岷县漳县M_S6.6地震震源区地壳速度结构特征初步研究
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摘要
利用距离2013年岷县漳县地震最近的固定台站岷县台2008-2009年的远震接收函数,确定了该地震震源区及临近区域的地壳厚度和波速比。结果表明:岷县台下方地壳速度结构的横向非均匀性较强,各方位接收函数差异较大,特别是震源区与临近区域存在明显的差别。临近区域的中下地壳存在明显的低速层,而震源区中下地壳中存在明显的高速区;且震源区地壳平均波速比为1.76,上地壳的波速比仅为1.62。据此推断:震源区是坚硬的上地壳覆盖在较软的中下地壳之上,岷县漳县地震破裂有可能是下地壳流的活动导致上地壳的破裂。
An MS6.6 earthquake occurred at the junction of Minxian and Zhangxian on July 22,2013,at 7:45in the northern section of the North-South seismic zone in the southeast region of Gansu Province.This area is a moderate-strong earthquake-prone region in which the Minxian MS5.2 earthquake and Minxian-Zhuoni MS5.0 earthquake also occurred in 2003and 2004,respectively.In this study,we analyze teleseismic data recorded in 2008-2009 by Minxian station,which is the permanent station in closest proximity to the Minxian-Zhangxian earthquake.Receiver functions aligned by azimuth indicate obvious heterogeneity beneath the Minxian station;observed receiver functions of Minxian station vary according to azimuth.That is,receiver functions of the seismic source area and adjacent areas show obvious differences.In the seismic source area,the receiver function is clearly apositive signal of approximately 1.5s,which indicates that a high velocity zone is present in the middle-lower crust.In the adjacent areas,the receiver function is clearly a negative signal of approximately 1.5s,indicating the presence of a lower velocity zone in the middle-lower crust.This phenomenon shows obvious crustal structure differences between the seismic source area and adjacent areas.In addition,we used the H-kstacking method of receiver functions to determine the crustal thickness and wave velocity ratio of the two areas.The results show crust thicknesses of 45km and 47km and wave velocity ratios of 1.76and 1.69in the source area and adjacent area,respectively.Therefore,obvious differences in crustal velocity structure appear between the two areas.In the seismic source area,the Ps,PpSs/PsPs clearly indicates crustal discontinuity.Therefore,the H-k stacking method of receiver functions was used to determine the depth of the discontinuity surface and the wave ratio velocity.The H-k stacking results showed an upper crustal thickness of 15km and a wave velocity ratio of 1.62.We estimated the middle-lower crustal thickness and wave velocity ratio to be 30km and 1.84,respectively.Therefore,the soft middle-lower crust is covered by the hard upper crust at the top in the source area.This type of small-scale material inhomogeneity may be an important part of the deep structure of the Minxian-Zhangxian earthquake background.We estimate that the rupture of the Minxian-Zhangxian earthquake may have been attributed to lower crustal flow leading to rupture of the upper crust.
An MS6.6 earthquake occurred at the junction of Minxian and Zhangxian on July 22,2013,at 7:45in the northern section of the North-South seismic zone in the southeast region of Gansu Province.This area is a moderate-strong earthquake-prone region in which the Minxian MS5.2 earthquake and Minxian-Zhuoni MS5.0 earthquake also occurred in 2003and 2004,respectively.In this study,we analyze teleseismic data recorded in 2008-2009 by Minxian station,which is the permanent station in closest proximity to the Minxian-Zhangxian earthquake.Receiver functions aligned by azimuth indicate obvious heterogeneity beneath the Minxian station;observed receiver functions of Minxian station vary according to azimuth.That is,receiver functions of the seismic source area and adjacent areas show obvious differences.In the seismic source area,the receiver function is clearly apositive signal of approximately 1.5s,which indicates that a high velocity zone is present in the middle-lower crust.In the adjacent areas,the receiver function is clearly a negative signal of approximately 1.5s,indicating the presence of a lower velocity zone in the middle-lower crust.This phenomenon shows obvious crustal structure differences between the seismic source area and adjacent areas.In addition,we used the H-kstacking method of receiver functions to determine the crustal thickness and wave velocity ratio of the two areas.The results show crust thicknesses of 45km and 47km and wave velocity ratios of 1.76and 1.69in the source area and adjacent area,respectively.Therefore,obvious differences in crustal velocity structure appear between the two areas.In the seismic source area,the Ps,PpSs/PsPs clearly indicates crustal discontinuity.Therefore,the H-k stacking method of receiver functions was used to determine the depth of the discontinuity surface and the wave ratio velocity.The H-k stacking results showed an upper crustal thickness of 15km and a wave velocity ratio of 1.62.We estimated the middle-lower crustal thickness and wave velocity ratio to be 30km and 1.84,respectively.Therefore,the soft middle-lower crust is covered by the hard upper crust at the top in the source area.This type of small-scale material inhomogeneity may be an important part of the deep structure of the Minxian-Zhangxian earthquake background.We estimate that the rupture of the Minxian-Zhangxian earthquake may have been attributed to lower crustal flow leading to rupture of the upper crust.
