研究进展[J].地震地质,1998,20(4):443-453.Zhou Z H,Deng W M,Xiang C Y.Advances of Research on the Intracrustal Seismogenic Layer[J].Seismology and Geolo-gy,1998,20(4):443-453.
[14]莘海亮,刘明军,张元生,等.甘东南地区地震重新定位研究[J].地震学报,2010,33(3):292-299.Xin H L,Liu M J,Zhang Y S,et al.Relocation of the Earth-quakes in the Southeast Area of Gansu[J].Journal of Seismo-logical Research,2010,33(3):292-299.
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