川滇地区莫霍面深度和地壳厚度

引用本文

徐志萍, 王夫运, 姜磊, 徐顺强, 唐淋. 川滇地区莫霍面深度和地壳厚度[J]. 地震地质, 2018,40(6): 1318-1331.
XU Zhi-ping, WANG Fu-yun, JIANG Lei, XU Shun-qiang, TANG Lin. THE DEPTH OF MOHO INTERFACE AND CRUSTAL THICKNESS IN SICHUAN-YUNNAN REGION, CHINA[J]. SEISMOLOGY AND GEOLOGY, 2018,40(6): 1318-1331. 复制到剪切板

DOI:10.3969/j.issn.0253-4967.2018.06.009
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川滇地区莫霍面深度和地壳厚度

徐志萍¹⁾, 王夫运^1),^*, 姜磊¹⁾, 徐顺强¹⁾, 唐淋²⁾

1)中国地震局地球物理勘探中心, 郑州 450002

2)四川省地震局, 成都 610041

*通讯作者: 王夫运, 男, 研究员, 从事深地震测深综合研究工作, E-mail:fuyunwang@x263.ent。

〔作者简介〕徐志萍, 女, 1987年生, 2012年于中国地质大学(武汉)获地球探测与信息技术专业硕士学位, 工程师, 主要研究方向为重磁电方法与深部结构构造, 电话: 0371-63757378, E-mail: xuzhipingcom@126.com。

收稿日期: 2018-04-20

基金项目: 国家自然科学基金(41774072)和川滇国家地震监测预报实验场项目(2016CESE0103)共同资助

摘要

利用滑动平均法从川滇地区布格重力异常场分离出主要反映莫霍面起伏的低频布格重力异常场, 将地震模型转换、并经过高程改正的密度模型作为初始模型, 根据不同构造单元之间莫霍面上、下密度差不同, 采用Parker法对低频布格重力异常场进行分区反演, 得到了该区莫霍面深度和地壳厚度分布。结果显示: 研究区西北部青藏块体从边缘向内部莫霍面深度和地壳厚度加深和增厚, 分别为52~62km和54~66km; 四川盆地莫霍面深度为38~42km; 从南东向北西川滇菱形块体莫霍面深度为42~62km; 红河断裂带以西的滇西地块, 从南向北莫霍面深度为34~52km; 龙门山、红河断裂带是莫霍面深度变化的梯度带; 红河断裂带两侧自北向南莫霍面深度差异逐渐增加; 攀枝花裂谷下方的莫霍面未发现明显隆起。川滇地区莫霍面深度分布明显受印度板块与欧亚板块碰撞及其向中南半岛侧向俯冲的制约。文中采用分区反演得到的莫霍面深度模型与已有的人工地震探测结果之间的均方差<1.7km, 同时通过与整体反演结果对比, 表明在不同构造单元的地壳速度、密度结构存在明显差异的区域, 以高分辨地震探测结果为约束, 开展分区密度界面反演工作, 可有效提高反演结果的可靠性。

关键词: 布格重力异常; 川滇地区; 分区密度界面反演; 莫霍面深度

中图分类号:P315.72⁺6 文献标志码:A 文章编号:0253-4967(2018)06-1318-14

THE DEPTH OF MOHO INTERFACE AND CRUSTAL THICKNESS IN SICHUAN-YUNNAN REGION, CHINA

XU Zhi-ping¹⁾, WANG Fu-yun¹⁾, JIANG Lei¹⁾, XU Shun-qiang¹⁾, TANG Lin²⁾

1)Geophysical Exploration Center, China Earthquake Administration, Zhengzhou 450002, China

2)Sichuan Earthquake Agency, Chengdu 610041, China

Abstract

By using moving average method to separate Bouguer gravity anomaly field in Sichuan-Yunnan region, we got the low-frequency Bouguer gravity anomaly field which reflects the undulating of Moho interface. The initial model is obtained after seismic model transformation and elevation correction. Then, we used Parker method to invert the low-frequency Bouguer gravity anomaly field to obtain the depth of Moho interface and crustal thickness in the area. The results show that the Qinghai-Tibet block in the northwest of the study area deepens and thickens from the edge to the interior, with the depth of Moho interface and the crust thickness of about 52~62km and 54~66km, respectively. The depth of Moho interface in Sichuan Basin is about 38~42km. In Sichuan-Yunnan block, the depth of Moho interface is about 42~62km from southeast to northwest. Beneath the West Yunnan block, west of the Red River fault zone, the Moho depth is about 34~52km from south to north. The Longmen Mountains and Red River fault zone are the gradient zone of the Moho depth change. Along the Red River fault zone, the depth difference of Moho interface is increasing gradually from north to south. No obvious uplift is found on the Moho interface of Panzhihua rift valley. The depth of Moho interface distribution in Sichuan and Yunnan is obviously restricted by the collision between the Indian plate and the Eurasian plate and the lateral subduction of the Indo-China peninsula. The mean square error of the depth of Moho interface is less than 1.7km between the result of divisional density interface inversion and artificial seismic exploration. At the same time, we compared the integral with divisional inversion result. It shows that: in areas where there is obvious difference between the crust velocity and density structure in different tectonic blocks, the use of high resolution seismic exploration data as the constraints to the divisional density interface inversion can effectively improve the reliability of inversion results.

Keyword: Bouguer gravity anomalies; Sichuan-Yunnan region; divisional density interface inversion; the depth of Moho interface

文章图片

0 引言

受自45Ma以来印度板块与欧亚板块碰撞的影响, 川滇地区发生了强烈的构造变形, 西北部隆升为青藏高原的一部分, 地壳显著增厚; 西南部为一系列近NW向的大型走滑断裂所分割, 分布着走向相同的著名的横断山脉; 北部在川西高原和四川盆地之间横亘着高耸的龙门山逆冲推覆造山带。川滇地区主要的块体有川滇菱形块体、松潘-甘孜地块、扬子地块、滇西地块和华南地块(图1)。

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	图1 川滇地区地形及构造简图(据钟锴等, 2005)Fig. 1 Simplified topographic and geotectonic map of Sichuan-Yunnan region(ZHONG Kai et al., 2005).

目前, 针对川滇地区虽然开展了大量的研究工作, 但仍有一些问题尚未解决: 1)印度板块和欧亚板块碰撞引起的压缩变形导致青藏高原地壳增厚, 达到60~70km, 关于其隆升和增厚机制尚存争议, 国际上主要有 “ 大陆逃逸” 模型(Tapponnier et al., 1982)、连续变形模型(England et al., 1986)和下地壳流模式(Royden et al., 1997)等假说; 2)攀西裂谷带下方莫霍面是否隆升?隆升规模有多大?不同地球物理结果存在差异(崔作舟等, 1987; 钟锴等, 2005; 石磊等, 2015; 张恩会等, 2015); 3)在云南中南部地区通过地震剖面得到的莫霍面深度约32~40km(张恩会等, 2013; 王夫运等, 2014; 王帅军等, 2015a), 而重力反演结果多为40~45km(冯锐, 1985; 路晓翠, 2008; 张恩会等, 2015)。莫霍面作为地壳和地幔的重要分界面, 获得其可靠的深度模型对解决以上问题具有重要意义。

自20世纪80年代以来, 众学者在川滇地区布设了多条人工深地震探测剖面(熊绍柏等, 1986; 崔作舟等, 1987; 王椿镛等, 2003a, 2003b; 白志明等, 2004; 张忠杰等, 2005; 张智等, 2007; 嘉世旭等, 2014; 王夫运等, 2014; 王帅军等, 2015a, 2015b; 徐涛等, 2015), 获得了剖面下精细的地壳上地幔二维速度结构、莫霍面深度及地壳厚度。此外, 为获得川滇地区莫霍面深度的区域变化特征, 一些学者还利用重力资料来反演莫霍面深度(冯锐, 1985; 路晓翠, 2008; 姜永涛等, 2015; 张恩会等, 2015)。通过人工地震探测获得的莫霍面深度更加准确, 但覆盖范围小, 仅反映测线下方莫霍面深度的变化特征; 重力虽然横向范围大, 但其反演结果往往受初始模型和反演参数制约。因此, 本文拟将地震方法获得的地壳模型通过大地水准面校正, 变为适合重力数据反演的重力地壳模型, 给出更加合理的反演参数, 得到包含地震数据和重力数据信息的更加可靠的莫霍面深度和地壳厚度结果。

1 数据

本文收集的川滇地区布格重力异常资料来自全国地质资料馆, 该资料包含多个比例尺的数据, 有 1:10万、 1:20万、 1:50万和 1:100万, 经重采样、插值处理后得到相当于 1:50万平面布格重力异常数据。使用WGS84坐标系。资料范围为97° ~107° E, 22° ~33° N。

