红河断裂带域壳幔地震各向异性与深部物质迁移

In eastern Himalayan syntaxis, strong tectonism makes regional stress direction change clockwise, form the tectonic unit of eastward extrusion of Tibetan plateau: Sichuan-Yunnan block. There are many large strike-slip faults and large historic earthquakes in this region, where distribute rich metallogenic belts and furthermore passageway of Tibetan plateau material escape southeastward. Honghe fault is the southwest boundary of Sichuan-Yunnan block, as well as the tectonic boundary of first- order block in Chinese mainland. ..The project will set up temporary seismic array across the fault, with the data from permanent seismic stations and other temporary observations, and study seismic anisotropy beneath Honghe fault zone. Combining with surface deformation, fault activity, seismic anisotropy, velocity structure, discontinuity change and other geophysical data, this project will discuss and obtain comprehensive research results along Honghe fault zone, from surface to upper mantle, from local fault to regional background. ..The project adopts multiple analysis techniques including body wave anisotropy with advantage of lateral resolution and surface wave anisotropy with advantage of vertical resolution. It will obtain 3D distribution of seismic anisotropy beneath Honghe fault zone. Also, it will obtain 3D velocity structure combining with other inversion results. The project will study crustal flow and mantle flow shape beneath Honghe fault zone, discuss deep material migration and its deep tectonic implications to activity of large earthquakes and metallogenic belts.

在喜马拉雅东构造结，强烈的构造作用造成应力场方向发生顺时针方向旋转，形成青藏高原向东挤出的构造单元 — 川滇块体。该区域发育了系列大型走滑断裂带和强烈的大地震活动，聚集了丰富的成矿带，更是青藏高原物质向东南逃逸的通道。红河断裂带是川滇块体西南侧边界和一级块体的构造边界。项目计划布设跨断裂带流动地震台阵，结合区域固定地震台网和其他流动观测资料，重点通过开展红河断裂带域地震各向异性研究。结合地表形变、断裂活动性、各向异性、速度结构与壳幔界面变化及其他地球物理资料的综合讨论，形成由地表到上地幔，由局部断裂到区域背景的研究结果。项目采用具有横向分辨优势的体波各向异性和垂向分辨优势的面波各向异性多种分析技术，获得各向异性三维分布。结合其他反演结果，还将获得区域三维速度分布图像。项目将研究红河断裂带域的地壳流和地幔流动形态，探讨红河断裂带域深部物质迁移及其对大地震活动及成矿的深部构造含义。

项目完成了跨红河断裂带的宽频带流动地震台阵测线，布设了一个跨红河断裂的小型GNSS台阵测线。在红河断裂东南段开挖了探槽，揭示红河断裂南段为全新世活动断裂。GNSS数据表明，红河断裂西北端部（与丽江-小金河断裂交汇）剪切应变率高、拉张为主，断裂东南段（与小江断裂交汇区域）也是高剪切应变率，但红河断裂中段剪切应变率接近于零，表明断裂活动处于闭锁状态。..红河断裂带下方的岩石圈S波速度结构显示，断裂带下方岩石圈速度强烈变化。远震S波分裂数据揭示壳幔方位各向异性有一条明显的26º20′N分界线，北侧快波方向近NS，南侧快波方向为EW，揭示南侧EW走向的快波方向起源于上地幔。..红河断裂带西北端部地震测线数据显示，地壳厚度自西向东缓慢变深，程海断裂以东呈现双层重叠结构。地壳各向异性显示，快波方向平行断裂走向，断裂下方的各向异性强度明显高于断裂两侧。断裂带中南段测线数据显示，断裂带西侧地壳各向异性快波方向比较一致，但断裂带附近各向异性更强。岩石圈各向异性也显示红河断裂有明显扰动。上地壳各向异性显示，红河断裂带西北端部，从西到东，快S波方向呈现NNW到NS到NNE顺时针变化特征，断裂带与丽江-小金河断裂交汇区的时间延迟较大，揭示了强烈变形。断裂带中南段，显示断裂附近快S方向平行于断裂走向。断裂带中段地壳可能形成了垂向变形一致的区域，红河断裂带有强烈的控制作用。..基于密集台阵背景噪声记录，得到红河断裂带域S波3D速度结构和方位各向异性。断裂带西北段，中上地壳深度范围低速物质从丽江-小金河断裂西段往西越过红河断裂之后停止；快波方向由上地壳的近N-S向变为中下地壳的NW-SE向。红河断裂带中南段，两侧S波速度显著差异；小江断裂带中下地壳低速物质南下，被红河断裂带阻挡。..综合研究表明，红河断裂带可分为三段。西北和东南段区域地震危险性较强，中段则显示高度闭锁。