川滇活动地块东南边界基底结构——盐源—西昌—昭觉—马湖深地震测深剖面结果
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摘要
在川滇活动地块东南边界区域完成了盐源—西昌—昭觉—马湖深地震宽角反射/折射探测剖面.利用该剖面获得的Pg初至折射波走时,采用走时特征分析、有限差分反演、时间项反演等方法,获得了沿剖面的基底P波速度结构和基底界面构造图像.结果表明,研究区基底结构呈现强烈的非均匀性,不同构造区显示出不同的地壳变形特征.盐源盆地盖层表现为推覆逆冲变形,基底为康滇地轴的基底,表现为刚性.金河盆地—西昌中生代盆地盖层表现为褶皱、冲断和隆升变形,基底断裂重新错断、破碎变形.大凉山地区以基底断裂重新错动、破碎变形为主.盐源推覆构造由盖层低速体、其下向西缓倾的基底面和高速基底构成,它以向西缓倾的金河—箐河断裂为前锋向北东逆冲推覆,推覆构造滑脱面则是向西缓倾的基底面,深度为2—3 km,并在金河盆地西缘接近地表.金河、西昌中生代盆地基底起伏较大,埋深明显大于两侧的盐源盆地和大凉山地区,最大深度约6 km.上地壳断裂被成像为低速条带或速度梯度带,穿过断裂的走时曲线出现反向段特征,断裂两侧基底埋深存在明显的变化.安宁河、则木河和大凉山断裂是研究区断裂特征明显的断裂.其中,安宁河、则木河断裂表现为速度等值线强烈下凹的低速条带,与两侧形成显著的速度差异,倾向北东;大凉山断裂表现为狭窄条带内速度结构急剧变化,由两支组成:西支倾向南西,东支倾向北东;磨盘山断裂倾向南西;黑水河断裂分为两支:西支倾向南西,东支倾向北东;西昌中生代盆地东缘断裂倾向南西.
Yanyuan——Xichang——Zhaojue——Mahu wide-angle reflection/refraction deep seismic profile has been completed in the southeastern boundary region of Sichuan-Yunnan active block.The images of P-wave velocity structure and the basement interface along the profile are obtained by interpreting the arrival times of refracted Pg wave and using finite difference inversion and time-term inversion.The result shows that the basement structure is significantly inhomogeneous and different tectonic zones reveal different deformation features.The Yanyuan basin is characterized by caprock nappe thrust deformation,while its basement is the rigid base of Kangdian axis.In the range of Jinhe basin to Xichang Mesozoic basin,the caprock deformation is characterized by fold,thrust and uplift,while the basement reveals renewed dislocation and crush deformation of preexisting fault.In Daliang Mountain region deformation is mainly represented by renewed dislocation and crushing of basement fault.Yanyuan nappe structure is composed of caprock low-velocity body,gently west-dipping basement interface and deep high-velocity basement.It thrusts toward northeast with the west-dipping Jinhe——Qinghe fault zone as the nappe front.The detachment surface of the nappe structure is a gently west-dipping basement interface,which is 2—3 km deep and outcrops in the west margin of Jinhe basin.The basement depth varies generally and changes more significantly in the range from Jinhe basin to Xichang basin than in its western and eastern adjacent areas,with maximum depth being about 6 km there.The faults in the upper crust behave as the low velocity zones or velocity gradient zones,while the travel-time curves of Pg wave through the faults occur variation in negative slope and there is significant difference in the depth of basement on both sides of the faults.Faulting feature can be clearly seen on Anninghe fault,Zemuhe fault and Daliangshan fault.Anninghe fault and Zemuhe fault behave as low velocity belts,where strong concave velocity isolines appear and sharp velocity differences as compared with their two sides can be distinguished.The two faults both dip northeastward.Daliangshan fault is composed of two branches,with the west branch dipping southwestward and the east one northeastward,being characterized by rapid velocity variation structure in a narrow belt.Mopan-shan fault dips toward southwest.Heishuihe fault is divided into two branches,with west one dipping toward southwest and east one dipping toward northeast.The east edge fault of Xichang Mesozoic basin dips toward southwest.
