渤海海域郯庐断裂带的地震层析成像特征
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摘要
渤海是连接郯庐断裂带辽宁段和山东段的重要区域,利用地震层析成像方法重建三维P波速度模型,展示了渤海海域地壳和上地幔结构的变化,揭示出郯庐断裂带的深部构造特征以及与构造活动的关系.分析表明,渤海海域的地壳结构存在明显的横向非均匀性:在辽东湾及渤海中部,郯庐断裂带附近的地壳具有双层结构,浅部为低速沉积层,地壳中、下部速度偏高,未见壳内低速层,显示了相对稳定的地壳结构特征,与现今较弱的地震活动相吻合.在渤海南部及莱州湾,郯庐断裂带受张家口-蓬莱断裂带的影响较大,全新世以来的构造活动使得这一地区的地壳结构极为复杂,成为地震活动频繁发生的重要原因之一.此外,渤海海域地壳中、下部和上地幔平均速度偏低,推测与华北克拉通破坏及地幔上涌存在一定的联系.地幔热流物质有可能沿郯庐断裂带形成的通道向上侵入,在地壳底部冷却后形成高速薄层,对于强化壳幔边界、减缓断裂带的构造活动起到了一定作用.
The Tan-Lu fault zone is a huge tectonic belt in eastern China. It extends over 3000 km long and passes through the Bohai Sea from the Shandong peninsula in the south to the Liaodong peninsula in the north. Originating from the collision of the North China block with the South China block in Indosinian period, the fault zone had experienced strike-slipping, extensional, compressional deformation and magma intrusions since Mesozoic Era. It is thought to be a continental-scale fault zone that penetrates the crust into the upper mantle. The Bohai Sea links the northern and southern segments of the Tan-Lu fault zone. Its shallow crust is covered by Cenozoic basins and bounded by a series of basement faults. Some faults may be connected to the Tan-Lu fault zone in the deep crust. Geophysically, the Tan-Lu fault zone is a Bouguer gravity boundary that separates negative anomalies in the east and positive anomalies in the west. On the magnetic map, the northern Bohai Sea is characterized by a NNE-trending positive anomaly zone. This magnetic zone becomes scattered in the southern Bohai Sea, with approximately NWW-trending anomalies parallel to the ZhangjiakouPenglai fault zone. Seismically, most earthquakes are distributed in the southern Bohai Sea, including the Ms7.4 event in 1969; very few of them took place in the northern Bohai Sea. To determine the relationship between the deep structure of the Tan-Lu fault zone and local tectonic activity, we used seismic tomography to construct a three-dimensional P-wave velocity model for the crust and upper mantle of the Bohai Sea. The data were collected from existing seismic stations around the marine area. Compared to previous tomographic studies, the crust and uppermost mantle of the Bohai Sea are well imaged with good resolution. A strong heterogeneity is observed in the crustal structure of the Bohai Sea, which shows P-wave velocity variations correlated to tectonic activity on the Tan-Lu fault zone and the Zhangjiakou-Penglai fault zone. A low-velocity sediment layer in the shallow crust and high-velocity layers in the deep crust, with no low-velocity zones in the lower crust, characterize the structure of the northern and central Bohai Sea. These features suggest a stable structure that corresponds to low earthquake activity in the northern Bohai Sea. At the same time, the Tan-Lu fault zone is truncated in the southern Bohai Sea by the NNW-trending Zhangjiakou-Penglai fault zone. Tectonic activity since the Holocene Epoch has made the crustal structure in this area very complicated and is a primary cause of frequent seismic activity. Additionally, low average velocities are observed in the deep crust and upper mantle of the Bohai Sea, which are likely to be related to mantle upwelling beneath the North China Craton. We suggest that hot material from the upper mantle intrudes into the lower crust through the Tan-Lu fault zone to form a high-velocity layer after cooling. This high-velocity layer may strengthen the crust-mantle boundary and lessen seismic activity on the fault zone.