引文
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[9]丁志峰,何正勤,孙卫国,等.青藏高原东部及其边缘地区的地壳上地幔三维速度结构[J].地球物理学报,1999,42(2):197-205.DING Zhi-feng,HE Zheng-qin,SUN Wei-guo,et al.3-D Crust and Upper Mantle Velocity Structure in Eastern Tibetan Plateau and Its Surrounding Areas[J].Chinese Journal of Geophysics,1999,42(2):197-205.(in Chinese)
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[11]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 Yuan-sheng,ZHOU Min-du,RONG Dai-lu,et al.3-D Velocity Structure in the Central-eastern Part of Qilian Shan[J].Acta Seismologica Sinica,2004,26(3):247-255.(in Chinese)
[12]郭飚,刘启元,陈九辉,等.青藏高原东北缘-鄂尔多斯地壳上地幔地震层析成像研究[J].地球物理学报,2004,47(5):790-797.GUO Biao,LIU Qi-yuan,CHEN Jiu-hui,et al.Seismic Tomographic Imaging of the Crust and Upper Mantle Beneath the Northeastern Edge of the Qinghai-Xizang Plateau and the Ordos Area[J].Chinese Journal of Geophysics,2004,47(5):790-797.(in Chinese)
[13]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 Min-du,ZHANG Yuan-sheng,SHI Ya-miu,et al.Three-dimensional Crustal Velocity Structure in the Northeastern Margin of the Qinghai-Tibetan Plateau[J].Progress in Geophysics,2006,21(1):127-134.(in Chinese)
[14]王周元.甘肃地区分层地壳结构[J].西北地震学报,1984,6(3):84-91.WANG Zhou-yuan.Layered Crustal Structure in Gansu Region[J].Northwestern Seismological Journal,1984,6(3):84-91.(in Chinese)
[15]王周元,范世宏,姬凤英,等.甘肃地区地壳速度的非均匀分布[J].西北地震学报,1996,18(2):18-25.WANG Zhou-yuan,FAN Shi-hong,JI Feng-ying,et al.The Inhomogeneity of Crustal Velocity in Gansu Region[J].Northwestern Seismological Journal,1996,18(2):18-25.(in Chinese)
[16]陈九辉,刘启元,李顺成,等.青藏高原东北缘-鄂尔多斯地块地壳上地幔S波速度结构[J].地球物理学报,2005,48(2):333-342.CHEN Jiu-hui,LIU Qi-yuan,LI Shun-cheng,et al.Crust and Upper Mantle S-wave Velocity Structure Across Northeastern Tibetan Plateau and Ordos Block[J].Chinese Journal of Geophysics,2005,48(2):333-342.(in Chinese)
[17]李永华,吴庆举,安张辉,等.青藏高原东北缘地壳S波速度结构与泊松比及其意义[J].地球物理学报,2006,49(5):1359-1368.LI Yong-hua,WU Qin-ju,AN Zhang-hui,et al.The Poisson Ratio and Crustal Structure Across the NE Tibetan Plateau Determined from Receiver Functions[J].Chinese Journal of Geophysics,2006,49(5):1359-1368.(in Chinese)
[18]安张辉,吕子岚,杜学彬,等.甘肃省各数字测震台下方地壳速度结构研究[J].西北地震学报,2008,30(3):61-66.AN Zhang-hui,LüZi-lan,DU Xue-bin,et al.The Crustal Structure Beneath Digital Seismic Stations in Gansu Province[J].Northwestern Seismological Journal,2008,30(3):61-66.(in Chinese)
[19]SHEN Xu-zhang,MEI Xiu-ping,ZHANG Yuan-sheng.The Crustal and Upper-Mantle Structures Beneath the Northeastern Margin of Tibet[J].Bulletin of the Seismological of America,2011,101(6):2782-2795.