重力解释通常把布格重力异常看作由区域异常和局部异常组成, 区域异常幅值较大, 异常范围较宽, 具有 “ 低频” 特征, 主要是由地壳下界面(莫霍面)起伏而在横向上相对上地幔质量的巨大亏损(山区)或盈余(海洋)引起的重力异常; 局部异常一般由范围较小的构造、矿体或岩体引起的范围和幅度较小的异常, 梯度相对较大, 具有 “ 高频” 特征。因此, 在进行莫霍面反演之前, 可以利用不同场源引起重力异常的频率不同对其进行分离, 得到莫霍面起伏引起的重力异常场。本文采用滑动平均法得到了川滇地区布格重力异常区域场和局部场, 其中区域场变化特征与楼海等(2005)和路晓翠(2008)获得的结果基本一致。

图2是采用滑动平均法得到的川滇地区布格重力异常分离结果。区域重力异常(图2a)幅值较大, 在-480× 10^-5~-80× 10^-5m/s²之间, 整体呈西低东高的分布特征。在研究区西北部的青藏高原东北缘地区为低重力异常区, 四川盆地为高重力异常区, 二者之间存在一明显的重力异常梯度带, 龙门山断裂带就位于该梯度带内; 研究区南部的云南地区重力异常变化平缓, 等值线向SE方向弯曲。局部重力异常(图2b)幅值较小, 在-70× 10^-5~60× 10^-5m/s²之间, 等值线圈闭范围小, 形成局部高、低重力异常特征, 在成都地块为高重力异常特征, 龙门山断裂带西侧的3个NE向高重力异常圈闭与川西彭灌杂岩的位置相对应, 攀枝花附近的高重力异常区与峨眉大火成岩省攀枝花岩体相对应。

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	图2 川滇地区布格重力异常场源分离滑动平均结果窗口大小为250km× 275km。 a 区域场(红色矩形框内是分区反演范围); b 局部场Fig. 2 The results of source separation of Bouguer gravity anomaly in Sichuan-Yunnan region by the moving average method.

2 反演

在重力界面反演方法中, 基于频率域的Parker迭代界面反演方法(Oldenburg, 1974), 由于适应性强、计算速度快, 得到了广泛的应用。

设界面的平均深度为H, 而h是界面相对于平均深度H的距离, 设Z坐标轴向下为正, 则H以上的h为负。该起伏界面的重力异常的频谱为

$Δ \tilde{g} (u, v) = - 2 πG σ [e^{- Hs} \overset{\infty}{\sum_{n = 1}} \frac{{(- s)}^{n - 1}}{n!} {\tilde{h}}^{n}] (1)$

式(1)中, e为自然常数, σ 为密度, $s = (u^{2} + v^{2})^{1 / 2},$ G为万有引力常数, $\tilde{h}$ 为 $h$ 的频谱, $Δ \tilde{g}$ 为重力异常 $Δ g$ 的频谱, $Δ {\tilde{Z}}_{a}$ 为垂直磁异常 $Δ Z_{a}$ 的频谱等。式(1)是重力界面正演计算式, 稍作变化即可作为反演迭代式, 具体表达为:

$\tilde{h}_{(i + 1)} = \frac{e^{Hs}}{- 2 πG σ} Δ \tilde{g} + \overset{\infty}{\sum_{n = 2}} ({\tilde{h}}_{(i)}^{n}) \cdot \frac{{(- s)}^{n - 1}}{n!} (2)$

其中h₍_i₎、 h₍_i₊₁₎分别为第i次和第i+1次界面起伏的近似值。该算法每次迭代得到的是h值而非其修正量, 因而存在不宜收敛的缺点。为克服这一缺点, 本文在进行莫霍面反演时采用了GMS4.0软件(中国地质大学(武汉))中3D帕克法密度界面反演程序, 该程序取迭代方法如下:

(1)取式(2)的一级近似值, 得到h的一级近似值h₍₁₎的频谱 ${\tilde{h}}_{(1)} : {\tilde{h}}_{(1)} = \frac{e^{Hs}}{- 2 πG σ} Δ \tilde{g};$

(2)把一级近似h₍₁₎代入式(1)得到: $Δ {\tilde{g}}_{(1)} = - 2 πG σ [e^{- Hs} \overset{\infty}{\sum_{n = 1}} \frac{{(- s)}^{n - 1}}{n!} {\tilde{h}}_{(1)}^{n}];$

(3)根据 $Δ {\tilde{g}}_{(1)}$ 求 ${\tilde{h}}_{(2)} : {\tilde{h}}_{(2)} = \frac{e^{Hs}}{- 2 πG σ} [Δ \tilde{g} - Δ {\tilde{g}}_{(1)}];$

(4)把 ${\tilde{h}}_{(2)}$ 进行反变换得到h₍₂₎, h的二级近似值就等于h₍₁₎+h₍₂₎, 将其代入式(1)得到 $Δ \tilde{g}$ 的二级近似 $Δ {\tilde{g}}_{(2)};$

(5)根据方程式 ${\tilde{h}}_{(3)} = \frac{e^{Hs}}{- 2 πG σ} [Δ \tilde{g} - Δ {\tilde{g}}_{(2)}] 得到 {\tilde{h}}_{(3)};$

把 ${\tilde{h}}_{(3)}$ 进行反变换得到h₍₃₎, 则h的三级近似值为h₍₁₎+h₍₂₎+h₍₃₎, 再继续求取Δ ${\tilde{g}}_{(3)}$ , …, 直到h的第n级近似值与第n-1次近似值之差满足精度为止, 界面深度h为h= $\overset{n}{\sum_{i = 1}}$ h_(i)。

GMS4.0软件在反演时要求将反演界面的平均深度、界面密度差以及变密度因子作为已知条件输入, 即采用密度随深度呈指数变化( $Δ ρ (z) = Δ ρ_{0} e^{- μz}, 其中, Δ ρ 为密度差, μ$ 为变密度因子, $z$ 为深度)的变密度模型进行莫霍面反演, 同时为消除边界效应的影响, 在反演时对观测数据以2的n次幂进行扩展, 反演点数> 实际点数, 当界面深度h的第n级近似值与第n-1次近似值之差< 10^-5, 终止迭代。

根据人工地震探测结果得到川滇地区不同构造单元下地壳和上地幔P波速度, 并利用速度-密度转换公式 $V_{P} = 0.002 i 8 ρ - 1.575 i 2$ 计算莫霍界面上、下密度差(Christensen et al., 2003), 作为反演密度差(表1)。在青藏高原东北缘的松潘-甘孜地块莫霍面深度约50~60km, 四川盆地地壳厚度约40~45km(嘉世旭等, 2014; 王帅军等, 2015b), 云南地区地壳厚度在红河断裂两侧变化较大(张恩会等, 2013; 王夫运等, 2014; 王帅军等, 2015a), 该断裂带以西, 莫霍面深度和密度差均小于断裂带以东, 且该断裂可能深切至莫霍面(王椿镛等, 2002; 周光全等, 2003; 施发奇等, 2012)。基于以上考虑, 在进行莫霍面反演时先对整个区域进行反演, 选用平均深度46km、密度差0.4g/cm³、变密度因子0.01g/cm³, 然后再对包含红河断裂区域(图1a中红色矩形框所包含区域)进行单独反演, 选用平均深度42km、密度差0.33g/cm³、变密度因子0.001g/cm³, 最后对反演结果以红河断裂带为界进行数据拼接, 得到川滇地区莫霍面深度。

表1 川滇地区地壳平均速度、密度差 Table1 Average crustal velocity and density difference in Sichuan-Yunnan region

3 莫霍面深度及地壳厚度

3.1 莫霍面深度

图3a是川滇地区莫霍面整体反演结果, 该结果与前人采用重力反演得到的莫霍面深度具有较好的一致性(冯锐, 1985; 路晓翠, 2008; 姜永涛等, 2015; 张恩会等, 2015), 在滇西地块内莫霍面自北向南逐渐变浅, 深度约38~52km, 而该区内由人工地震探测剖面(张恩会等, 2013; 王夫运等, 2014; 王帅军等, 2015a)得到的莫霍面深度约33~52km, 二者存在明显差异, 与图3a相比, 采用分区反演方法得到的莫霍面深度(图3b)与人工地震探测结果更加一致, 表明在进行大区域密度界面反演时, 需充分考虑不同构造单元密度界面之间的差异, 采用不同的反演参数。

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	图3 川滇地区莫霍面深度等值线图 a 整体反演结果; b 分区反演结果, 黑色实线是人工地震测深剖面。 AA’ 遂宁-阿坝; BB’ 金川-芦山-乐山; CC’ 丽江-清镇; DD’ 镇康-泸西; EE’ 勐海-耿马-泸水; FF’ 普洱-泸西Fig. 3 The depth of Moho interface in Sichuan-Yunnan region.

