利用接收函数反演龙门山断裂带及邻区深部结构
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摘要
利用接收函数的方法通过接收震中距30°～90°、震级在5.5以上的远震事件反演龙门山断裂带及其邻区的深部结构,探索汶川地震形成原因。结果表明,扬子地台西缘的莫霍面向西侧倾斜缓降;处在龙门山推覆体范围之内的都江堰、汶川一带莫霍面起伏变化不大,在跨过龙门山中央断裂带后开始下降,向北降至黑水县附近后平缓上升。结合2005年10月至2007年4月远震P波波形资料接收函数反演结果:①2条被动源剖面均显示莫霍面在龙门山推覆体中央位置深度约43km的地方出现不同程度的陡降,说明该断裂带是地壳厚度的陡变带,为扬子地台和松潘甘孜地台的构造边界。②莫霍面深度向南陡降至最深约68km处后平缓上升,向北陡降至最深约58km处后平缓上升。表明松潘-甘孜地块东缘地壳厚度呈南深北浅、东深西浅分布。
From September 2009 to April 2011,18 broadband seismographs are placed in a profile acrossing Chengdu,Ziyang,Wenchuan,Heishui,Hongyuan and Maqu.The profile is about 500 km long.With the addition of 7 seismic stations which belong to the Sichuan provincial seismological bureau,the epicentral distance in 30°~90° and the magnitude greater than 5.5 level,261 earthquake events are selected to invert the deep structure of the Longmenshan fault zone and adjacent areas by the received function.The results of the study show that on the west margin of Yangtz platform,the Moho tilts to the west slowly,the depth changes from the 35 km to 45km,while near Dujiangyan and Wenchuan,the depth changes little.After crossing the Longmenshan central fault the Moho starts to drop,until Heishui(58 km) it begins to rise slowly.Compared with the inversion results in 2007,the following conclusions can be arrived: 1) Two profiles both show that the steep descent appears in the center of the Longmenshan nappe.It illustrates that the fault zone is the place where the crust has a sudden change.2) To the south,the depth of the Moho tilts down 68 km,then rises,but to the north,the depth of the Moho tilts down 58 km,then rises.So this paper considers that on the eastern margin of the Songpan-Ganzi massif,the thickness of the crust shows that the south is thick and the north thin and the east is thick and the west thin.
From September 2009 to April 2011,18 broadband seismographs are placed in a profile acrossing Chengdu,Ziyang,Wenchuan,Heishui,Hongyuan and Maqu.The profile is about 500 km long.With the addition of 7 seismic stations which belong to the Sichuan provincial seismological bureau,the epicentral distance in 30°~90° and the magnitude greater than 5.5 level,261 earthquake events are selected to invert the deep structure of the Longmenshan fault zone and adjacent areas by the received function.The results of the study show that on the west margin of Yangtz platform,the Moho tilts to the west slowly,the depth changes from the 35 km to 45km,while near Dujiangyan and Wenchuan,the depth changes little.After crossing the Longmenshan central fault the Moho starts to drop,until Heishui(58 km) it begins to rise slowly.Compared with the inversion results in 2007,the following conclusions can be arrived: 1) Two profiles both show that the steep descent appears in the center of the Longmenshan nappe.It illustrates that the fault zone is the place where the crust has a sudden change.2) To the south,the depth of the Moho tilts down 68 km,then rises,but to the north,the depth of the Moho tilts down 58 km,then rises.So this paper considers that on the eastern margin of the Songpan-Ganzi massif,the thickness of the crust shows that the south is thick and the north thin and the east is thick and the west thin.
引文
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[9]袁丽文,郑斯华.用远震接收函数反演福建地区宽频带台站下方莫霍界面深度[J].华南地震,2009,29(3):85-95.
[10]徐强,赵俊猛.接收函数方法的研究综述[J].地球物理学进展,2008,23(6):1708-1714.
[11]嘉世旭,张先康,赵金仁,等.若尔盖盆地及周缘褶皱造山带地壳结构深地震测深结果[J].中国科学:D辑,2009,39(9):1200-1208.
[12]李志伟,胥颐,黄润秋,等.龙门山地区的P波速度结构与汶川地震的深部构造特征[J].中国科学:D辑,2011,41(3):283-290.
[13]杨中书,崇加军,倪四道,等.若利用远震接收函数研究江西省地震台站下方莫霍面深度及泊松比分布[J].华南地震,2010,30(1):47-55.
[14]刘启元,李昱,陈九辉,等.汶川Ms 8.0级地震:地壳上地幔速度结构初步研究[J].地球物理学报,2009,52(2):309-319.
[15]朱迎堂,王绪本,余年,等.龙门山大地电磁深部结构及汶川级地震(Ms 8.0)[J].地质学报,2008,82(12):1770-1777.
[2]张培震,闻学泽,徐锡伟,等.2008年汶川8.0级特大地震孕育和发生的多单元组合模式[J].科学通报,2009,54(7):944-953.
[3]楼海,王椿镛,吕智勇,等.2008年汶川Ms 8.0级地震的深部构造环境远震P波接收函数和布格重力异常的联合解释[J].中国科学:D辑,2008,38(10):1207-1220.
[4]贾丽华,崇加军,刘渊源,等.利用远震接收函数研究辽宁地区地壳厚度及泊松比[J].地震地质,2010,32(2):260-265.
[5]贺传松,王椿镛,吴建平.用远震接收函数研究滇西地区的深部结构[J].地震学报,2004,26(3):238-246.
[6]吴庆举,曾融生.用宽频带远震接收函数研究青藏高原的地壳结构[J].地球物理学报,1998,41(5):669-676.
[7]齐少华,刘启元,陈九辉,等.汶川Ms 8.0级地震:龙门山断裂两侧地壳各向异性的初步研究[J].地震地质,2009,31(3):377-384.
[8]朱介寿.汶川地震的岩石圈深部结构与动力学背景[J].成都理工大学学报:自然科学版,2008,35(4):348-356.
[9]袁丽文,郑斯华.用远震接收函数反演福建地区宽频带台站下方莫霍界面深度[J].华南地震,2009,29(3):85-95.
[10]徐强,赵俊猛.接收函数方法的研究综述[J].地球物理学进展,2008,23(6):1708-1714.
[11]嘉世旭,张先康,赵金仁,等.若尔盖盆地及周缘褶皱造山带地壳结构深地震测深结果[J].中国科学:D辑,2009,39(9):1200-1208.
[12]李志伟,胥颐,黄润秋,等.龙门山地区的P波速度结构与汶川地震的深部构造特征[J].中国科学:D辑,2011,41(3):283-290.
[13]杨中书,崇加军,倪四道,等.若利用远震接收函数研究江西省地震台站下方莫霍面深度及泊松比分布[J].华南地震,2010,30(1):47-55.
[14]刘启元,李昱,陈九辉,等.汶川Ms 8.0级地震:地壳上地幔速度结构初步研究[J].地球物理学报,2009,52(2):309-319.
[15]朱迎堂,王绪本,余年,等.龙门山大地电磁深部结构及汶川级地震(Ms 8.0)[J].地质学报,2008,82(12):1770-1777.
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