The Tan-Lu fault zone is a huge tectonic belt in eastern China. It extends over 3000 km long and passes through the Bohai Sea from the Shandong peninsula in the south to the Liaodong peninsula in the north. Originating from the collision of the North China block with the South China block in Indosinian period, the fault zone had experienced strike-slipping, extensional, compressional deformation and magma intrusions since Mesozoic Era. It is thought to be a continental-scale fault zone that penetrates the crust into the upper mantle. The Bohai Sea links the northern and southern segments of the Tan-Lu fault zone. Its shallow crust is covered by Cenozoic basins and bounded by a series of basement faults. Some faults may be connected to the Tan-Lu fault zone in the deep crust. Geophysically, the Tan-Lu fault zone is a Bouguer gravity boundary that separates negative anomalies in the east and positive anomalies in the west. On the magnetic map, the northern Bohai Sea is characterized by a NNE-trending positive anomaly zone. This magnetic zone becomes scattered in the southern Bohai Sea, with approximately NWW-trending anomalies parallel to the ZhangjiakouPenglai fault zone. Seismically, most earthquakes are distributed in the southern Bohai Sea, including the Ms7.4 event in 1969; very few of them took place in the northern Bohai Sea. To determine the relationship between the deep structure of the Tan-Lu fault zone and local tectonic activity, we used seismic tomography to construct a three-dimensional P-wave velocity model for the crust and upper mantle of the Bohai Sea. The data were collected from existing seismic stations around the marine area. Compared to previous tomographic studies, the crust and uppermost mantle of the Bohai Sea are well imaged with good resolution. A strong heterogeneity is observed in the crustal structure of the Bohai Sea, which shows P-wave velocity variations correlated to tectonic activity on the Tan-Lu fault zone and the Zhangjiakou-Penglai fault zone. A low-velocity sediment layer in the shallow crust and high-velocity layers in the deep crust, with no low-velocity zones in the lower crust, characterize the structure of the northern and central Bohai Sea. These features suggest a stable structure that corresponds to low earthquake activity in the northern Bohai Sea. At the same time, the Tan-Lu fault zone is truncated in the southern Bohai Sea by the NNW-trending Zhangjiakou-Penglai fault zone. Tectonic activity since the Holocene Epoch has made the crustal structure in this area very complicated and is a primary cause of frequent seismic activity. Additionally, low average velocities are observed in the deep crust and upper mantle of the Bohai Sea, which are likely to be related to mantle upwelling beneath the North China Craton. We suggest that hot material from the upper mantle intrudes into the lower crust through the Tan-Lu fault zone to form a high-velocity layer after cooling. This high-velocity layer may strengthen the crust-mantle boundary and lessen seismic activity on the fault zone.
引文