图3b是本文根据人工地震探测结果对川滇地区进行重力分区反演得到的莫霍面深度等值线图, 与陈石等(2015)采用重震联合最优化反演得到莫霍面深度具有较好的一致性。从图中可以看出, 整个川滇地区莫霍面深度约34~62km, 位于青藏高原内部的川西北次级块体和松潘-甘孜地块莫霍面深度最大, > 50km, 向周围逐渐变浅; 莫霍面深度变化梯度最大的区域位于松潘-甘孜地块和扬子地块交界部位的龙门山断裂带上; 四川盆地莫霍面深度约38~42km; 滇中次级块体莫霍面深度自西北部的青藏高原向东南部的扬子地块逐渐变浅, 等值线向SE方向呈U型凸起, 变化范围约42~50km; 位于金沙江-红河断裂带以西的滇西地块, 自北向南莫霍面逐渐变浅, 变化范围约33~52km。

莫霍面起伏特征与地壳结构特征和深部动力学过程密切相关。人工地震测深(嘉世旭等, 2014; 王帅军等, 2015b; 徐涛等, 2015)和天然地震层析成像结果(王椿镛等, 2002; 刘启元等, 2009; 黄忠贤等, 2013)均表明: 在青藏高原东南缘的松潘-甘孜地块和川西北次级块体中、下地壳有低速层存在, 地壳较为软弱; 扬子地块的四川盆地在中、下地壳速度较高, 地壳坚硬; 大火成岩省内带攀枝花附近莫霍面局部隆起, 地壳呈现高速异常特征。印度板块向欧亚板块下方俯冲, 造成青藏高原向上隆升、地壳增厚, 受印度板块挤压, 青藏高原东缘松潘-甘孜地块中、下地壳软弱物质E移受到四川盆地强硬地壳的阻挡, 在龙门山断裂带附近形成逆冲推覆构造的同时, 也使得其下方莫霍面厚度发生强烈变化, 形成莫霍面深度变化梯级带; 攀枝花附近的高速异常虽然在一定程度上阻挡了青藏高原东南缘的川西北次级块体地壳物质向S挤出, 但由于其范围较小, 莫霍面变化较为平缓。红河断裂带是滇中次级块体和滇西地块的分界断裂, 它不仅受到青藏高原东南缘川西北次级块体向SE挤出, 还受到滇西地块以西的印缅块体向E挤压和俯冲, 最终导致在其两侧, 莫霍面深度自北向南差异逐渐增加。根据本文结果, 在攀西裂谷带下方莫霍面深度变化平缓, 并未有明显隆升, 与张恩会(2015)和石磊等(2015)采用最新的重力异常反演的结果一致, 石磊通过建立过攀西裂谷的二维密度结果模型认为引起攀西裂谷带高重力异常的原因不是莫霍面隆起, 而是地壳底部壳幔过渡层密度较高引起的, 与超级地幔柱和岩浆的底侵作用有关。

3.2 地壳厚度

由于布格重力异常反演的莫霍面深度是自大地水准面至莫霍面的深度, 当地面高程为0时, 地壳厚度与莫霍面深度相同, 当地面起伏较大时, 地壳厚度等于地面高程加上莫霍面深度。图4是根据川滇地区莫霍面反演结果和高程数据(图1)得到的该区地壳厚度等值线图, 其变化趋势与莫霍面深度(图3b)基本一致。由于川滇地区地形起伏大, 青藏高原海拔> 3i000m, 与四川盆地最大高差达到5i000m, 使得青藏高原与四川盆地之间的地壳厚度差进一步增加, 龙门山地壳厚度变化梯度增大。青藏高原东南缘地壳厚度> 54km, 向高原外围逐渐减小, 川西北次级块体东南侧, 地壳等厚线呈U型向SE向弯曲。滇西地块地壳厚度自北向南逐渐减薄, 变化范围为34~58km。川滇地区的一些深大断裂不仅控制了构造单元边界, 还造成了其下方地壳厚度的剧烈变化, 在龙门山断裂带下方表现为地壳厚度自西向东的快速减薄, 在红河断裂带附近表现为地壳厚度的快速变化。

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	图4 川滇地区地壳厚度分布图Fig. 4 The crustal thickness in Sichuan-Yunnan region.

综上所述, 在青藏高原东南缘, 不同构造单元的地壳结构和深部动力学成因存在差异, 造成青藏高原东缘松潘-甘孜地块与四川盆地之间以挤压环境为主, 在中、上地壳形成龙门山逆冲推覆构造带, 并产生强烈的垂直变形, 青藏高原东缘隆起与外围盆地间形成巨大高差, 地壳厚度变化表现为梯度带特征(嘉世旭等, 2014; 王帅军等, 2015b); 川滇菱形块体自NW向SE地壳厚度逐渐变薄, 虽然其E移物质受到了攀西裂谷带下方高密度体的阻挡, 但其地壳厚度变化不明显, 变化较为平缓; 由于红河断裂带是1条巨型走滑断裂带, 作为滇西地块和滇中次级块体的分界, 该断裂带两侧地壳厚度多为急剧变化(张恩会等, 2013; 王夫运等, 2014), 且自北向南地壳厚度差异不同, 表明该区深部运动过程存在差异。根据川滇地区地壳厚度结果, 青藏高原东南缘地壳增厚是不均匀的, 其物质向周围运移的过程中因受到不同地质构造单元的阻挡及巨型断裂的控制, 造成该区地壳变形复杂, 不能简单套用 “ 大陆逃逸” 模型(Tapponnier et al., 1982)、连续变形模型(England et al., 1986)和下地壳流模式(Royden et al., 1997)。

3.3 对比分析

为进一步分析本文反演的莫霍面深度是否可靠并评价反演结果的精度, 将其与2010年以来最新的人工地震测深结果进行对比, 结果如表2、图5所示, 其中采用的人工地震莫霍面深度均已消除地形起伏的影响, 计算点数指的从地震剖面数字化得到的莫霍面深度数据的个数。从表2中可以看出, 采用分区反演得到的莫霍面深度与人工地震结果具有较好的一致性, 其均方差< 1.7km。

表2 密度界面分区反演和人工地震探测莫霍面深度结果对比分析 Table2 Comparison and analysis on results of Moho interface depth between divisional density interface inversion and artificial seismic exploration

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	图5 莫霍面结果对比 a AA’剖面; b BB’剖面; c CC’剖面; d DD’剖面; e EE’剖面; f FF’剖面Fig. 5 Comparison of Moho interface results.

AA'和BB' 2条剖面(图5a, b)位于研究区北部, 自西向东经过川西北高原、松潘-甘孜地壳转换带和四川盆地, 莫霍面深度逐渐变浅, 在川西北地区, 莫霍面深度约50~57km, 重力反演结果和人工地震探测成果基本一致(嘉世旭等, 2014; 王帅军等, 2015b); 在松潘-甘孜地壳转换带, 莫霍面深度在AA'剖面由高原盆地东南边缘龙日坝断裂的54km逐渐抬升至四川盆地西缘山前断裂的42km, BB'剖面莫霍面深度自西向东由50km逐渐抬升至41km, 重力和人工地震的莫霍面结果在转换带附近存在3~5km的差异, 分析可能是由于地震剖面莫霍面附近速度呈强梯度变化带特征, 而重力反演的是密度差在0.4g/cm³附近变化的密度界面; 在四川盆地, AA'剖面的人工地震探测结果显示莫霍面深度约41~43km, 重力反演的结果约36~40km, 二者存在一定差异, 结合该剖面速度结构, 在四川盆地下地壳和莫霍面之间存在多个速度突跳界面, 重力反演结果得到的莫霍面深度更加接近6.65~6.9km/s的速度突跳界面深度, BB'剖面在四川盆地内通过人工地震和重力得到莫霍面深度结果基本一致, 约40~42km。

CC'剖面位于研究区中部(图5c), 与徐涛等(2015)布设的丽江-清镇人工地震剖面位置相同, 重力反演得到的莫霍面深度自西向东逐渐变浅, 从川滇菱形块体内的50km逐渐抬升至华南地块的39km, 整体变化平缓, 局部起伏不大; 人工地震反演的莫霍面在丽江-小金断裂和小江断裂下方明显下坳, 在攀枝花下方明显隆起, 深度在47~53km之间变化, 与重力结果存在明显差异, 结合速度结构进行分析, 可能与2条断裂带之间下地壳和莫霍面之间速度强梯度带变化有关; 在小江断裂带以东, 地壳速度突跳界面清晰, 人工地震和重力反演结果基本一致。

DD'和FF'剖面(图5d, e)均位于研究区南部, 跨越了红河断裂带。根据人工地震探测结果(张恩会等, 2013; 王夫运等, 2014), 在红河断裂带以西, 地壳速度偏低, 莫霍面较浅, 约33~35km。在红河断裂带附近, 莫霍面深度快速增加至40km左右, 而红河断裂带东侧的扬子块体, 莫霍面深度变化稳定, 约40~42km。在红河断裂带两侧重力反演结果与人工地震探测结果基本一致, 在红河断裂带附近变化特征虽有一定差异, 但莫霍面深度在该处快速增加的趋势一致。

EE'剖面(图5f)位于红河断裂带西侧, 人工地震探测(王帅军等, 2015a)和重力反演结果基本一致, 自南向北, 莫霍面深度逐渐增加, 变化范围约32~38km。

从图5d-f可以看出, 在红河断裂带以西重力整体反演结果与人工地震得到的莫霍面深度整体相差4km左右, 采用不同参数进行分区反演后, 这种区域性差异消失, 表明重力界面反演对初始反演模型依赖性强, 在进行大区域重力反演时, 需根据人工地震探测结果, 充分考虑不同构造单元间反演界面的密度差异, 采用不同的参数进行分区反演。