[20]Zhu L P,Kanamori H.Moho Depth Variation in Southern California from Teleseismic Receiver Function[J].J.Geophs.Res.,2000,105(B2):2969-2980.
[21]李清河.天水地区S波速度结构[J].西北地震学报,1991,13(增刊):48-54.LI Qing-he.The Velocity Structure of S-wave in Tianshui Area[J].Northwestern Seismological Journal,1991,13(Supp):48-54.(in Chinese)
[22]李少华,王彦宾,梁子斌,等.甘肃东南部地壳速度结构的区域地震波形反演[J].地球物理学报,2012,55(4):1186-1197.LI Shao-hua,WANG Yan-bin,LIANG Zi-bin,et al.Crustal Structure in Southeastern Gansu from Regional Seismic Waveform Inversion[J].Chinese Journal of Geophysics,2012,55(4):1186-1197.(in Chinese)
[2]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 Xiang-yi,ZHOU Min-du,GUO Jian-kang,et al.The Crustal Velocity Structure in Lingtai-Amuquhu profile[J].Northwestern Seismological Journal,1991,13(S1):29-36.(in Chinese)
[3]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 Qing-he,GUO Jian-kang,ZHOU Min-du,et al.The Velocity Structure of Chengxian-Xiji Profile[J].Northwestern Seismological Journal,1991,13(Supp):37-43.(in Chinese)
[4]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 Song-lin,ZHANG Xian-kang,ZHANG Cheng-ke,et al.A Preliminary Study on the Crustal Velocity Structure of Maqin-Lanzhou-Jingbian by Means of Deep Seismic Sounding Profile[J].Chinese Journal of Geophysics,2002,45(2):210-217.(in Chinese)
[5]张少泉,武利钧,郭建民,等.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):349-361.ZHANG Shao-quan,WU Li-jun,GUO Jian-min,et al.An Interpretation of the DSS Data on Menyuan-PingliangWeinan Profile in West China[J].Chinese Journal of Geophysics,1985,28(5):349-361.(in Chinese)
[6]王双绪,张希,祝意青,等.南北地震带北段强震形变异常特征与预测指标研究[J].西北地震学报,2012,34(2):105-113.WANG Shuang-xu,ZHANG Xi,ZHU Yi-qing,et al.Study on the Characteristics of Strong Earthquake Deformation Anomalies and Forecasting Index in the North Segment of the South-north Seismic Belt of China[J].Northwestern Seismological Journal,2012,34(2):105-113.(in Chinese)
[7]王椿镛.中国岩石层结构研究的回顾与展望[J].地球物理学报,1997,40(增刊):82-109.WANG Chun-yong.Review and Prospect on Lithospheric Structure study in China[J].Chinese Journal of Geophysics,1997,40(Supp):82-109.(in Chinese)
[8]张辉,王熠熙,冯建刚.甘东南地区地壳介质各向异性特征[J].西北地震学报,2011,33(2):111-116.ZHANG Hui,WANG Yi-xi,FENG Jian-gang.Seismic Anisotropy in the Crust in Southeastern Area of Gansu Province[J].Northwestern Seismological Journal,2011,33(2):111-116.(in Chinese)
[9]丁志峰,何正勤,孙卫国,等.青藏高原东部及其边缘地区的地壳上地幔三维速度结构[J].地球物理学报,1999,42(2):197-205.DING Zhi-feng,HE Zheng-qin,SUN Wei-guo,et al.3-D Crust and Upper Mantle Velocity Structure in Eastern Tibetan Plateau and Its Surrounding Areas[J].Chinese Journal of Geophysics,1999,42(2):197-205.(in Chinese)
[10]许忠淮,汪素云,裴顺平.青藏高原东北缘地区Pn波速度的横向变化[J].地震学报,2003,25(1):25-31.XU Zhong-huai,WANG Su-yun,PEI Shun-ping.Lateral Variation of Pn Velocity Beneath Northeastern Marginal Region of Qingzang Plateau[J].Acta Seismologica Sinica,2003,25(1):25-31.(in Chinese)