1 Wan T F,Zhu H,Zhao L,et al.Formation and devolution of Tancheng-Lujiang fault zone:A review(in Chinese).Geosci J Graduate School China Univ Geosci,1996,10:159-168[万天丰,朱鸿,赵磊,等.郯庐断裂带的形成与演化:综述.现代地质,1996,10:159-168]
2 Wang X F,Li Z J,Chen B L,et al.On Tan-Lu Fault Zone(in Chinese).Beijing:Geological Publishing House,2000.1-374[王小凤,李中坚,陈柏林,等.郯庐断裂带.北京:地质出版社,2000.1-374]
3 Yu Z,Wu S,Zhou D,et al.Seismic profiles across the middle Tan-Lu fault zone in Laizhou Bay,Bohai Sea,eastern China.J Asian Earth Sci,2008,33,383-394
4 Li X S,Zhao Y X,Liu B H,et al.Structural deformation and fault activity of the Tan-Lu Fault zone in the Bohai Sea since the late Pleistocene.Chin Sci Bull,2010,55:1908-1916[李西双,赵月霞,刘保华,等.郯庐断裂带渤海段晚更新世以来的浅层构造变形和活动性.科学通报,2010,55:684-692]
5 Tang L J,Chen X Y,Zhou X H,et al.Structure analysis of Tan-Lu fault zone in the Bohai Sea(in Chinese).J Southwest Petrol Univ(Sci Techn Ed),2011,33:170-176[汤良杰,陈绪云,周心怀,等.渤海海域郯庐断裂带构造解析.西南石油大学学报:自然科学版,2011,33:170-176]
6 Huang L,Liu C Y,Kusky T M.Cenozoic evolution of the Tan-Lu Fault Zone(East China):Constraints from seismic data.Gondwana Res,2015,28:1079-1095
7 Zhu G,Hu W,Song L,et al.Quaternary activity along the Tan-Lu fault zone in the Bohai Bay,East China:Evidence from seismic profiles.J Asian Earth Sci,2015,114:5-7
8 Qi J,Zhou X,Deng R,et al.Structural characteristics of the Tan-Lu fault zone in Cenozoic basins offshore the Bohai Sea.Sci China Ser D-Earth Sci,2008,51(Suppl 2):20-31[漆家福,邓荣敬,周心怀,等.渤海海域新生代盆地中的郯庐断裂带构造.中国科学D辑:地球科学,2008,38(增刊I):19-29]
9 Qi J,Yang Q.Cenozoic structural deformation and dynamic processes of the Bohai Bay basin province,China.Mar Petrol Geol,2010,27:757-771
10 Xu J,Gao Z W,Sun J B,et al.Analysis of structures in 1969 Bohai Sea Ms 7.4 earthquake area and discussion about the causative structure(in Chinese).Earthq Res China,2001,17:121-133[徐杰,高战武,孙建宝,等.1969年渤海7.4级地震区地质构造和发震构造的初步研究.中国地震,2001,17:121-133]
11 Fu Z,Liu J,Liu G.On the long-term seismic hazard analysis in the Zhangjiakou-Penglai seismotectonic zone,China.Tectonophysics,2004,390:75-83
12 Qi J F,Zhou X H,Wang Q S.Structural model and Cenozoic kinematics of Tan-Lu deep fracture zone in Bohai Sea area(in Chinese).Geol China,2010,37:1231-1242[漆家福,周心怀,王谦身.渤海海域中郯庐深断裂带的结构模型及新生代运动学.中国地质,2010,37:1231-1242]
13 Jiang D D,Jiang W W,Hu W J.Study of crustal structure and geodynamic characteristics around the Bohai Sea area(in Chinese).Prog Geophys,2013,28:1729-1738[姜迪迪,江为为,胡卫剑.环渤海地区地壳结构及其动力学特征研究.地球物理学进展,2013,28:1729-1738]
14 Qiu N S,Wei G,Li C C,et al.Distribution features of current geothermal field in the Bohai Sea waters(in Chinese).Oil Gas Geol,2009,30:412-419[邱楠生,魏刚,李翠翠,等.渤海海域现今地温场分布特征.石油与天然气地质,2009,30:412-419]
15 Li Z W,Xu Y,Hao T Y,et al.Seismic tomography and velocity structure in the crust and upper mantle around Bohai Sea area(in Chinese).Chin J Geophys,2006,49:797-804[李志伟,胥颐,郝天珧,等.环渤海地区的地震层析成像与地壳上地幔结构.地球物理学报,2006,49:797-804]
16 Zhang L,Liu J S,Hao T Y,et al.Seismic tomography of the crust and upper mantle in the Bohai Bay Basin and its adjacent regions.Sci China Ser D-Earth Sci,2007,50:1810-1822[张岭,刘劲松,郝天珧,等.渤海湾盆地及其邻域地区地壳与上地幔层析成像.中国科学D辑:地球科学,2007,37:1444-1455]
17 Hao T,You Q,Liu L,et al.Joint land-sea seismic survey and research on the deep structures of the Bohai Sea areas.Acta Oceanol Sin,2013,32:13-24