图5a-c结果表明, 在深大断裂下方地壳速度呈强梯度变化和下地壳速度变化存在多个突跳界面时, 重力反演结果与人工地震存在较大差异, 原因在于重力界面反演时要求界面上下物质层分布比较均匀、稳定且密度差已知, 本文采用的变密度反演模型虽然考虑了密度随深度变化的影响, 但由于川滇地区构造变形复杂, 深大断裂发育, 低速层广泛分布, 使得不同构造单元莫霍面上下物质密度差的分布在反演区域内存在较大差异, 从而导致重力反演结果和人工地震结果在局部存在一定差异。

综上所述, 采用分区反演仅能消除某个构造单元内区域性莫霍面差异, 而无法解决由于地壳局部速度结构突变引起的重力莫霍面反演和人工地震测深结果之间的差异问题。

4 讨论与结论

本文利用滑动平均法从川滇地区布格重力异常场分离出主要反映莫霍面起伏的低频布格重力异常场, 将由地震模型转换并经过高程改正的密度模型作为初始模型, 根据不同构造单元之间莫霍面上、下密度差不同, 采用Parker法对低频布格重力异常场进行分区反演, 得到了该区莫霍面深度和地壳厚度分布特征。同时, 充分考虑布格重力异常和人工地震探测模型的差异, 在进行反演和结果对比时扣除大地水准面以上部分地震结果的影响, 并得到以下认识:

(1)位于研究区西北部的松潘-甘孜地块和川西北次级块体地处青藏高原东南缘, 其莫霍面深度和地壳厚度表现为从高原边缘向内部加深和增厚, 分别为52~62km和54~66km; 研究区东北部主要为四川盆地(扬子地块), 由于其高程变化较小, 其莫霍面深度和地壳厚度基本一致, 约38~42km; 研究区北部自西向东, 莫霍面深度和地壳厚度在松潘-甘孜地壳转换带下方变化梯度最大; 研究区西南部的川滇菱形块体内莫霍面深度和地壳厚度自NW向SE逐渐减小, 分别为42~62km和44~66km; 研究区西南部位于金沙江-红河断裂带以西的滇西地块, 自北向南莫霍面深度和地壳厚度逐渐变小, 分别为33~52km和34~54km。

(2)青藏高原E移物质受坚硬的四川盆地阻挡, 在龙门山断裂带下方形成莫霍面深度和地壳厚度变化梯度带; 红河断裂带两侧莫霍面深度和地壳厚度自北向南差异逐渐增加, 推测可能是由于红河断裂带受到青藏高原东南缘川西北次级块体SE向挤出和滇西地块以西的印缅块体向E挤压、俯冲作用的共同影响。

(3)根据密度界面分区反演结果, 在攀西裂谷带下方莫霍面深度和地壳厚度变化平缓, 并未有明显隆升, 与石磊(2015)和张恩会等(2015)采用的最新重力异常反演所得的结果一致, 石磊通过建立过攀西裂谷的二维密度结果模型认为引起攀西裂谷带高重力异常的原因不是莫霍面隆起, 而是地壳底部壳幔过渡层密度较高, 与超级地幔柱和岩浆的底侵作用有关。

(4)重力反演结果进一步映证了地震剖面的成果(表2, 图5), 并在横向上扩展了对研究区莫霍面起伏变化的认识。重力和人工地震结果差异较大的地区多位于莫霍面深度和地壳厚度急剧变化的地区, 如松潘-甘孜地壳转换带、红河断裂带及一些深大断裂带附近, 一方面体现出不同方法的应用差异, 同时也体现出在构造转换带壳幔边界可能为一复杂过渡带而不是间断界面。

(5)将重力反演得到的莫霍面深度模型和已有人工地震探测结果进行比对, 发现采用密度界面分区反演方法得到的莫霍面深度在红河断裂带以西的滇西块体与人工地震探测结果更加一致, 计算二者均方差变化范围为0.72~1.67km。该对比结果表明在不同构造单元地壳速度、密度结构存在明显差异区域, 以高分辨地震探测结果为约束, 开展分区密度界面反演工作, 可有效提高反演结果的可靠性。

(6)川滇地区莫霍面深度分布明显受印度板块与欧亚板块碰撞及其向中南半岛侧向俯冲的制约。

致谢田晓峰研究员、邓晓果工程师提供了相关基础资料, 审稿专家对本文提出了建设性修改意见, 在此表示衷心感谢。

The authors have declared that no competing interests exist.

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17	王帅军, 刘保金, 张建狮, 等. 2015a. 南北地震带滇西南地区地壳速度结构与构造研究: 勐海-耿马-泸水深地震探测剖面成果[J]. 中国科学(D辑), 45(12): 1853-1865. WANG Shuai-jun, LIU Bao-jin, ZHANG Jian-shi, et al. 2015a. Study on the velocity structure of the crust in Southwest Yunnan of the North-South Seismic Belt: Results from the Menghai-Gengma-Lushui deep seismic sounding profile[J]. Science in China(Ser D), 45(12): 1853-1865(in Chinese). [本文引用:1]
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2004

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白志明, 王椿镛. 2004. 云南遮放-宾川和孟连-马龙宽角地震剖面的层析成像研究[J]. 地球物理学报, 47(2): 257-267.

BAI

Zhi-ming

, WANG

Chun-yong

. 2004. Tomography research of the Zhefang-Binchuan and Menglian-Malong wide-angle seismic profiles in Yunnan Province[J]. Chinese Journal of Geophysics, 47(2): 257-267(in Chinese).

Based on the finite difference inversion and ray inversion method, the crust and upper mantle's structure on the Zhefang—Binchuan and Menglian—Malong wideangle seismic profiles, both of which are located in Yunnan province,are tomographyed using the geophysical data of traveltime, amplitude ratio and Bouger anomaly. Thus some new recognitions about the geodynamics and the seismotectonic environment are derived. The crustal thickness of the Zhefang—Binchuan profile is 35～46km，and that of the Menglian—Malong profile is 33～44.5km. The geometry of the Moho interface is like that given by Hu Hongxiang. The P wave velocity on the top of the mantle of some places is relatively low and the fluctuating range of the velocity is very large, which may indicates that the Yunnan region is a typical tectonic active area. Moreover, there exits a prominent consistency between the shallow and deep structures, which implys that the activity of shallow material always has a deep background. The velocity structure of the Zhefang—Binchuan profile indicates that there exists a large low velocity anomaly across the crust to the east of the Nujiang fault exposed on the ground，and this maybe related with the deep material upwelling. The characteristic of the large faults which are the borders between some first order tectonic units can also be derived by both of the velocity structure profiles: the Honghe fault is a superfault that cut the lithosphere，the Nujiang fault cuts deeply in the crust and even stretches downward into the top of the upper mantle, yet the Changning—Shuangjiang fault has a listric shape with a small dip angle, which may suggest that its incision depth is not very deep. The large earthquakes in Yunnan province always have a relationship with the large and deep faults that stretch into the upper mantle. Some earthquakes with shallow focal depths are generally located at converge positions of faults within the upper and middle crust or the positions where the velocity contours on the belt between the high and low velocity anomaly blocks are crooked. It is inferred estimated that these locations are prone to the accumulation of the energy and the regional stress.

1 Institute of Geology and Geophysics， Chinese Academy of Sciences， Beijing 100029， China 2 Institute of Geophysics， China Seismology Bureau， Beijing 100081， China

依据有限差分反演和射线反演的方法，利用走时、振幅比和重力布格异常数据对云南地区遮放—宾川和孟连—马龙宽角地震剖面的地壳上地幔结构进行层析成像研究. 遮放—宾川测线地壳厚度为35～46km，孟连—马龙测线地壳厚度33～44.5km. 局部位置上地幔顶部P波速度值偏低，速度值变化范围大，反映出云南地区是典型的构造活动区的特点. 地壳上地幔结构存在一定程度的深浅构造一致性，意味着浅部物质活动存在深部背景. 遮放—宾川剖面速度结构显示地表怒江断裂东侧存在贯穿地壳的大规模低速异常，可能与深部物质上涌活动有关. 遮放—宾川线和孟连—马龙线速度结构显示作为一级构造单元分界线的红河断裂是超壳断裂，怒江断裂深及上地幔. 而昌宁—双江断裂显示为低角度铲式断层，意味着该断裂切割并不深. 云南地区强震的发生往往与延伸到上地幔的深大断裂有关，且一些浅源地震经常位于中上地壳深大断裂与其他断裂的交汇部位、高速块体与低速块体接触带上速度等值线弯曲的位置. 推测这样的位置有利于能量和区域应力的积累.

... 白志明等, 2004 ...

2015

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1987

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崔作舟, 卢德源, 陈纪平, 等. 1987. 攀西地区的深部地壳结构与构造[J]. 地球物理学报, 30(6): 566-580.

