青藏高原东南缘的地壳应力场及其对壳幔变形的指示
发布时间：2018-07-23 09:18
【摘要】：喜马拉雅造山运动与青藏高原隆升是新生代以来世界上最大的地质事件之一。青藏高原受到印度板块碰撞挤压的影响,高原物质向东挤出,受稳定四川盆地的阻挡,这些物质转而向东南方向逃逸。地震的孕育与地壳的应力状态密切相关,其发生是在区域构造应力场作用下,周围的区域构造运动与震源区介质脆性变形相互作用的结果。对青藏高原东南缘地壳应力场的研究,能够帮助我们深入了解该地区的构造活动。本论文利用中国地震科学台阵探测项目(ChinArray)2011年8月到2103年12月在研究区的地震记录,采用gCAP的方法,反演了 239个地震事件(3.0 ≤ Mw ≤ 6.0)的震源机制解,并结合前人在该地区得到的447个震源机制解(合计686个),用阻尼线性反演的方法得到青藏高原东南缘的地壳应力场,并将应力场结果与GPS观测、SKS各向异性的结果作对比,进而探讨青藏高原东南缘的构造演化。青藏高原东南缘地震主要分布在5-15公里,地震沿主要断裂分布;震源机制解以走滑为主,但四川盆地西缘发育有大量的逆冲机制地震,云南西北部分布有拉张型地震;腾冲火山附近震源机制解类型比较复杂,这些地震不仅受主要断裂的控制,同时也受到火山活动的影响。总体上,青藏高原东南缘的地震主要受大的走滑断裂控制,而一些较小(Mw～3.0)的非走滑型地震事件受局部的构造活动控制。通过震源机制解反演,发现青藏高原东南缘的构造应力场以走滑为主,最大(σ1)和最小主应力轴(σ3)近水平;四川盆地西缘呈现挤压的应力状态,σ1近水平,σ3倾角较大(60°～80°);云南西北部呈现拉张的应力状态,其最小主应力轴σ3平行于活动断层的走向,σ1倾角较大,近垂直于地表。本文进一步由主应力轴计算出最大(SH)和最小水平应力(Sh)方位角,发现水平应力轴在26°N附近发生突变:在26°N以北,最大水平应力轴(SH)方向近E-W,最小水平应力轴(Sh)近S-N;在26°N以南,最大水平应力轴(SH)方向近S-N,最小水平应力轴(Sh)近E-W。此外,研究区最大水平应力(SH)整体上呈扇形展布,SH从腾冲火附近的NE-SW向向东逐渐转变为云南中部的近N-S向和云南东部的NW-SE向。同时最小水平应力(Sh)从腾冲火山以西的NW-SE向逐渐转变为云南中部的E-W向及云南东部的SW-NE 向。研究区最小水平主应力轴(Sh)和GPS地表位移反演得到的地壳最大应变方向一致,同时垂直于GPS地表位移方向和地形梯度的方向,说明川滇地区应力场的分布主要受重力势能和重力失稳的影响。SKS快波方向通常代表了地幔的最大形变方向,对比最小水平应力方向(最大应变方向)与SKS快波方向,发现在云南地区两者方向基本一致,表明云南地区地壳和地幔岩石圈的变形一致,因此云南地区地壳和上地幔可能是耦合的。
[Abstract]:Himalayan orogenic movement and uplift of Qinghai-Xizang Plateau are one of the biggest geological events in the world since the Cenozoic. The Qinghai-Xizang Plateau is affected by the collision and compression of the Indian plate, and the plateau material is squeezed eastward and blocked by the stable Sichuan basin. The earthquake preparation is closely related to the stress state of the earth's crust, and its occurrence is the result of the interaction between the regional tectonic movement around the earthquake and the brittle deformation of the medium in the focal area under the action of the regional tectonic stress field. The study of crustal stress field in the southeast margin of Qinghai-Xizang Plateau can help us to understand the tectonic activity in this area. In this paper, the focal mechanism solutions of 239 earthquake events (3.0 鈮，
本文编号：2138937
[Abstract]:Himalayan orogenic movement and uplift of Qinghai-Xizang Plateau are one of the biggest geological events in the world since the Cenozoic. The Qinghai-Xizang Plateau is affected by the collision and compression of the Indian plate, and the plateau material is squeezed eastward and blocked by the stable Sichuan basin. The earthquake preparation is closely related to the stress state of the earth's crust, and its occurrence is the result of the interaction between the regional tectonic movement around the earthquake and the brittle deformation of the medium in the focal area under the action of the regional tectonic stress field. The study of crustal stress field in the southeast margin of Qinghai-Xizang Plateau can help us to understand the tectonic activity in this area. In this paper, the focal mechanism solutions of 239 earthquake events (3.0 鈮，
本文编号：2138937
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