18 Liu L,Hao T,LüC,et al.Crustal structure of Bohai Sea and adjacent area(North China)from two onshore-offshore wide-angle seismic survey lines.J Asian Earth Sci,2015,98:457-469
19 Hu W,Zhu G,Yan L J,et al.Analysis of relationship between seismic activity and crust electrical textures for the central segment of the Tan-Lu fault zone(in Chinese).Geol Rev,2014,60:80-90[胡惟,朱光,严乐佳,等.郯庐断裂带中段地震活动性与深部地壳电性结构关系的探讨.地质评论,2014,60:80-90]
20 Kennett B L N,Engdahl E R,Buland R.Constraints on seismic velocities in the Earth from traveltimes.Geophys J Int,1995,122:108-124
21 Zhao D,Hasegawa A,Horiuchi S.Tomographic imaging of P and S wave velocity structure beneath northeastern Japan.J Geophys Res,1992,97:19909-19928
22 Koketsu K,Sekine S.Pseudo-bending method for three-dimensional seismic ray tracing in a spherical earth with discontinuities.Geophys J Int,1998,132:339-346
23 Hao T Y,Hu W J,Xin J,et al.The Moho depth map(1:5000000)in the land and sea of China and adjacent areas and its geological implications(in Chinese).Chin J Geophys,2014,57:3869-3883[郝天珧,胡为剑,刑健,等.中国海陆1:500万莫霍面深度图及其所反映的地质内涵.地球物理学报,2014,57:3869-3883]
24 Paige C C,Saunders M A.LSQR:An algorithm for sparse linear equations and sparse least squares.ACM T Math Software,1982,8:43-71
25 Hou G T,Qian X L,Cai D S.Cretaceous-Paleogene rifting in the Bohai Sea and western Shandong:Geochemical evidence from volcanic rocks(in Chinese).Chin J Geol,2003,38:13-21[侯贵廷,钱祥麟,蔡东升.渤海-鲁西地区白垩-早第三纪裂谷活动-火山岩的地球化学证据.地质科学,2003,38:13-21]
26 Liu S,Feng C,Hu R.Zircon U-Pb geochronological,geochemical,and Sr-Nd isotope data for Early Cretaceous mafic dykes in the Tancheng-Lujiang Fault area of the Shandong Province,China:Constraints on the timing of magmatism and magma genesis.J Asian Earth Sci,2015,98:247-260
27 Xu J,Zhou B G,Ji F J,et al.A primary study on the neotectonic pattern of the Bohai area in China(in Chinese).Acta Petrol Sin,2011,32:442-449[徐杰,周本钢,计风桔,等.渤海地区新构造格局.石油学报,2011,32:442-449]
28 Nie W Y,Zhu Z P,Zhang X K,et al.The crustal-mantle tectonics and its velocity structure revealed by the refraction profile passing through the west edge of the Zhangjiakou-Bohai seismic belt(in Chinese).J Seismol Res,1998,21:94-102[聂文英,祝治平,张先康,等.穿过张家口-渤海地震带西缘的折射剖面所揭示的地壳上地幔构造与速度结构.地震研究,1998,21:94-102]
29 Lai X L,Zhang X K,Cheng S X,et al.Study on crust mantle transitional zone in west margin of Zhangjiakou-Bohai fault belt(in Chinese).Chin J Geophys,2004,47:798-804[赖晓玲,张先康,成双喜,等.张家口-渤海断裂带西缘壳幔过渡带研究.地球物理学报,2004,47:798-804]
30 Zhu R X,Xu Y G,Zhu G,et al.Destruction of the North China Craton.Sci China Earth Sci,2012,55:1565-1587[朱日祥,徐义刚,朱光,等.华北克拉通破坏.中国科学:地球科学,2012,42:1135-1159
31 Hou G,Hari K R.Mesozoic-Cenozoic extension of the Bohai Sea:Contribution to the destruction of North China Craton.Front Earth Sci,2014,8:202-215
32 Jia S,Wang F,Tian X,et al.Crustal structure and tectonic study of North China Craton from a long deep seismic sounding profile.Tectonophysics,2014,627:48-56
33 Chen L,Zheng T,Xu W.A thinned lithospheric image of the Tanlu Fault Zone,eastern China:Constructed from wave equation based receiver function migration.J Geophys Res,2006,111:B09312,doi:10.1029/2005JB003974