CUI

Zuo-zhou

, LU

De-yuan

, CHEN

Ji-ping

, et al. 1987. The deep structural and tectonic features of the crust in Panxi area[J]. Chinese Journal of Geophysics, 30(6): 566-580(in Chinese).

This paper discusses the deep geological features in Panxi region obtained by deep seismic sounding from 1984 to 1985. This region has a thick crust of 50-60 km, and possesses multi-layed structure with lower velocity layers alternating with the higher velocity ones and fault-block tectonices. Of the five main velocity interfaces, R4 is steady and clear and may be regarded as the interface between the upper and lower crust; Re is steady and shows stronger reflection. It is the MOHO. The MOHO is deeper in the north and shallower in the south （56 -50 km） along the tectonic zone. It is deeper in the west and shallower in the east （60-48 km） across the zone. The upper-crustal thickness is thinner and the velocity is non-homogeneous. The lower-crustal is thicker and the yelocity is steady within the tectonic zone. The lower-velocity layers at the bottom of the upper-crust is thinner and shallower inside than outside of the zone. The P, velocity is lower, 7.54-7.80 km/s, and belongs to the crust-mantle transition zone. Its thickness is 13-22 km. Xiaojiang fault, Sikai fault, Anninghe fault and Jinhe fault etc. are crustal and ultracrust faults and they are mostly thrusts faults. Most of these structural and tectonic features show that this tectonic zone is a young erogenic zone of the continental plateau.

The 562 Comprehensive Geological Brigade of the Chinese Academy of Geological Sciences, Hebei Sanhe

根据1984—1985年地震测深资料,论述了攀西地区的深部地质特征。该区地壳厚50—60km;具高、低速相间的多层结构及断块构造;五个主要速度界面中,界面R 4 稳定且清晰,为上、下地壳的分界面,R 6 稳定并有较强的能量反射,为壳、幔之间的界面（莫霍面）,莫霍面沿构造带北深南浅（56—50km）,横穿构造带西深东浅（60—48km）。构造带内的上地壳较薄,纵横速度变化均较大,而下地壳较厚,速度较均匀,上地壳底部的低速层,在构造带内较带外薄而浅,P n 速度较低,为7.54—7.80km/s,属壳-幔过渡带,厚13—22km。小江、四开、安宁河及金河等断裂为超壳型或壳内断裂,多为逆冲断层。该构造带的各种深部特征表明它为大陆高原型年轻构造带。

... 2)攀西裂谷带下方莫霍面是否隆升?隆升规模有多大?不同地球物理结果存在差异(崔作舟等, 1987 ...

... 崔作舟等, 1987 ...

1985

0.0

... 王帅军等, 2015a), 而重力反演结果多为40~45km(冯锐, 1985 ...

... 此外, 为获得川滇地区莫霍面深度的区域变化特征, 一些学者还利用重力资料来反演莫霍面深度(冯锐, 1985 ...

... 1 莫霍面深度图3a是川滇地区莫霍面整体反演结果, 该结果与前人采用重力反演得到的莫霍面深度具有较好的一致性(冯锐, 1985 ...

2013

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黄忠贤, 李红谊, 胥颐. 2013. 南北地震带岩石圈S波速度结构面波层析成像[J]. 地球物理学报, 56(4): 1121-1131.

HUANG

Zhong-xian

, LI

Hong-yi

, XU

. 2013. Lithospheric S-wave velocity structure of the North-South Seismic Belt of China from surface wave tomography[J]. Chinese Journal of Geophysics, 56(4): 1121-1131(in Chinese).

This paper uses surface wave data from natural earthquakes and a tomographic method to study the S-wave velocity structure and anisotropy of the lithosphere of North-South Seismic Belt and adjacent regions. The result indicates that the east margin of the seismic belt is not only a zone of rapid change of crustal thickness, but also a remarkable boundary between different crustal velocities. To its west the S-wave velocity of the middle and lower crust is obviously lower than that on the east side, and strong earthquakes generally occur within or at the border of the low velocity regions. The S-wave velocity of middle-lower crust in the east margin of Tibetan Plateau is obviously lower than that of normal continental crust; low velocity zones (LVZ) exist at depths about 25 similar to 45 km in the crust of Songpan-Garze block and the western part of Chuan-Dian block. These low velocity features are connected with the low velocities of the plateau proper, which facilitates the lateral flow of lower crustal material. The anisotropy patterns of the crust is consistent with the lower crust flow model, that is, the lower crust material moves around the eastern Himalayan syntaxis and the eastward movement is diverted to south and northeast when blocked by the rigid Yangtze crust. The result of our surface wave tomography supports the lower crust flow model for crustal movement of Tibetan Plateau. The lithosphere of the North-South Seismic Belt has similar thickness with that of Erdos and Yangtze on its east, but with relatively lower velocity. At the top of upper mantle in the west Chuan-Dian block (from Moho to about 88 km) the shear velocity is abnormally low; in the upper mantle lid of Songpan-Garze block there is a low velocity layer between about 90 and 130 km depth. The velocity pattern of the upper mantle is remarkably different from that of the crust; there is an NNE-trending high velocity zone between the plateau proper and western Sichuan-Yunnan region, which may hamper the eastward movement of mantle material. The anisotropy of upper mantle is weaker and exhibits an obviously different pattern from the crustal anisotropy. Therefore, it is considered that the modes of tectonic movement of crust and upper mantle of Tibetan Plateau are different, and the weak lower crust provides the condition for decoupling of crust and mantle movement.

Huang Zhong-Xian 1 ;Li Hong-Yi 2 ;Xu Yi 3 ;

本文利用天然地震面波记录和层析成像方法,研究了南北地震带及邻近区域的岩石圈S波速度结构和各向异性特征.结果表明南北地震带的东边界不但是地壳厚度剧变带,也是地壳速度的显著分界.其西侧中下地壳的S波速度显著低于东侧,强震大多发生在低速区内部和边界.青藏高原东缘中下地壳速度显著低于正常大陆地壳,在松潘甘孜地块和川滇地块西部大约25～45 km深度存在壳内低速层;这些低速特征与高原主体的低速区相连,有利于下地壳物质的侧向流动.地壳的各向异性图像与下地壳流动模式相符,即下地壳物质绕喜马拉雅东构造结运动,东向的运动遇到扬子坚硬地壳阻挡而变为向南和向北东的运动.面波层析成像结果支持青藏高原地壳运动的下地壳流动模型.南北地震带的岩石圈厚度与其东侧的扬子和鄂尔多斯地块相似但速度较低.川滇西部地块上地幔顶部(莫霍面至88 km左右)异常低速;松潘甘孜地块上地幔盖层中有低速夹层(约90～130 km深度).岩石圈上地幔的速度分布图像与地壳显著不同,在高原主体与川滇之间存在北北东向高速带,可能会阻挡地幔物质的东向运动.上地幔各向异性较弱且与地壳的分布图像显然不同.因此青藏高原岩石圈地幔的构造运动具有与地壳不同的模式,软弱的下地壳提供了壳幔运动解耦的条件.

... 黄忠贤等, 2013)均表明: 在青藏高原东南缘的松潘-甘孜地块和川西北次级块体中、下地壳有低速层存在, 地壳较为软弱 ...

2014

0.0

... 嘉世旭等, 2014 ...

... 在青藏高原东北缘的松潘-甘孜地块莫霍面深度约50~60km, 四川盆地地壳厚度约40~45km(嘉世旭等, 2014 ...

... 人工地震测深(嘉世旭等, 2014 ...

... 综上所述, 在青藏高原东南缘, 不同构造单元的地壳结构和深部动力学成因存在差异, 造成青藏高原东缘松潘-甘孜地块与四川盆地之间以挤压环境为主, 在中、上地壳形成龙门山逆冲推覆构造带, 并产生强烈的垂直变形, 青藏高原东缘隆起与外围盆地间形成巨大高差, 地壳厚度变化表现为梯度带特征(嘉世旭等, 2014 ...

... AA'和BB' 2条剖面(图5a, b)位于研究区北部, 自西向东经过川西北高原、松潘-甘孜地壳转换带和四川盆地, 莫霍面深度逐渐变浅, 在川西北地区, 莫霍面深度约50~57km, 重力反演结果和人工地震探测成果基本一致(嘉世旭等, 2014 ...

2015

0.0

... 姜永涛等, 2015 ...

2009

0.0

刘启元, 李翌, 陈九辉, 等. 2009. 汶川 M_S8. 0地震: 地壳上地慢S波速度结构的初步研究[J]. 地球物理学报, 52(2): 309-319.

LIU

Qi-yuan

, LI

, CHEN

Jiu-hui

, et al. 2009. Wenchuan M_S8. 0 earthquake: Preliminary study of the S-wave velocity structure of the crust and upper mantle[J]. Chinese Journal of Geophysics, 52(2): 309-319(in Chinese).

