首都圈数字地震台网对微弱爆破信号的检测能力
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摘要
利用首都圈数字地震台网接收人工地震信号,进行地下结构研究具有重要意义.但人工震源释放的能量小,激发的地震波以短周期为主,因此本文较全面地研究了地震台网对短周期微弱信号(1～20 Hz)的检测能力:(1)分析了台网的背景噪声,结果表明基岩台址的地震台噪声比沉积盖层台址的地震台噪声低约13 dB,这相当于近1个震级的检测阈值;夜间的噪声比白天低约5 dB;噪声有逐年增高的趋势,2006年比2001年噪声提高约4 dB.(2)分析了在台网内进行的药量为25 kg的陆地井下爆破实验,一次爆破相当于0.69级(M_L)的天然地震,有18个地震台可辨认爆炸产生的 Pg、Pm 或 Pc 波;离爆破点218 km 的基岩台,仍可以接收到振幅只有1.6 nm 的 Pm 波.这个结果可为地震勘探实际工作提供参考.(3)研究了台网外核爆试验的信号特征,2006年发生在朝鲜的地下核试验是一次检验台网检测微弱信号能力的好机会.波形记录经1～5Hz 滤波后,台网中噪声小的18个基岩台可以清晰辨认核爆破产生的 P 波或 Lg 波,P 波平均振幅为16 nm,计算的平均震级为 m_b 4.3,和 NEIC 给出的震级相同;分析还表明背景噪声是影响台站信号检测能力的主要因素之一.
It is meaningful to use the Beijing metropolitan digital Seismic Network (BSN) of China to study deep crustal structure by recording artificial earthquakes.However,the energy released by artificial sources is small and they generally generate short-period seismic signals.In order to study the weak signal detectability of the Seismic Network between 1 and 20 Hz,this paper carries out the following work:(1) The analysis of background noise of BSN shows that the noise level at seismic stations on bedrock is about 13 dB lower than that at stations located on sedimentary layer.The difference of noise level is equivalent to variations of detectable earthquake magnitude 1.0.The noise between night and day time varies by about 5 dB.There is a trend of noise level increasing year-by-year.The noise level in 2006 is 4 dB higher than that in 2001.(2) A borehole explosion experiment with 25 kg chemical charges was conducted with its energy equal to an M_L 0.69 natural earthquake.The seismic phases Pg,Pm and Pc generated by explosion can be identified at 18 seismic stations.At a permanent seismic station 218 km away, the seismic phase Pm can be detected with the peak-to-peak amplitude being about 1.6 nanometers.(3) An underground nuclear explosion carried out by North Korea in 2006 is a good opportunity to examine the weak signal detectability of the BSN.The records filtered with 1～5 Hz shows that the P or Lg waves generated by the nuclear explosion can clearly be recorded by 18 seismic stations located on bedrock.The average amplitude of P waves is 16 nanometers.The magnitude calculated is m_b 4.3,the same as that given by NEIC.The result also shows the noise level of station is one of the most important factors for signal detectability.
It is meaningful to use the Beijing metropolitan digital Seismic Network (BSN) of China to study deep crustal structure by recording artificial earthquakes.However,the energy released by artificial sources is small and they generally generate short-period seismic signals.In order to study the weak signal detectability of the Seismic Network between 1 and 20 Hz,this paper carries out the following work:(1) The analysis of background noise of BSN shows that the noise level at seismic stations on bedrock is about 13 dB lower than that at stations located on sedimentary layer.The difference of noise level is equivalent to variations of detectable earthquake magnitude 1.0.The noise between night and day time varies by about 5 dB.There is a trend of noise level increasing year-by-year.The noise level in 2006 is 4 dB higher than that in 2001.(2) A borehole explosion experiment with 25 kg chemical charges was conducted with its energy equal to an M_L 0.69 natural earthquake.The seismic phases Pg,Pm and Pc generated by explosion can be identified at 18 seismic stations.At a permanent seismic station 218 km away, the seismic phase Pm can be detected with the peak-to-peak amplitude being about 1.6 nanometers.(3) An underground nuclear explosion carried out by North Korea in 2006 is a good opportunity to examine the weak signal detectability of the BSN.The records filtered with 1～5 Hz shows that the P or Lg waves generated by the nuclear explosion can clearly be recorded by 18 seismic stations located on bedrock.The average amplitude of P waves is 16 nanometers.The magnitude calculated is m_b 4.3,the same as that given by NEIC.The result also shows the noise level of station is one of the most important factors for signal detectability.