2 Wang X F,Li Z J,Chen B L,et al.On Tan-Lu Fault Zone(in Chinese).Beijing:Geological Publishing House,2000.1-374[王小凤,李中坚,陈柏林,等.郯庐断裂带.北京:地质出版社,2000.1-374]
3 Yu Z,Wu S,Zhou D,et al.Seismic profiles across the middle Tan-Lu fault zone in Laizhou Bay,Bohai Sea,eastern China.J Asian Earth Sci,2008,33,383-394
4 Li X S,Zhao Y X,Liu B H,et al.Structural deformation and fault activity of the Tan-Lu Fault zone in the Bohai Sea since the late Pleistocene.Chin Sci Bull,2010,55:1908-1916[李西双,赵月霞,刘保华,等.郯庐断裂带渤海段晚更新世以来的浅层构造变形和活动性.科学通报,2010,55:684-692]
5 Tang L J,Chen X Y,Zhou X H,et al.Structure analysis of Tan-Lu fault zone in the Bohai Sea(in Chinese).J Southwest Petrol Univ(Sci Techn Ed),2011,33:170-176[汤良杰,陈绪云,周心怀,等.渤海海域郯庐断裂带构造解析.西南石油大学学报:自然科学版,2011,33:170-176]
6 Huang L,Liu C Y,Kusky T M.Cenozoic evolution of the Tan-Lu Fault Zone(East China):Constraints from seismic data.Gondwana Res,2015,28:1079-1095
7 Zhu G,Hu W,Song L,et al.Quaternary activity along the Tan-Lu fault zone in the Bohai Bay,East China:Evidence from seismic profiles.J Asian Earth Sci,2015,114:5-7
8 Qi J,Zhou X,Deng R,et al.Structural characteristics of the Tan-Lu fault zone in Cenozoic basins offshore the Bohai Sea.Sci China Ser D-Earth Sci,2008,51(Suppl 2):20-31[漆家福,邓荣敬,周心怀,等.渤海海域新生代盆地中的郯庐断裂带构造.中国科学D辑:地球科学,2008,38(增刊I):19-29]
9 Qi J,Yang Q.Cenozoic structural deformation and dynamic processes of the Bohai Bay basin province,China.Mar Petrol Geol,2010,27:757-771
10 Xu J,Gao Z W,Sun J B,et al.Analysis of structures in 1969 Bohai Sea Ms 7.4 earthquake area and discussion about the causative structure(in Chinese).Earthq Res China,2001,17:121-133[徐杰,高战武,孙建宝,等.1969年渤海7.4级地震区地质构造和发震构造的初步研究.中国地震,2001,17:121-133]
11 Fu Z,Liu J,Liu G.On the long-term seismic hazard analysis in the Zhangjiakou-Penglai seismotectonic zone,China.Tectonophysics,2004,390:75-83
12 Qi J F,Zhou X H,Wang Q S.Structural model and Cenozoic kinematics of Tan-Lu deep fracture zone in Bohai Sea area(in Chinese).Geol China,2010,37:1231-1242[漆家福,周心怀,王谦身.渤海海域中郯庐深断裂带的结构模型及新生代运动学.中国地质,2010,37:1231-1242]
13 Jiang D D,Jiang W W,Hu W J.Study of crustal structure and geodynamic characteristics around the Bohai Sea area(in Chinese).Prog Geophys,2013,28:1729-1738[姜迪迪,江为为,胡卫剑.环渤海地区地壳结构及其动力学特征研究.地球物理学进展,2013,28:1729-1738]
14 Qiu N S,Wei G,Li C C,et al.Distribution features of current geothermal field in the Bohai Sea waters(in Chinese).Oil Gas Geol,2009,30:412-419[邱楠生,魏刚,李翠翠,等.渤海海域现今地温场分布特征.石油与天然气地质,2009,30:412-419]
15 Li Z W,Xu Y,Hao T Y,et al.Seismic tomography and velocity structure in the crust and upper mantle around Bohai Sea area(in Chinese).Chin J Geophys,2006,49:797-804[李志伟,胥颐,郝天珧,等.环渤海地区的地震层析成像与地壳上地幔结构.地球物理学报,2006,49:797-804]
16 Zhang L,Liu J S,Hao T Y,et al.Seismic tomography of the crust and upper mantle in the Bohai Bay Basin and its adjacent regions.Sci China Ser D-Earth Sci,2007,50:1810-1822[张岭,刘劲松,郝天珧,等.渤海湾盆地及其邻域地区地壳与上地幔层析成像.中国科学D辑:地球科学,2007,37:1444-1455]
17 Hao T,You Q,Liu L,et al.Joint land-sea seismic survey and research on the deep structures of the Bohai Sea areas.Acta Oceanol Sin,2013,32:13-24