On 12th of May, 2008, a devastating M S 8.0 event shocking the global world occurred in the Wenchuan region of Sichuan province. Historically, the same kind of earthquakes is very rare inside of the continent. The study on the tectonic environment of this event is crucial for understanding its genesis. From the teleseismic waveform data recorded by the dense large-scale movable seismic array in the western Sichuan by the State Key Laboratory of Earthquake Dynamics, Institute of Geology, China Earthquake Administration (CEA), we investigate the S-wave velocity structure of the crust and upper mantle within the depth range of 120 km and averaged Poisson′s ratio over the crust beneath 19 stations distributed along the profile of 31°N by using the non-linear receiver function inversion technique. This profile is about 420 km long and crosses the main shock area. Our results show the differences of the crustal structure among the blocks of Chuandian, Songpan-Garze and Sichuan basin. Their main features can be summarized as follows: (1)the crust-mantle boundary in the foreland of the Sichuan basin declines westward and has been deformed obviously; The crustal thickness has lateral variations of 46～52 km; the velocity of middle and lower crust has lateral variations; the Poisson′s ratio averaged over the crust reaches up to 0.28～0.31; however, the crust is hard nearby the Longmen Shan faults, where the Poisson′s ratio averaged over the crust is only 0.2; (2)in the Songpan-Garze block, from the west to the east, the crustal thickness becomes thinner from 60 km to 52 km; in the depth range of 14～50 km exists a wedged low-velocity zone with the S-wave velocity of 2.75～3.15 km/s, whose thickness decreases from ～30 km in the western side to ～15 km in the eastern side; the Poisson′s ratio averaged over the crust containing the low-velocity zone reaches up to 0.29～0.31; (3)the crustal structure of the Chuandian block looks simple to the west of the Xianshuihe faults and the crustal thickness reaches to 58 km; but a high-velocity layer with thickness of ～10 km exists in the depth of 26 km; the Poisson′s ratio averaged over the crust is ～0.25; (4)within the crust beneath the Wenchuan earthquake region exists a high-velocity structure of ～4.0 km/s at the depth of 12～23 km, and below it exists a low-velocity structure, where the Poisson′s ratio averaged over the crust is 0.31～0.32; the aftershocks of the Wenchuan earthquake are mainly distributed in the region of the upper crust with high-velocity structure. Our results manifest that the Songpan-Garze block has a soft and weakened crust, and the westward subduction of the Sichuan basin does not exist. It could be inferred that under the long-term pressure eastward from the Tibetan plateau, the Songpan-Garze block obstructed by the Sichuan basin has been deformed greatly and a large energy of deformation has been accumulated inside before the Wenchuan earthquake and that the upper crust decoupled with the lower crust at the top boundary of the low-velocity zone leads to the listric thrust of the upper crust. The rigid upper crust with high-velocity underneath the Wenchuan earthquake and its adjacent region as well as the obstruction of the Sichuan basin make it possible to accumulate high stress with low strain rate. The vast strain energy accumulated in the long-term deformation within the Songpan-Garze block should be the dynamic source of the Wenchuan great earthquake.

1 State Key Laboratory of Earthquake Dynamics, Institute of Geology, China Earthquake Administration, Beijing 100029, China 2 Kangding Central Seismic Station, Sichuan Earthquake Administration, Kangding 626001,China

2008年5月12日我国四川省汶川地区发生了震惊世界的 M S 8.0地震.历史上，同类地震在大陆内部极为罕见.该地震深部构造背景的研究对理解其成因极为重要.本文利用中国地震局地质研究所地震动力学国家重点实验室在川西地区布设的大规模密集流动宽频带地震台阵记录的远震P波波形数据和接收函数非线性反演方法，得到了沿北纬31°线的19个台站下方120 km深度范围内的S波速度结构及台站下方地壳的平均泊松比.该观测剖面穿越了主震区，总长度约为420 km. 我们的结果揭示了川滇地块、松潘—甘孜地块和四川盆地三个不同地块构造差异.上述三个地块的地壳结构特征可以概括为：（1）四川盆地前陆壳幔界面向西侧倾斜并有较为明显的横向变形，地壳厚度存在46～52 km的横向变化，中下地壳S波速度存在横向变化，地壳平均泊松比值较高（0.28～0.31），但在龙门山断裂带附近，显示了坚硬地壳的特征,地壳平均泊松比仅为0.2；（2）松潘—甘孜地块地壳厚度由西侧靠近鲜水河断裂的60 km，向东减薄为52 km，在14～50 km深度范围内存在S波速度2.75～3.15 km/s的楔状低速区，其厚度由西侧的～30 km向东逐渐减薄为～15 km，相应区域的地壳平均泊松比高达0.29～0.31；（3）鲜水河断裂西侧,川滇地块地壳结构相对简单，地壳厚度为58 km，并在26 km深度存在约10 km厚度的高速层，地壳内平均泊松比约为0.25；（4）汶川大震区在12～23 km深度上具有近乎4.0 km/s的S波高速结构，而其下方的地壳为低速结构，地壳平均泊松比0.31～0.32，汶川大震的余震序列主要分布在高速介质区域内. 本文的结果表明松潘—甘孜地块的地壳相对软弱；而且并不存在四川盆地向西侧的俯冲.我们认为在青藏高原东向挤压的长期作用下，四川盆地强硬地壳的阻挡作用可导致松潘—甘孜地块内部蓄积很大的应变能量以及上、下地壳在壳内低速层顶部边界的解耦，在龙门山断裂带附近形成上地壳的铲形逆冲推覆.汶川大地震及其邻近区域所具有的坚硬上地壳和四川盆地的阻挡作用为低应变率下的高强度应力积累创造了必要条件，而松潘—甘孜地块长期变形积累的高应变能构成了孕育汶川大地震的动力来源.

... 刘启元等, 2009 ...

2005

0.0

2008

0.0

... 路晓翠, 2008 ...

2012

0.0

... 施发奇等, 2012) ...

2015

0.0

... 石磊等, 2015 ...

2003

0.0

2002

0.0

... 王帅军等, 2015a), 该断裂带以西, 莫霍面深度和密度差均小于断裂带以东, 且该断裂可能深切至莫霍面(王椿镛等, 2002 ...

... 徐涛等, 2015)和天然地震层析成像结果(王椿镛等, 2002 ...

2003

0.0

2014

0.0

王夫运, 潘素珍, 刘兰, 等. 2014. 玉溪-临沧剖面宽角地震探测: 红河断裂带及滇南地壳结构研究[J]. 地球物理学报, 57(10): 3247-3258.

WANG

Fu-yun

, PAN

Su-zhen

, LIU

Lan

, et al. 2014. Wide angle seismic exploration of Yuxi-Lincang profile: The research of crustal structure of the Red River fault zone and southern Yunnan[J]. Chinese Journal of Geophysics, 57(10): 3247-3258(in Chinese).

Yunnan province is located in the southern section of North South seismic belt, the seismicity of this area has the features of high frequency, high strength, and small earthquakes are almost everywhere; it is one of the strongest earthquake regions in the China continental interior. Southern Yunnan crosses a number of important geological tectonic units and series of seismic belts. Among them, the red river fault zone is a large strike slip fault zone crossing Yunnan province, and as the boundary fault between Indochina block and South China block, it has important significance for understanding the interaction of plates and geodynamic background. In 2010, China Earthquake Administration launched the China seismological array exploration project-southern section of North South seismic belt. According to the research purpose and requirements of this project, a nearly EW-trending deep seismic wide-angle reflection/refraction profile was laid out across the Red River fault zone in central and western Yunnan. In this paper, the crustal structure and seismogenic background of the Red River fault zone and the southern Yunnan area is studied by using this sounding profile. The results show that: the crust along this profile thickens from west to east, which is probably bounded by red river fault zone, the west part is thinner, about 34 km, the east part is thicker, about 44 km. There is obvious difference in the velocity structure on the two sides of the red river fault zone, and the velocity is lower in west and significantly higher in east. From the seismic phase and the crustal structure we obtained, the two sides of the red river fault zone are characterized of different crustal structure from shallow to deep, which demonstrates great difference of lithology on the two sides of this paleo suture.

[Wang Fu-Yun; Pan Su-Zhen; Liu Lan; Liu Bao-Feng; Zhang Jian-Shi; Deng Xiao-Guo; Ma Ce-Jun; Zhang Cai-Jun] China Earthquake Adm, Geophys Explorat Ctr, Zhengxhou 450002, Peoples R China.

云南位于南北地震带南段,地震活动具有频度高、强度大的特点,中小地震几乎遍及云南南部,是中国大陆内部地震活动最强的地区之一.滇南地区跨越多个重要的地质构造单元和多条地震带,其中红河断裂带是跨越该地区的一条大型的走滑断裂带,作为印支地块和华南地块两大地块的分界断裂,对人们认识板块相互运动及其深部动力学背景具有重要意义.中国地震局于2010年启动了"中国地震科学台阵探测——南北地震带南段"项目,在云南省中西部跨越红河断裂带布设一条近东西向的深地震宽角反射/折射探测剖面,本文利用该东西向深地震宽角反射/折射剖面来研究红河断裂带及滇南地区详细的地壳结构及其孕震背景.研究结果表明:沿测线地壳结构呈西薄东厚的特征,以红河断裂带为界,断裂带以西地壳较薄,约34 km,以东地壳加厚至44 km左右;红河断裂带两侧速度结构具有明显的差异,断裂带西侧速度较低,东侧速度明显偏高.由震相特征及获取的地壳结构可以看出,红河断裂带两侧由浅至深速度结构的异常特征说明该古缝合带两侧块体地壳结构岩性的巨大差异性.