引文
1) 中国地震局分析预报中心.首都圈台网技术报告.首都圈防震减灾示范区系统工程项目单项工程验收材料(编号SSD-0-1) ,2002
[1] 陈顒,周华伟.葛洪魁.华北地震台阵探测计划.大地测量与地球动力学.2006． 25(4) :1～5 Chen Y,Zhou H W,Ge H K.Seismic Array in North China.Journal of Geodesy and Geodynamics(in Chinese),2006． 25(4) :1～5
[2] 刘瑞丰,吴忠良.阴朝民等.中国地震台网数字化改造的进展.地震学报.2003,25(5) :535～540 Liu R F,Wu Z L,Yin C M.et al.Development of China digital seismological observational systems.Acta Seismologica Sinica.2003． 16(5) :568～573
[3] 郭飙.刘启元.陈九辉等.首都圈数字地震台网的微震定位实验.地震地质.2002． 24(3) :453～459 Guo B.Liu Q Y.Chen J H.et al.Test of epicenter determination of microearthquakes by the digital seismic network in capital circle.Seismology and Geology(in Chinese),2002． 24(3) :453～459
[4] 黄金莉,赵大鹏.首都圈地区地壳三维P波速度细结构与强震孕育的深部构造环境.科学通报,2005,50(4) :348～355 Huang J L,Zhao D P.Fine three-dimensional P-wave velocity structure beneath the capital region and deep environment for the nucleation of strong earthquakes.Chinese Science Bulletin.2005． 50(6) :544～552
[5] 齐诚.赵大鹏.陈顒等.首都圈地区地壳P波和S波三维速度结构及其与大地震的关系.地球物理学报.2006,49(3) :805～815 Qi C.Zhao D P.Chen Y.et al.3-D P and S wave velocity structures and their relationship to strong earthquakes in the Chinese capital region.Chinese J.Geophys.(in Chinese),2006． 49(3) :805～815
[6] 赖院根.刘启元,陈九辉等.首都圈地区横波分裂与地壳应力场特征.地球物理学报.2006,49(1) :189～196 Lai Y G,Liu Q Y.Chen J H.et al.Shear wave splitting and the features of the crustal stress field in the Capital Circle. Chinese J.Geophys.(in Chinese),2006． 49(1) :189～196
[7] 吴晶,高原,陈运泰等.首都圈西北部地区地壳介质地震各向异性特征初步研究.地球物理学报.2007,50(1) :209～220 Wu J,Gao Y,Chen Y T.et al.Seismic anisotropy in the crust in northwestern capital area of China.Chinese J.Geophys.(in Chinese),2007． 50(1) :209～220
[8] 陈顒.张先康,丘学林等.陆地人工激发地震波的一种新方法.科学通报.2007,52(11) :1317～1321 Chen Y.Zhang X K,Qiu X L,et al.A new way to generate seismic waves for continental crustal exploration.Chinese Science Bulletin,2007,52(16) :2264～2268
[9] 林建民,王宝善,葛洪魁等.大容量气枪震源特征及深部介质中传播的震相分析.地球物理学报,2008,51(1) :206～212 Lin J M,Wang B S,Ge H K,et al.Study on large volume airgun source characteristics and seismic phase analysis.Chinese J.Geophys.(in Chinese),2008,51(1) :206～212
[10] 陈顒,朱日祥.设立“地下明灯研究计划”的建议.地球科学进展,2005,20(5) :485～489 Chen Y,Zhu R X.Proposed project of“Underground Bright Lump”.Advances in Earth Science(in Chinese),2005,20(5) :485～489
[11] 陈顒,王宝善,葛洪魁等.建立地震发射台的建议.地球科学进展,2007,22(5) :441～446 Chen Y,Wang B S.Ge H K,et al.Proposed of transmitted seismic stations.Advances in Earth Science(in Chinese),2007,22(5) :441～446
[12] 陈顒.张尉.陈汉林等.地震雷达.地球物理学进展,2006,21(1) :1～5 Chen Y,Zhang W,Chen H L,et al.Seismic Radar.Progress in Geophysics(in Chinese),2006,21(1) :1～5
[13] Peterson J.Observations and modeling of seismic background noise.U.S.Geol.Survey Open-File Report,1993． 93～322
[14] Webb S C.Seismic Noise on Land and on the Sea Floor.In:Lee W H K ed.International Handbook of Earthquake and Engineering Seismology.San Diego:Academic Press,2002． 305～318