Yanyuan——Xichang——Zhaojue——Mahu wide-angle reflection/refraction deep seismic profile has been completed in the southeastern boundary region of Sichuan-Yunnan active block.The images of P-wave velocity structure and the basement interface along the profile are obtained by interpreting the arrival times of refracted Pg wave and using finite difference inversion and time-term inversion.The result shows that the basement structure is significantly inhomogeneous and different tectonic zones reveal different deformation features.The Yanyuan basin is characterized by caprock nappe thrust deformation,while its basement is the rigid base of Kangdian axis.In the range of Jinhe basin to Xichang Mesozoic basin,the caprock deformation is characterized by fold,thrust and uplift,while the basement reveals renewed dislocation and crush deformation of preexisting fault.In Daliang Mountain region deformation is mainly represented by renewed dislocation and crushing of basement fault.Yanyuan nappe structure is composed of caprock low-velocity body,gently west-dipping basement interface and deep high-velocity basement.It thrusts toward northeast with the west-dipping Jinhe——Qinghe fault zone as the nappe front.The detachment surface of the nappe structure is a gently west-dipping basement interface,which is 2—3 km deep and outcrops in the west margin of Jinhe basin.The basement depth varies generally and changes more significantly in the range from Jinhe basin to Xichang basin than in its western and eastern adjacent areas,with maximum depth being about 6 km there.The faults in the upper crust behave as the low velocity zones or velocity gradient zones,while the travel-time curves of Pg wave through the faults occur variation in negative slope and there is significant difference in the depth of basement on both sides of the faults.Faulting feature can be clearly seen on Anninghe fault,Zemuhe fault and Daliangshan fault.Anninghe fault and Zemuhe fault behave as low velocity belts,where strong concave velocity isolines appear and sharp velocity differences as compared with their two sides can be distinguished.The two faults both dip northeastward.Daliangshan fault is composed of two branches,with the west branch dipping southwestward and the east one northeastward,being characterized by rapid velocity variation structure in a narrow belt.Mopan-shan fault dips toward southwest.Heishuihe fault is divided into two branches,with west one dipping toward southwest and east one dipping toward northeast.The east edge fault of Xichang Mesozoic basin dips toward southwest.
引文
崔作舟,卢德源,陈纪平,张之英,黄立言.1987.攀西地区的深部地壳结构与构造[J].地球物理学报,30(2):566--580.
葛肖虹.1984.川西盐源推覆构造的探讨[J].长春地质学院学报,35(1):36--43.
江在森,牛安福,王敏,黎凯武,方颖,张希,张晓亮.2005.活动断裂带构造变形定量分析[J].地震学报,27(6):610--619.
阚荣举,王绍晋,黄琨,宋文.1983.中国西南地区现代构造应力场与板内断块相对运动[J].地震地质,5(2):79--90.
李坪,汪良谋.1975.云南川西地区地震地质基本特征的探讨[J].地质科学,(4):308--325.
梁尚鸿,束沛鎰,李幼铭,朱碚定,张立敏.1986.攀西地区地震分布和构造应力场特征[J].地球物理学报,29(6):557--566.
刘丽华,徐强,范明祥.2003.西昌盆地构造特征和含油气条件分析[J].天然气工业,23(5):34--38.
骆耀南.1985.中国攀枝花-西昌古裂谷带[G]∥张云湘主编.中国攀西裂谷文集(1).北京:地质出版社:1--25.
吕江宁,沈正康,王敏.2003.川滇地区现代地壳运动速度场和活动块体模型研究[J].地震地质,25(4):543--552.
孙克忠,滕吉文,金东敏,郑晔.1987.攀西构造带Q值及其横向不均匀性[J].地球物理学报,30(1):102--104.
唐若龙,杨登文,刘述前,王中伟,叶秀华,陈忠禹.1985.攀西裂谷先张后压的双重构造特征[G]∥张云湘主编.中国攀西裂谷文集(1).北京:地质出版社:71--82.
滕吉文.1987.攀枝花-西昌古裂谷与"活化"的地球物理特征[J].地球物理学报,30(6):581--593.
汪良谋.1982.康滇活动构造带的形成机制及其强震活动[G]∥中国地震学会地震地质专业委员会主编.中国活动断裂.北京:地震出版社:242--250.
