利用地震层析成像数据修正中国西北地区莫霍界面深度
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摘要
考虑到地壳和上地幔密度异常对地表重力的影响,本文提出了修正单纯利用重力资料 反演地壳厚度的算法．该算法利用地震层析成像结果推算出地壳和上地幔密度异常分布,然 后计算由此分布引起的地表重力异常,再从观测布格重力异常中扣除上述密度异常引起的重 力效应,最后在地壳均衡假设的基础上顾及到对反演参考深度的修正,直接反演区域地壳厚 度．本文利用胥颐等地震层析成像的数据,修正了中国西北地区莫霍界面的深度．结果表明, 该区域地壳和上地幔密度异常引起的地表重力异常值为—60×1O-5m／s2～30×10-5m／s2． 与直接使用布格重力异常反演地壳厚度相比较,该密度异常对该区域莫霍界面将产生约6 km 的修正．本方法使得利用重力数据反演地壳厚度在理论上更为完备,实际应用中也比较可 行,为更进一步逼近莫霍界面的真实形态提供了一种途径．
Considering the influence of the density anomaly of the crust and upper mantle on the gravity, this paper provides a new arithmetic to inverse the crustal thickness. Applying the result of seismologic tomography, we calculate the lateral density heterogeneity of the crust and upper mantle and the gravity anomalies resulted from such lateral density heterogeneity, and then subtract gravity anomalies caused by mentioned density anomalies from observed Bouguer anomalies. Finally in view of the correction to the initial crustal thickness grounded on the hypothesis of isostasy, inverse the regional crustal thickness. Using the data of seismic tomography offered by Xu Yi et al, we inverse the Moho depth beneath northwestern China and obtain the gravity anomalies on the surface of the earth is - 60×10-5 m/s2-30×105 m/s2. Compared with the result inversed directly using Bouguer anomalies, this method can bring correction of 6 km to the Moho depth. And when we inverse the thickness of the crust using the data of gravity, it will be further mature in theory, be feasible in practice and provide a new arithmetic for us to understand the conformation of the Moho.
Considering the influence of the density anomaly of the crust and upper mantle on the gravity, this paper provides a new arithmetic to inverse the crustal thickness. Applying the result of seismologic tomography, we calculate the lateral density heterogeneity of the crust and upper mantle and the gravity anomalies resulted from such lateral density heterogeneity, and then subtract gravity anomalies caused by mentioned density anomalies from observed Bouguer anomalies. Finally in view of the correction to the initial crustal thickness grounded on the hypothesis of isostasy, inverse the regional crustal thickness. Using the data of seismic tomography offered by Xu Yi et al, we inverse the Moho depth beneath northwestern China and obtain the gravity anomalies on the surface of the earth is - 60×10-5 m/s2-30×105 m/s2. Compared with the result inversed directly using Bouguer anomalies, this method can bring correction of 6 km to the Moho depth. And when we inverse the thickness of the crust using the data of gravity, it will be further mature in theory, be feasible in practice and provide a new arithmetic for us to understand the conformation of the Moho.
引文
方剑．1999．利用卫星重力资料反演地壳及岩石圈厚度[J]．地壳形变与地震．19(1):26～31
黄建平,傅容珊,许萍,等．2006．利用布格重力异常和地形数据反演中国地区的地壳厚度[J]．地震学报(待发表)．
李秋声,卢德源,高锐,等．2000．横跨西昆仑—塔里木接触带的爆炸地震测深[J]．中围科学,D辑．30(增刊):16～21
刘元龙,郑建昌,武传珍．1987．利用重力资料反演三维密度界面的值面系数法[J]．地球物理学报．30(2):186～196
卢德源,李秋声,高锐,等．2000．横跨天山的人工爆炸地震剖面[J]．科学通报,45(9):982～988
盂万辉．1996．关于地壳厚度计算方法的修正[J]．内陆地震．10(3):25l～256
腾吉文,曾融生,闫雅芬,等．2002．东亚大陆及周边海域Moho界面深度分布和基本构造格局[J]．中国科学,D辑,32 (2):89～100
胥颐,刘福田,刘建华,等．2000．中国大陆西北造山带及其毗邻盆地的地震层析成像[J]．中国科学．D辑,30(2):113 ～123
徐佩芬,刘福田,王清晨,等．2000．大别—苏鲁碰撞造山带的地震层析成像研究——岩石圈三维速度结构[J]．地球物 理学报,43(3):377～386
殷秀华,史志宏,刘占坡．1989．地壳厚度(重力反演)[A]．见:马杏垣主编．中国岩石圈动力学地图集[C]．北京:中国 地图出版社,12
Masters G, Jordan T H, Silver P G, et al. 1982. A spherical earth structure from fundamental sphencal-mode data[J]. Nature, 298: 609-613
Su W J, Woodward R L, Dzeiwonski A M, 1994. Degree 12 model of shear velocity heterogenity m the mantle [J]. J Geophys Res, 99: 6 945-6 980
Xu Yi, Liu Futian, Liu Jianhua. et al. 2002. Crust and upper mantle structure beneath western China from P wave travel time tomography[J], J Geophys Res, 107(B10): 2 220-2 234
黄建平,傅容珊,许萍,等．2006．利用布格重力异常和地形数据反演中国地区的地壳厚度[J]．地震学报(待发表)．
李秋声,卢德源,高锐,等．2000．横跨西昆仑—塔里木接触带的爆炸地震测深[J]．中围科学,D辑．30(增刊):16～21
刘元龙,郑建昌,武传珍．1987．利用重力资料反演三维密度界面的值面系数法[J]．地球物理学报．30(2):186～196
卢德源,李秋声,高锐,等．2000．横跨天山的人工爆炸地震剖面[J]．科学通报,45(9):982～988
盂万辉．1996．关于地壳厚度计算方法的修正[J]．内陆地震．10(3):25l～256
腾吉文,曾融生,闫雅芬,等．2002．东亚大陆及周边海域Moho界面深度分布和基本构造格局[J]．中国科学,D辑,32 (2):89～100
胥颐,刘福田,刘建华,等．2000．中国大陆西北造山带及其毗邻盆地的地震层析成像[J]．中国科学．D辑,30(2):113 ～123
徐佩芬,刘福田,王清晨,等．2000．大别—苏鲁碰撞造山带的地震层析成像研究——岩石圈三维速度结构[J]．地球物 理学报,43(3):377～386
殷秀华,史志宏,刘占坡．1989．地壳厚度(重力反演)[A]．见:马杏垣主编．中国岩石圈动力学地图集[C]．北京:中国 地图出版社,12
Masters G, Jordan T H, Silver P G, et al. 1982. A spherical earth structure from fundamental sphencal-mode data[J]. Nature, 298: 609-613
Su W J, Woodward R L, Dzeiwonski A M, 1994. Degree 12 model of shear velocity heterogenity m the mantle [J]. J Geophys Res, 99: 6 945-6 980
Xu Yi, Liu Futian, Liu Jianhua. et al. 2002. Crust and upper mantle structure beneath western China from P wave travel time tomography[J], J Geophys Res, 107(B10): 2 220-2 234
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