[15] 嘉世旭,刘昌铨.华北地区人工地震测深震相与地壳结构研究.地震地质,1995． 17(2) :97～105 Jia S X,Liu C Q.Study on the seismic phase of DSS in North China.Seismology and Geology(in Chinese),1995,17(2) :97～105
[16] 李松林,张先康,宋占隆等.多条人工地震测深剖面资料联合反演首都圈三维地壳结构.地球物理学报,2001,44(3) :360～370 Li S L.Zhang X K.Song Z L.et al.Three-dimensional crustal structure of the capital area obtained by a joint inversion of DSS data from multiple profiles.Chinese J.Geophys.(in Chinese),2001,44(3) :360～370
[17] 嘉世旭,张先康.华北不同构造块体地壳结构及其对比研究.地球物理学报,2005,48(3) :611～620 Jia S X,Zhang X K.Crustal structure and comparison of different tectonic blocks in North China. Chinese J.Geophys.(in Chinese),2005,48(3) :611～620
[18] Ammon C J,Lay T.Nuclear Test Illuminates USArray Data Quality.EOS,2007,88(4) :37～38
[19] 彼得·鲍曼主编.新地震观测实践手册.中国地震局监测预报司译.北京:地震出版社,2006 Bormann P.New Manual of Seismological Observatory Practice. Department of Earthquake Monitoring and Prediction of China Earthquake Administration translated.Beijing:Seismological Press.2006
[20] Veith K F,Clawson G E.Magnitude from short-period P-wave data.Bull.Seismol.Soc.Am.,1972,62(2) :435～452
[21] Richards P G.Seismological methods of monitoring compliance with the Comprehensive Nuclear Test Ban Treaty.In:Lee W H K ed.International Handbook of Earthquake and Engineering Seismology.San Diego:Academic Press,2002． 369～382
[22] 罗桂纯,王宝善,葛洪魁等.气枪震源在地球深部结构探测中的应用研究进展.地球物理学进展,2006,21(2) :400～407 Luo G C,Wang B S,Ge H K,et al.Progress in Earth’s deep structures exploration by airgun source.Progress in Geophysics(in Chinese),2006,21(2) :400～407
[1] 陈顒,周华伟.葛洪魁.华北地震台阵探测计划.大地测量与地球动力学.2006． 25(4) :1～5 Chen Y,Zhou H W,Ge H K.Seismic Array in North China.Journal of Geodesy and Geodynamics(in Chinese),2006． 25(4) :1～5
[2] 刘瑞丰,吴忠良.阴朝民等.中国地震台网数字化改造的进展.地震学报.2003,25(5) :535～540 Liu R F,Wu Z L,Yin C M.et al.Development of China digital seismological observational systems.Acta Seismologica Sinica.2003． 16(5) :568～573
[3] 郭飙.刘启元.陈九辉等.首都圈数字地震台网的微震定位实验.地震地质.2002． 24(3) :453～459 Guo B.Liu Q Y.Chen J H.et al.Test of epicenter determination of microearthquakes by the digital seismic network in capital circle.Seismology and Geology(in Chinese),2002． 24(3) :453～459
[4] 黄金莉,赵大鹏.首都圈地区地壳三维P波速度细结构与强震孕育的深部构造环境.科学通报,2005,50(4) :348～355 Huang J L,Zhao D P.Fine three-dimensional P-wave velocity structure beneath the capital region and deep environment for the nucleation of strong earthquakes.Chinese Science Bulletin.2005． 50(6) :544～552
[5] 齐诚.赵大鹏.陈顒等.首都圈地区地壳P波和S波三维速度结构及其与大地震的关系.地球物理学报.2006,49(3) :805～815 Qi C.Zhao D P.Chen Y.et al.3-D P and S wave velocity structures and their relationship to strong earthquakes in the Chinese capital region.Chinese J.Geophys.(in Chinese),2006． 49(3) :805～815
[6] 赖院根.刘启元,陈九辉等.首都圈地区横波分裂与地壳应力场特征.地球物理学报.2006,49(1) :189～196 Lai Y G,Liu Q Y.Chen J H.et al.Shear wave splitting and the features of the crustal stress field in the Capital Circle. Chinese J.Geophys.(in Chinese),2006． 49(1) :189～196