王夫运,段永红,杨卓欣,张成科,赵金仁,张建狮,张先康,刘启元,朱艾斓,徐锡伟,刘宝峰.2008.川西盐源-马边地震带上地壳速度结构和活动断裂研究-高分辨率地震折射实验结果[J].中国科学:D辑,38(5):611--621.
闻学泽.2000.四川西部鲜水河-安宁河-则木河断裂带的地震破裂分段特征[J].地震地质,22(3):239--249.
熊绍柏,滕吉文,尹周勋,赖明惠,黄一平.1986.攀西构造带南部地壳与上地幔结构的爆炸地震学研究[J].地球物理学报,29(3):235--244.
徐锡伟,闻学泽,郑荣章,马文涛,宋方敏,于贵华.2003.川滇地区活动块体最新构造变动式样及其动力来源[J].中国科学:D辑,33(增刊):151--161.
易桂喜,闻学泽,范军,王思维.2004.由地震活动参数分析安宁河-则木河断裂带的现今活动习性及地震危险性[J].地震学报,26(3):294--303.
尹周勋,滕吉文,熊绍柏.1987.渡口及其邻近地区地壳浅层结构的研究[J].地球物理学报,30(2):22--30.
尹周勋,熊绍柏.1992.西昌-渡口-牟定地带二维地壳结构的爆炸地震研究[J].地球物理学报,35(4):451--458.
袁学诚.1989.论康滇地轴的深部构造[J].地质学报,63(1):1--13.
张培震,王琪,马宗晋.2002.中国大陆现今构造运动的GPS速度场和活动地块[J].地学前缘,9(2):430--440.
张培震,邓启东,张国民,马瑾,甘卫军,闵伟,毛凤英,王琪.2003.中国大陆的强震活动与活动地块[J].中国科学:D辑,33(增刊):12--20.
朱碚定,李幼铭,张立敏,束沛鎰,梁尚鸿.1986.川南、滇北地震台网区域壳幔介质分层结构的初步研究[J].地球物理学报,29(3):245--253.
Fuis G S,Okaya D A,Clayton R W,Lutter WJ,Ryberg T,Brocher T M,Henyey T L,Benthien M L,Davis P M,Mori J,Catchings R D,tenBrink US,Kohler M D,Klitgord K D,Bohannon R G.1996.Images of crust beneathsouthern California will aid study of earthquakes and their effects[J].Eos Agu,77(18):173--176.
Fuis G S,Ryberg T,Lutter WJ,Ehlig P L.2001.Seismic mapping of shallowfault zonesin the San Gabriel Mountainsfromthe Los Angeles region seismic experiment,Southern California[J].J Geophys Res,106(B4):6549--6568.
Hole J A.1992.Nonlinear high-resolution three-dimensional seismic travel time tomography[J].J Geophys Res,97(B5):6553--6562.
Scheidegger A E,Will more P L.1957.The use of a least square method for the interpretation of data fromseismic sur-veys[J].Geopysics,22(1):9--22.
Vidale J E.1990.Finite-difference calculation of travel times in three-dimensions[J].Geophysics,55(5):521--526.
Yan Z M,Robert WC,Jason S.2005.Seismic refraction evidence for steep faults cutting highly attenuated continentalbasement in the central Transverse ranges,California[J].Geophys J Int,160(2):651--666.
葛肖虹.1984.川西盐源推覆构造的探讨[J].长春地质学院学报,35(1):36--43.
江在森,牛安福,王敏,黎凯武,方颖,张希,张晓亮.2005.活动断裂带构造变形定量分析[J].地震学报,27(6):610--619.
阚荣举,王绍晋,黄琨,宋文.1983.中国西南地区现代构造应力场与板内断块相对运动[J].地震地质,5(2):79--90.
李坪,汪良谋.1975.云南川西地区地震地质基本特征的探讨[J].地质科学,(4):308--325.
梁尚鸿,束沛鎰,李幼铭,朱碚定,张立敏.1986.攀西地区地震分布和构造应力场特征[J].地球物理学报,29(6):557--566.
刘丽华,徐强,范明祥.2003.西昌盆地构造特征和含油气条件分析[J].天然气工业,23(5):34--38.
骆耀南.1985.中国攀枝花-西昌古裂谷带[G]∥张云湘主编.中国攀西裂谷文集(1).北京:地质出版社:1--25.