... 王夫运等, 2014 ...

... 王夫运等, 2014), 且自北向南地壳厚度差异不同, 表明该区深部运动过程存在差异 ...

... 王夫运等, 2014), 在红河断裂带以西, 地壳速度偏低, 莫霍面较浅, 约33~35km ...

2015

0.0

2015

0.0

1986

0.0

熊绍柏, 滕吉文, 尹周勋, 等. 1986. 攀西构造带南部地壳与上地幔结构的爆炸地震研究[J]. 地球物理学报, 29(3): 235-244.

XIONG

Shao-bai

, TENG

Ji-wen

, YIN

Zhou-xun

, et al. 1986. Explosion seismological study of the structure of the crust and upper mantle at southern part of the Panxi tectonic belt[J]. Chinese Journal of Geophysics, 29(3): 235-244(in Chinese).

The Institute of Geophysics, Academia Sinica conducted some experiments of seismic refraction profiling crossing the Panzhihua region in 1984. The Panzhihua region is located at the southern part of the Panxi tectonic belt. We have analyzed six record sections for the W-E profile which extends 350 km. The results are as follows: （1） The crust of the Panxi region can be divided into three main layers Avith thicknesses of about 20, 20, and 15km respectively. （2） The thickness and the average velocity of the whole crust is 55km and 6.22 km/s respectively. （3） There is a high-velocity rock body near the surface of the axial area of the tectonic belt, and it is probably related to the enrichment of the Panzhihua type sefstr（?）mite in this district. （4） There is a low-velocity zone with a thickness of about 9-14 km a,t the lower part of the midcrust. The top of this low-velocity zone is located at about 23-27 km deep from the surface. The consistence of this result with the distribution of earthquake foci and the depth of Curie isotherm indicates that the existence of the low-velocity zone maybe related to the thermal state of the crust medium. （5） There are several faults which reach into the upper mantle and a high-velocity interlayer at the top of the lower crust. These may signify intrusion of the mantle substance into the crust. （6） A velocity VPn of 7.62-7.90 km/s at the uppermost mantle is consistent with that of recent continental rifting zone. After comparison with other regions in the world, we infer that the Panxi region is perhaps a paleorift zone, but it was strongly transformed by later period's tec-togenesis.

Institute of Geophysics, Academia Sinica

根据1984年攀西地区南部爆炸地震折射剖面资料的研究结果表明,本区的地壳厚度约为55km,且可分为20km、20km和15km厚的三个主要构造层。地壳的平均P波速度为6.22km/s。在深度23—27km之下的中地壳下部有一个厚9—14km的P波低速区,这一结果与其它地球物理观测资料相当吻合。上地幔顶部的P波速度为7.62—7.90km/s,与现代大陆裂谷区或构造活动地区的P_n波速度一致。另外,位于构造带轴部地区的渡口市一带,上地壳中有一高速岩体,下地壳中有高速夹层以及有些断裂带可能延伸到上地幔顶部,均表明地壳中曾经有地幔物质侵入。通过研究,我们推断这个地区有可能是一个被后期构造运动强烈改造过的、至今仍保留有一些裂谷构造残迹的古裂谷带。

... 自20世纪80年代以来, 众学者在川滇地区布设了多条人工深地震探测剖面(熊绍柏等, 1986 ...

2015

0.0

徐涛, 张忠杰, 刘宝峰, 等. 2015. 峨眉山大火成岩省地壳速度结构与古地幔柱活动遗迹: 来自丽江-清镇宽角地震资料的约束[J]. 中国科学(D辑), 45(5): 561-576.

Tao

, ZHANG

Zhong-jie

, LIU

Bao-feng

, et al. 2015. Crustal velocity structure in the Emeishan large igneous province and evidence of the Permian mantle plume activity[J]. Science in China(Ser D), 45(5): 561-576(in Chinese).

峨眉山大火成岩省是中国境内唯一被国际学术界认可的大火成岩省, 普遍认为其形成与古地幔柱有关. 以往对峨眉山古老地幔柱事件的识别, 主要依靠地质地球化学等资料, 缺少深部地球物理探测结果的约束和支持. 为此, 我们利用“丽江-攀枝花-清镇”剖面的人工源宽角地震数据重建该地区地壳速度结构, 以便更好地理解峨眉山大火成岩省的深部结构与属性特征. 前人根据茅口灰岩的剥蚀程度, 将峨眉山大火成岩省从分布空间上划分为内、中、外三个带. 跨越内、中、外带剖面地震探测结果显示: (1) 沿剖面结晶基底的平均深度在2 km左右. (2) 中地壳平均速度结构为6.2~6.6 km/s; 内带局部呈现大约幅值为0.1~0.2 km/s的高速异常; 下地壳速度结构, 在内带为6.9~7.2 km/s; 中带和外带偏低, 为6.7~7.0 km/s; 在内带和中带交界附近, 受小江断裂带的影响, 上、中、下地壳均呈现相对低速异常特征. (3) 小江断裂两侧, 尤其东侧地壳平均速度较低, 且固结地壳的平均速度也较低, 初步认为小江断裂至少向地下延伸至40 km以深, 可能切穿整个地壳. (4) 沿剖面Moho面深度, 内带范围内深约47~53 km, 中间呈上隆的特征; 中带深约42~50 km, 外带深约38~42 km, 中带至外带, Moho面逐渐变浅. 内带Moho面局部隆起、(固结)地壳呈现高速异常特征, 可能是二叠纪地幔柱活动引起的底侵作用及岩浆上侵的结果, 为古地幔柱的活动遗迹.

... 徐涛等, 2015), 获得了剖面下精细的地壳上地幔二维速度结构、莫霍面深度及地壳厚度 ...

... 徐涛等, 2015)和天然地震层析成像结果(王椿镛等, 2002 ...

2005

0.0

... 张忠杰等, 2005 ...

2013

0.0

张恩会, 楼海, 嘉世旭, 等. 2013. 云南西部地壳深部结构特征[J]. 地球物理学报, 56(6): 1915-1927.

ZHANG

En-hui

, LOU

Hai

, JIA

Shi-xu

, et al. 2013. The deep structure characteristics beneath western Yunnan[J]. Chinese Journal of Geophysics, 56(6): 1915-1927(in Chinese).

One two-dimensional P wave velocity model of the crust and uppermost mantle was obtained based on the integrative interpretation of travel-time data and amplitude information from the deep seismic sounding experiment on the Puer-Luxi profile, western Yunnan. Our results show strong lateral variations in crustal thickness along the profile, which varies from about 35 km in the southwest to 43 km in the northeast Yunnan. Average crustal P velocities are low with respect to the global average, varying from 5. 9 to 6. 13 km/s. Combined with previous joint inversion results of receiver function and surface wave, average crustal Poisson's ratio (sigma) is calculated and our results show that sigma varies from 0. 23 in the southwest part of the profile to 0. 25 towards the northeast part of the profile beneath the western Yunnan. The low P wave velocity and sigma for the upper crust layer beneath the southwest part of the profile is indicative of felsic rocks rich in quartz in the alpha state, while the relative high P wave velocity and sigma for the upper crust layer under the northeast part of the profile is indicative of rocks of granitic and granodioritic composition. The P wave velocity and sigma for the lower crust layer is 6. 25 similar to 6. 75 km/s and 0. 24 similar to 0. 26 km/s beneath the profile, which can be explained by felsic gneisses in the upper part of the lower crust transitioning to amphibolite in the lower part. Our crustal velocity model shows remarkable contrasts across the Red River fault and the velocity difference becomes gentler with increasing depth. The crustal thickness across the Red River fault is also significantly different. The variation of the velocity and crustal thickness across the Xiaojiang fault is not so remarkable.

Zhang En-Hui 1 ;Lou Hai 1 ;Li Yong-Hua 1 ;Jia Shi-Xu 2 ;

在云南西部,穿过红河、小江断裂带完成了一条长360 km、呈北东向的深地震宽角反射/折射剖面.通过对该测线的观测资料进行一维、二维模拟解释,得到了沿剖面的二维地壳速度模型.研究结果显示,沿测线Moho界面埋深横线变化大,其西南侧Moho埋深约35 km,东北侧Moho最大埋深可达43 km.沿剖面从西南到北东方向,地壳平均P波速度从5.9 km/s逐渐增加到6.13 km/s,但显著低于全球大陆平均值.结合以往的接收函数和面波联合反演结果,我们推算沿测线从西南到东北,其下方地壳泊松比介于0.23~0.25之间.剖面西南侧上地壳具有异常低的P波速度和泊松比,暗示其下方上地壳以 α -相长英质组分为主;而剖面东北上地壳相对较高的P波速度和泊松比则暗示其物质组成以花岗岩-花岗闪长岩为主.研究区下地壳的P波速度和泊松比分别介于6.25~6.75 km/s和0.24~0.26 km/s之间,暗示其上部组成以花岗岩相的片麻岩为主,而下部组成则以角闪石类岩石为主.红河断裂两侧地壳速度显著不同,从浅到深其速度差异逐渐变弱,但红河断裂两侧地壳厚度变化较大.而小江断裂下方两侧地壳速度和地壳厚度变化并没有红河断裂那么明显.