[7] 吴晶,高原,陈运泰等.首都圈西北部地区地壳介质地震各向异性特征初步研究.地球物理学报.2007,50(1) :209～220 Wu J,Gao Y,Chen Y T.et al.Seismic anisotropy in the crust in northwestern capital area of China.Chinese J.Geophys.(in Chinese),2007． 50(1) :209～220
[8] 陈顒.张先康,丘学林等.陆地人工激发地震波的一种新方法.科学通报.2007,52(11) :1317～1321 Chen Y.Zhang X K,Qiu X L,et al.A new way to generate seismic waves for continental crustal exploration.Chinese Science Bulletin,2007,52(16) :2264～2268
[9] 林建民,王宝善,葛洪魁等.大容量气枪震源特征及深部介质中传播的震相分析.地球物理学报,2008,51(1) :206～212 Lin J M,Wang B S,Ge H K,et al.Study on large volume airgun source characteristics and seismic phase analysis.Chinese J.Geophys.(in Chinese),2008,51(1) :206～212
[10] 陈顒,朱日祥.设立“地下明灯研究计划”的建议.地球科学进展,2005,20(5) :485～489 Chen Y,Zhu R X.Proposed project of“Underground Bright Lump”.Advances in Earth Science(in Chinese),2005,20(5) :485～489
[11] 陈顒,王宝善,葛洪魁等.建立地震发射台的建议.地球科学进展,2007,22(5) :441～446 Chen Y,Wang B S.Ge H K,et al.Proposed of transmitted seismic stations.Advances in Earth Science(in Chinese),2007,22(5) :441～446
[12] 陈顒.张尉.陈汉林等.地震雷达.地球物理学进展,2006,21(1) :1～5 Chen Y,Zhang W,Chen H L,et al.Seismic Radar.Progress in Geophysics(in Chinese),2006,21(1) :1～5
[13] Peterson J.Observations and modeling of seismic background noise.U.S.Geol.Survey Open-File Report,1993． 93～322
[14] Webb S C.Seismic Noise on Land and on the Sea Floor.In:Lee W H K ed.International Handbook of Earthquake and Engineering Seismology.San Diego:Academic Press,2002． 305～318
[15] 嘉世旭,刘昌铨.华北地区人工地震测深震相与地壳结构研究.地震地质,1995． 17(2) :97～105 Jia S X,Liu C Q.Study on the seismic phase of DSS in North China.Seismology and Geology(in Chinese),1995,17(2) :97～105
[16] 李松林,张先康,宋占隆等.多条人工地震测深剖面资料联合反演首都圈三维地壳结构.地球物理学报,2001,44(3) :360～370 Li S L.Zhang X K.Song Z L.et al.Three-dimensional crustal structure of the capital area obtained by a joint inversion of DSS data from multiple profiles.Chinese J.Geophys.(in Chinese),2001,44(3) :360～370
[17] 嘉世旭,张先康.华北不同构造块体地壳结构及其对比研究.地球物理学报,2005,48(3) :611～620 Jia S X,Zhang X K.Crustal structure and comparison of different tectonic blocks in North China. Chinese J.Geophys.(in Chinese),2005,48(3) :611～620
[18] Ammon C J,Lay T.Nuclear Test Illuminates USArray Data Quality.EOS,2007,88(4) :37～38
[19] 彼得·鲍曼主编.新地震观测实践手册.中国地震局监测预报司译.北京:地震出版社,2006 Bormann P.New Manual of Seismological Observatory Practice. Department of Earthquake Monitoring and Prediction of China Earthquake Administration translated.Beijing:Seismological Press.2006
[20] Veith K F,Clawson G E.Magnitude from short-period P-wave data.Bull.Seismol.Soc.Am.,1972,62(2) :435～452
[21] Richards P G.Seismological methods of monitoring compliance with the Comprehensive Nuclear Test Ban Treaty.In:Lee W H K ed.International Handbook of Earthquake and Engineering Seismology.San Diego:Academic Press,2002． 369～382
[22] 罗桂纯,王宝善,葛洪魁等.气枪震源在地球深部结构探测中的应用研究进展.地球物理学进展,2006,21(2) :400～407 Luo G C,Wang B S,Ge H K,et al.Progress in Earth’s deep structures exploration by airgun source.Progress in Geophysics(in Chinese),2006,21(2) :400～407
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