吕江宁,沈正康,王敏.2003.川滇地区现代地壳运动速度场和活动块体模型研究[J].地震地质,25(4):543--552.
孙克忠,滕吉文,金东敏,郑晔.1987.攀西构造带Q值及其横向不均匀性[J].地球物理学报,30(1):102--104.
唐若龙,杨登文,刘述前,王中伟,叶秀华,陈忠禹.1985.攀西裂谷先张后压的双重构造特征[G]∥张云湘主编.中国攀西裂谷文集(1).北京:地质出版社:71--82.
滕吉文.1987.攀枝花-西昌古裂谷与"活化"的地球物理特征[J].地球物理学报,30(6):581--593.
汪良谋.1982.康滇活动构造带的形成机制及其强震活动[G]∥中国地震学会地震地质专业委员会主编.中国活动断裂.北京:地震出版社:242--250.
王夫运,段永红,杨卓欣,张成科,赵金仁,张建狮,张先康,刘启元,朱艾斓,徐锡伟,刘宝峰.2008.川西盐源-马边地震带上地壳速度结构和活动断裂研究-高分辨率地震折射实验结果[J].中国科学:D辑,38(5):611--621.
闻学泽.2000.四川西部鲜水河-安宁河-则木河断裂带的地震破裂分段特征[J].地震地质,22(3):239--249.
熊绍柏,滕吉文,尹周勋,赖明惠,黄一平.1986.攀西构造带南部地壳与上地幔结构的爆炸地震学研究[J].地球物理学报,29(3):235--244.
徐锡伟,闻学泽,郑荣章,马文涛,宋方敏,于贵华.2003.川滇地区活动块体最新构造变动式样及其动力来源[J].中国科学:D辑,33(增刊):151--161.
易桂喜,闻学泽,范军,王思维.2004.由地震活动参数分析安宁河-则木河断裂带的现今活动习性及地震危险性[J].地震学报,26(3):294--303.
尹周勋,滕吉文,熊绍柏.1987.渡口及其邻近地区地壳浅层结构的研究[J].地球物理学报,30(2):22--30.
尹周勋,熊绍柏.1992.西昌-渡口-牟定地带二维地壳结构的爆炸地震研究[J].地球物理学报,35(4):451--458.
袁学诚.1989.论康滇地轴的深部构造[J].地质学报,63(1):1--13.
张培震,王琪,马宗晋.2002.中国大陆现今构造运动的GPS速度场和活动地块[J].地学前缘,9(2):430--440.
张培震,邓启东,张国民,马瑾,甘卫军,闵伟,毛凤英,王琪.2003.中国大陆的强震活动与活动地块[J].中国科学:D辑,33(增刊):12--20.
朱碚定,李幼铭,张立敏,束沛鎰,梁尚鸿.1986.川南、滇北地震台网区域壳幔介质分层结构的初步研究[J].地球物理学报,29(3):245--253.
Fuis G S,Okaya D A,Clayton R W,Lutter WJ,Ryberg T,Brocher T M,Henyey T L,Benthien M L,Davis P M,Mori J,Catchings R D,tenBrink US,Kohler M D,Klitgord K D,Bohannon R G.1996.Images of crust beneathsouthern California will aid study of earthquakes and their effects[J].Eos Agu,77(18):173--176.
Fuis G S,Ryberg T,Lutter WJ,Ehlig P L.2001.Seismic mapping of shallowfault zonesin the San Gabriel Mountainsfromthe Los Angeles region seismic experiment,Southern California[J].J Geophys Res,106(B4):6549--6568.
Hole J A.1992.Nonlinear high-resolution three-dimensional seismic travel time tomography[J].J Geophys Res,97(B5):6553--6562.
Scheidegger A E,Will more P L.1957.The use of a least square method for the interpretation of data fromseismic sur-veys[J].Geopysics,22(1):9--22.
Vidale J E.1990.Finite-difference calculation of travel times in three-dimensions[J].Geophysics,55(5):521--526.
Yan Z M,Robert WC,Jason S.2005.Seismic refraction evidence for steep faults cutting highly attenuated continentalbasement in the central Transverse ranges,California[J].Geophys J Int,160(2):651--666.
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