[11]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 Yuan-sheng,ZHOU Min-du,RONG Dai-lu,et al.3-D Velocity Structure in the Central-eastern Part of Qilian Shan[J].Acta Seismologica Sinica,2004,26(3):247-255.(in Chinese)
[12]郭飚,刘启元,陈九辉,等.青藏高原东北缘-鄂尔多斯地壳上地幔地震层析成像研究[J].地球物理学报,2004,47(5):790-797.GUO Biao,LIU Qi-yuan,CHEN Jiu-hui,et al.Seismic Tomographic Imaging of the Crust and Upper Mantle Beneath the Northeastern Edge of the Qinghai-Xizang Plateau and the Ordos Area[J].Chinese Journal of Geophysics,2004,47(5):790-797.(in Chinese)
[13]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 Min-du,ZHANG Yuan-sheng,SHI Ya-miu,et al.Three-dimensional Crustal Velocity Structure in the Northeastern Margin of the Qinghai-Tibetan Plateau[J].Progress in Geophysics,2006,21(1):127-134.(in Chinese)
[14]王周元.甘肃地区分层地壳结构[J].西北地震学报,1984,6(3):84-91.WANG Zhou-yuan.Layered Crustal Structure in Gansu Region[J].Northwestern Seismological Journal,1984,6(3):84-91.(in Chinese)
[15]王周元,范世宏,姬凤英,等.甘肃地区地壳速度的非均匀分布[J].西北地震学报,1996,18(2):18-25.WANG Zhou-yuan,FAN Shi-hong,JI Feng-ying,et al.The Inhomogeneity of Crustal Velocity in Gansu Region[J].Northwestern Seismological Journal,1996,18(2):18-25.(in Chinese)
[16]陈九辉,刘启元,李顺成,等.青藏高原东北缘-鄂尔多斯地块地壳上地幔S波速度结构[J].地球物理学报,2005,48(2):333-342.CHEN Jiu-hui,LIU Qi-yuan,LI Shun-cheng,et al.Crust and Upper Mantle S-wave Velocity Structure Across Northeastern Tibetan Plateau and Ordos Block[J].Chinese Journal of Geophysics,2005,48(2):333-342.(in Chinese)
[17]李永华,吴庆举,安张辉,等.青藏高原东北缘地壳S波速度结构与泊松比及其意义[J].地球物理学报,2006,49(5):1359-1368.LI Yong-hua,WU Qin-ju,AN Zhang-hui,et al.The Poisson Ratio and Crustal Structure Across the NE Tibetan Plateau Determined from Receiver Functions[J].Chinese Journal of Geophysics,2006,49(5):1359-1368.(in Chinese)
[18]安张辉,吕子岚,杜学彬,等.甘肃省各数字测震台下方地壳速度结构研究[J].西北地震学报,2008,30(3):61-66.AN Zhang-hui,LüZi-lan,DU Xue-bin,et al.The Crustal Structure Beneath Digital Seismic Stations in Gansu Province[J].Northwestern Seismological Journal,2008,30(3):61-66.(in Chinese)
[19]SHEN Xu-zhang,MEI Xiu-ping,ZHANG Yuan-sheng.The Crustal and Upper-Mantle Structures Beneath the Northeastern Margin of Tibet[J].Bulletin of the Seismological of America,2011,101(6):2782-2795.
[20]Zhu L P,Kanamori H.Moho Depth Variation in Southern California from Teleseismic Receiver Function[J].J.Geophs.Res.,2000,105(B2):2969-2980.
[21]李清河.天水地区S波速度结构[J].西北地震学报,1991,13(增刊):48-54.LI Qing-he.The Velocity Structure of S-wave in Tianshui Area[J].Northwestern Seismological Journal,1991,13(Supp):48-54.(in Chinese)
[22]李少华,王彦宾,梁子斌,等.甘肃东南部地壳速度结构的区域地震波形反演[J].地球物理学报,2012,55(4):1186-1197.LI Shao-hua,WANG Yan-bin,LIANG Zi-bin,et al.Crustal Structure in Southeastern Gansu from Regional Seismic Waveform Inversion[J].Chinese Journal of Geophysics,2012,55(4):1186-1197.(in Chinese)
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