云南地区上部地壳结构和地震构造环境的层析成像研究
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摘要
利用4条DSS丰富的测深资料,对云南地区上部地壳结构和地震构造环境进行了层析成像研究。成像结果显示,得到的速度模型与地表盆地、隆起与断裂有很好的对应关系,显示了与地表火山岩系相应的低速异常体,云南地区上部地壳横向不均匀性显著,结晶基底的深度一般为0～5km,局部基底高于海平面,基岩直接出露地表,同时在一些大的坳陷处沉积厚度可达8～12km。作为一级构造单元的昌宁-双江断裂可能切割不深,而红河断裂作为“板块缝合线”切割较深,有延伸到中下地壳的迹象。云南地区历史上的广泛的火山活动与现今中强地震的发生有紧密联系,有的地方尽管现今地表已不再有火山活动,但中下地壳活动并未停止,存在较大的应力作用,由于地表火山活动停止,来自中下地壳和上地幔的大部分能量得不到释放,而在有利的构造部位积聚,以及盆地水的渗透、其它流体的作用和外动力作用,可能是云南地区经常诱发中强地震的重要原因。
Investigation has been made for the upper crust structure and seismotectonic environments in Yunnan Province by using the plentiful DSS data of the four profiles. The derived velocity model has a good relationship with the exposed basins, uplifts and faults, and the low velocities anomaly corresponding to the volcanoes also has been revealed. There exits a prominent lateral inhomogeneity within the upper crust of Yunnan region. The depth of crystalline basement generally ranges from 0 km to 5 km, and the bedrock are exposed on the ground directly in some places, nevertheless the thickness of sedimentary cover also can reach to 8 km or even 12 km at some large depressions. Although the Changning-Shuangjiang fault is a boundary between two first class tectonic units, its incision depth within the crust however maybe shallow. On the other hand, known as the plates' seam, the Honghe fault has a distinct evidence of extending into the mid-lower crust. The widely spread activity of the volcanoes in the geological era has a closed relationship with the earthquake's occurrence up-to-date. Despite of the stop of the volcanoes in some places on the ground, the material in the mid-lower crust is still active, and there still exists strong upward stress. For the ceasing of the volcanoes on the surface, most parts of the power from the lower crust and upper mantle cannot be released, therefore it accumulates at some beneficial tectonic locations. Moreover, saturation of the water from the basin and the action of other fluids, and the affection of outer stress maybe another direct reason account for the strong earthquakes' occurrence in Yunnan region.
Investigation has been made for the upper crust structure and seismotectonic environments in Yunnan Province by using the plentiful DSS data of the four profiles. The derived velocity model has a good relationship with the exposed basins, uplifts and faults, and the low velocities anomaly corresponding to the volcanoes also has been revealed. There exits a prominent lateral inhomogeneity within the upper crust of Yunnan region. The depth of crystalline basement generally ranges from 0 km to 5 km, and the bedrock are exposed on the ground directly in some places, nevertheless the thickness of sedimentary cover also can reach to 8 km or even 12 km at some large depressions. Although the Changning-Shuangjiang fault is a boundary between two first class tectonic units, its incision depth within the crust however maybe shallow. On the other hand, known as the plates' seam, the Honghe fault has a distinct evidence of extending into the mid-lower crust. The widely spread activity of the volcanoes in the geological era has a closed relationship with the earthquake's occurrence up-to-date. Despite of the stop of the volcanoes in some places on the ground, the material in the mid-lower crust is still active, and there still exists strong upward stress. For the ceasing of the volcanoes on the surface, most parts of the power from the lower crust and upper mantle cannot be released, therefore it accumulates at some beneficial tectonic locations. Moreover, saturation of the water from the basin and the action of other fluids, and the affection of outer stress maybe another direct reason account for the strong earthquakes' occurrence in Yunnan region.
引文
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陈天培,秦德厚,韩文华,等.1969． 中华人民共和国区域地质调查报告.1:20万,建水幅[R].云南省地质局,119
陈学波,李金森,赵静娴,等.1994． 三江构造带基底构造特征与强震活动关系[A].见:陈运泰,阐荣举,滕古文,等主编.中国固体地球物理学进展[C].北京:海洋出版社,41～54
胡鸿翔,高世玉.1993． 云南地区地壳浅部基底速度细结构的研究[J].中国地震,19(4) :356～363
胡鸿翔,李学清.1994． 云南地区孟连-思茅-马龙剖面的基底速度细结构[A].见:陈运泰,阚荣举,滕吉文,等主编.中国固体地球物理学进展[C].北京:海洋出版社,100～106
胡鸿翔,陆涵行,王椿镛,等.1986． 云南地区地壳结构的爆破地震研究[J].地球物理学报,29(2) :133～144
阚荣举,林中洋.1986． 云南地壳上地幔构造的初步研究[J].中国地震,2(4) :50～61
阚荣举,赵晋明.1994． 腾冲火山地区的壳幔构造[A].见:陈运泰,阚荣举,滕吉文,等主编.中国固体地球物理学进展[C].北京:海洋出版社,23～30
林中洋,胡鸿翔,张文彬,等.1993． 云南地区地壳上地幔速度结构特征的研究[J].地震学报,15(4) :427～440
马杏垣主编.1989． 中国岩石圈动力学图集[M].北京:中国地图出版社,51
王椿镛,Mooney W D,王溪莉,等.2002a.川滇地区地壳L地幔三维速度结构研究[J].地震学报,24(1) :1～16
王椿镛,楼海,吴建平,等.2002b.腾冲火山地热区地壳结构的地震学研究[J].地震学报,24(3) :231～242
王椿镛,张先康,丁志峰,等.1997． 大别造山带上部地壳结构的有限差分层析成像[J].地球物理学报,40(4) :496～501
Ammon C J, Vidale J E. 1993． Tomography without rays[J]. Bull Seism Soc Amer, 83: 509 ～ 528
Hole J A. 1992． Nonlinear high-resolution three-dimentional seismic travel time tomography[J]. J Geophys Res, 97:6553～6562
Vidale J E. 1988． Finite-difference traveltime calculation[J]. Bull Seism Soc Amer, 78: 2062～2076
Vidale J E. 1990． Finite difference calculation of traveltimes in three dimentions[J]. Geophysics, 55: 521 ～ 526
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