18 Liu L,Hao T,LüC,et al.Crustal structure of Bohai Sea and adjacent area(North China)from two onshore-offshore wide-angle seismic survey lines.J Asian Earth Sci,2015,98:457-469
19 Hu W,Zhu G,Yan L J,et al.Analysis of relationship between seismic activity and crust electrical textures for the central segment of the Tan-Lu fault zone(in Chinese).Geol Rev,2014,60:80-90[胡惟,朱光,严乐佳,等.郯庐断裂带中段地震活动性与深部地壳电性结构关系的探讨.地质评论,2014,60:80-90]
20 Kennett B L N,Engdahl E R,Buland R.Constraints on seismic velocities in the Earth from traveltimes.Geophys J Int,1995,122:108-124
21 Zhao D,Hasegawa A,Horiuchi S.Tomographic imaging of P and S wave velocity structure beneath northeastern Japan.J Geophys Res,1992,97:19909-19928
22 Koketsu K,Sekine S.Pseudo-bending method for three-dimensional seismic ray tracing in a spherical earth with discontinuities.Geophys J Int,1998,132:339-346
23 Hao T Y,Hu W J,Xin J,et al.The Moho depth map(1:5000000)in the land and sea of China and adjacent areas and its geological implications(in Chinese).Chin J Geophys,2014,57:3869-3883[郝天珧,胡为剑,刑健,等.中国海陆1:500万莫霍面深度图及其所反映的地质内涵.地球物理学报,2014,57:3869-3883]
24 Paige C C,Saunders M A.LSQR:An algorithm for sparse linear equations and sparse least squares.ACM T Math Software,1982,8:43-71
25 Hou G T,Qian X L,Cai D S.Cretaceous-Paleogene rifting in the Bohai Sea and western Shandong:Geochemical evidence from volcanic rocks(in Chinese).Chin J Geol,2003,38:13-21[侯贵廷,钱祥麟,蔡东升.渤海-鲁西地区白垩-早第三纪裂谷活动-火山岩的地球化学证据.地质科学,2003,38:13-21]
26 Liu S,Feng C,Hu R.Zircon U-Pb geochronological,geochemical,and Sr-Nd isotope data for Early Cretaceous mafic dykes in the Tancheng-Lujiang Fault area of the Shandong Province,China:Constraints on the timing of magmatism and magma genesis.J Asian Earth Sci,2015,98:247-260
27 Xu J,Zhou B G,Ji F J,et al.A primary study on the neotectonic pattern of the Bohai area in China(in Chinese).Acta Petrol Sin,2011,32:442-449[徐杰,周本钢,计风桔,等.渤海地区新构造格局.石油学报,2011,32:442-449]
28 Nie W Y,Zhu Z P,Zhang X K,et al.The crustal-mantle tectonics and its velocity structure revealed by the refraction profile passing through the west edge of the Zhangjiakou-Bohai seismic belt(in Chinese).J Seismol Res,1998,21:94-102[聂文英,祝治平,张先康,等.穿过张家口-渤海地震带西缘的折射剖面所揭示的地壳上地幔构造与速度结构.地震研究,1998,21:94-102]
29 Lai X L,Zhang X K,Cheng S X,et al.Study on crust mantle transitional zone in west margin of Zhangjiakou-Bohai fault belt(in Chinese).Chin J Geophys,2004,47:798-804[赖晓玲,张先康,成双喜,等.张家口-渤海断裂带西缘壳幔过渡带研究.地球物理学报,2004,47:798-804]
30 Zhu R X,Xu Y G,Zhu G,et al.Destruction of the North China Craton.Sci China Earth Sci,2012,55:1565-1587[朱日祥,徐义刚,朱光,等.华北克拉通破坏.中国科学:地球科学,2012,42:1135-1159
31 Hou G,Hari K R.Mesozoic-Cenozoic extension of the Bohai Sea:Contribution to the destruction of North China Craton.Front Earth Sci,2014,8:202-215
32 Jia S,Wang F,Tian X,et al.Crustal structure and tectonic study of North China Craton from a long deep seismic sounding profile.Tectonophysics,2014,627:48-56
33 Chen L,Zheng T,Xu W.A thinned lithospheric image of the Tanlu Fault Zone,eastern China:Constructed from wave equation based receiver function migration.J Geophys Res,2006,111:B09312,doi:10.1029/2005JB003974