... 3)在云南中南部地区通过地震剖面得到的莫霍面深度约32~40km(张恩会等, 2013 ...

... 王帅军等, 2015b), 云南地区地壳厚度在红河断裂两侧变化较大(张恩会等, 2013 ...

... 张恩会等, 2015), 在滇西地块内莫霍面自北向南逐渐变浅, 深度约38~52km, 而该区内由人工地震探测剖面(张恩会等, 2013 ...

... 由于红河断裂带是1条巨型走滑断裂带, 作为滇西地块和滇中次级块体的分界, 该断裂带两侧地壳厚度多为急剧变化(张恩会等, 2013 ...

... 根据人工地震探测结果(张恩会等, 2013 ...

2015

0.0

张恩会, 石磊, 李永华, 等. 2015. 基于抛物线密度模型的频率域三维界面反演及其在川滇地区的应用[J]. 地球物理学报, 58(2): 556-565.

ZHANG

En-hui

, SHI

Lei

, LI

Yong-hua

, et al. 2015. 3-D interface inversion of gravity data in the frequency domain using a parabolic density-depth function and the application in Sichuan-Yunnan region[J]. Chinese Journal of Geophysics, 58(2): 556-565(in Chinese).

As an important way to reveal the internal structure of the earth, inversion of the density interface is a main subject of gravity research for a long time. Inversion of field data in the frequency domain provides a quick and efficient data analysis method. Combining the advantages of the frequency domain and parabolic density function, this paper presents a processing method for gravity anomaly data of a three-dimensional underground interface using parabolic density-depth function in the frequency domain. The method we used to make forward modeling of the gravity anomaly is based on the algorithm proposed by Parker and Oldenburg which uses constant density contrast. We substituted the constant density function in gravity forward formula for the parabolic density function. Then the Fast Fourier Transform (FFT) was applied to both sides of the equation. We derived the gravity anomaly formula of 3D density interface with parabolic density contrast after calculating the involved integral. To invert the density interface depth, an iterative algorithm was preformed to adjust the interface depth step by step until the difference between the theoretical anomalies and observations reduced to the threshold value. In addition, in order to avoid the divergence of the algorithm which is difficult to avoid for the calculation in the frequency domain, we also added a low-pass filter to the codes. We applied our method to a theoretical model which has 91×71 grid data with 10 km interval in x -axis and y -axis, and a complex 3D interface with parabolic density contrast variation in depth. In the synthetic test, we compared the method proposed in this paper with the constant, exponential and binomial functions. Besides the points with acute topography fluctuation, the results show that the inversion using parabolic function provides good and stable estimates of the interface depth of the theoretical model with RMS 0.02 km, and that the constant density function inversion gives the worst estimate of the theoretical model. According to the comparison, the choice of density parameters is a key factor in interface inversion. For the density of real situation, which varies more rapidly at smaller depth and less rapidly at larger depth, the method provides better approximations to density interface depth. In addition, we applied our method to invert the satellite regional gravity anomaly data with 10 km interval in x -axis and y -axis for the Sichuan-Yunnan region, which has complex geological structures with a large number of major faults, and negative gravity anomalies varying from -540~-90 mGal. We applied the method to invert the Moho depth below this region using reference level 35.5 km and density contrast -0.63 g·cm -3 at the earth surface with attenuation coefficient 0.0018. We compared the result with receiver function from Li et al. (2014) and other geological information. The differences between results of receiver function and our method at most seismic stations are less than 6 km. Therefore the Moho discontinuation derived from this method shows good correlation with the results of receiver function, other prior geophysical and geological information. Density contrast interface inversion is one of the primary subjects in gravity field research for understanding the earth's interior structure. This work combines the merits of the parabolic density model and the algorithm in the frequency domain, and applies the parabolic density function to the Parker-Oldenburg forward modeling and inversion algorithm. The tests on synthetic data and real data prove the new approach is rapid and effective. By inverting gravity anomaly data using this new approach, we obtained the Moho depth distribution in the Sichuan-Yunnan area, which shows that the Moho interface is shallow in the southeast but deep in the northwest. The Longmen Shan fault zone is a transition zone of the Moho depth ranging from 42 km to 58 km.

1. Institute of Geophysics, China Earthquake Administration, Beijing 100081, China; 2. Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China; 3. CNPC Xibu Drilling Engineering Sulige Gas Field Development, Ordos Uxin Qi 017300, China

密度界面反演作为了解地球内部结构的一种重要方法,长期以来都是重力学研究的主要内容.本文结合抛物线密度模型及频率域算法的优点,将抛物线密度函数应用于Parker-Oldenburg算法,经过理论推导得到了抛物线密度模型的频率域公式,从而建立了基于抛物线密度模型的三维密度界面重力异常正反演的算法和流程.理论模型数据试验表明本方法快速、有效,适用于大多数浅部比深部增加更快的实际地壳密度.研究中还利用该方法对川滇地区重力异常进行了反演,获得了该区的莫霍面深度分布,并与接收函数研究结果进行对比分析,进一步验证了本文方法的正确性和有效性.

... 张恩会等, 2015) ...

... 张恩会等, 2015), 在滇西地块内莫霍面自北向南逐渐变浅, 深度约38~52km, 而该区内由人工地震探测剖面(张恩会等, 2013 ...

2007

0.0

张智, 徐春明, 孟补在, 等. 2007. 洱源-江川宽角地震剖面的地壳反射特征[J]. 地球物理学报, 50(4): 1082-1088.

ZHANG

Zhi

, XU

Chun-ming

, MENG

Bu-zai

, et al. 2007. Crustal reflectivity characters from the Eryuan-Jiangchuan wide-angle seismic profile[J]. Chinese Journal of Geophysics, 50(4): 1082-1088(in Chinese).

By prestack migration processing to the wide angle reflection seismic data of the EryuanJiangchuan profile in Yunnan Province,we obtain a crustal reflectivity section which is similar to nearlyvertical incidence seismic data. Both the reflectivity image and the crustal velocity structure jointly demonstrate that the crustal thickness thins from about 45 km on the northwestern end of the profile to about 40 km on the southeastern end. Near the northwest of Eryuan and Chuxiong, there are a series of southeastdipping strong reflectors at depth 10 km and a series of northwestdipping strong reflection 50 km to its southwest. Crustal reflection attributes obviously differ on the both sides of the Yimen fault. To the northwest of the Yimen fault, two sets of reflectors with strong amplitude dipping upwards lie in the middlelower crust of depths 25～40 km, and are cut by the ChuxiongJianshui fault. To the southeast of Yimen fault, no obvious strong discontinuous reflection appears in the crust. This unique crustal velocity structure and reflectivity images are explained to be the results of thickening and deformation of crust under the joint action of Indian plates eastward subduction and eastwar escape of the crustal material at the eastern margin of Tibet.

1 Department of Resource and Environment Engineering, Guilin Institute of Technology, Guilin 541004, China 2 College of Geoexploration Science and Technology, Jilin University, Changchun 130026, China3 State Key Laboratory of Lithospheric Tectonic Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China4 Liaoning Seismological Bureau, Shenyang 110031, China

通过对洱源-江川宽角反射地震资料的叠前偏移处理成像，得到了一个类似于近垂直入射多道地震数据的记录剖面.反射剖面图像与地壳速度结构共同揭示出地壳厚度由剖面西北端(约45 km)向东南端(约40 km)减薄.在洱源-楚雄西北附近深度约10 km处存在一组向东南倾斜的强反射震相，其东南约50 km处存在向西北倾斜的强射震相.易门断裂两侧地壳反射属性具有明显的差异，易门断裂之西北方向深度25～40 km处，中下地壳内存在两组强振幅，向东南方向上倾的地震反射同相轴，并被楚雄-建水断裂后期所错断，易门断裂之东南方向上，地壳内反射较为均一，未见特别明显的强间断面反射信息，这个反射结构被解释为印度板块东向俯冲与藏东缘地壳物质东向逃逸综合作用导致下地壳增厚和厚地壳变形的结果.

... 张智等, 2007 ...

2005

0.0

... 钟锴等, 2005 ...

2003

0.0

... 周光全等, 2003 ...

2003

0.0

... 575i2计算莫霍界面上、下密度差(Christensen et al ...

1986

0.0

... , 1982)、连续变形模型(England et al ...

1974

0.0

... 2 反演在重力界面反演方法中, 基于频率域的Parker迭代界面反演方法(Oldenburg, 1974), 由于适应性强、计算速度快, 得到了广泛的应用 ...

1997

0.0

... , 1986)和下地壳流模式(Royden et al ...

1982

0.0

... 模型(Tapponnier et al ...