南北地震带北段地壳波速变化的成像研究

发布时间：2018-02-25 17:36

本文关键词： 背景噪声层析成像速度结构 2013年岷县漳县地震 2016年青海门源地震南北地震带北段　出处：《中国地震局兰州地震研究所》2017年硕士论文　论文类型：学位论文

【摘要】：地震预报是当代自然科学领域里一个难度很大且富有魅力的前沿课题。近年来,随着地震预测相关问题的深入研究,发现地震参数的精确测定是一个关键问题,其结果对于地震预测有着非常重要的作用。伴随着信息化与大数据的发展,现代数字地震记录优点被进一步放大,频带宽、动态范围大、分辨率高等优点逐渐为测定新的地震参数、介质参数与深入研究地震发生的构造环境和震源特征提供了无限的可能,为地震预报研究的深入和预报水平的提高带来了新的希望。南北地震带北段是我国主要的中强地震频发区,每次中强地震前后地下介质的物理属性,包括弹塑性、相变、密度等或多或少会发生一定的变化,介质属性的变化一定会导致震源区波速的变化。因此本文利用背景噪声方法研究了南北地震带北段的成像特征,得到了Rayleigh面波6-60s的相速度成像图;分析了2013年岷县漳县Ms6.6地震以及2016年门源Ms6.4地震前后波速的变化特征。得到以下初步结论:(1)南北地震带北段速度分布主要与块体分布较为一致,整个南北地震带北段大部分区域处于低速状态,整个速度分布存在极大的横向不均匀性,速度分布东西较为明显,结果大致以祁连山断裂带为分界线,西南为低速区域,北东为高速区域。可能与南北地震带北段地壳厚度结构和沉积层有关:西向东减薄、南北向较为均匀。此结果与该区域布格重力异常值由西向东增大、走向主要为北北西和近南北向展布相似。(2)南北地震带北段的2011-2016年的动态波速演化历程表明了南北地震带北段的应力与能量积累过程。不同周期的成像结果较为一致,整个南北地震带活动性较强,波速变化较为明显,波速变化最大在0.007%,不同区域变化幅度差异性较大。陇西块体,华南块体以及柴达木块体都出现了波速降低;阿拉善块体则有明显的波速升高,正好处于震中附近,可以发现波速的波动性。(3)2013年岷县漳县Ms6.6地震前后出现了较为明显的波速异常,地震后在震源区西北与东南方向出现了Rayleigh面波群速度的降低,西南侧则出现了速度的升高,使得地震震中正好位于该异常区域低速与高速的转换带,属于高低速异常的过渡区域,一般高低速转换带处于活动地块边界,绝大部分大地震都发生在这种边界的活动构造带上。因为一般而言,低速区是地壳容易发生形变的区域,高速区边界容易发生应力的集中。(4)成像结果显示2016年01月21日青海门源县(101.62°E,37.68°N)Ms6.4地震在T=10s时,震源区出现了明显的波速降低,异常区域横跨冷龙岭断裂带;在T=12s,14s与16s时,震源区南部即祁连块体出现波速降低;震源区的北侧则出现了不明显的速度升高,在地震发生前,可能是断裂带内及其周边区域应力逐渐积累,波速也逐渐增加,震源区的北侧有可能是此次地震区域应力积累的区域。因为其北侧与东侧是刚性的戈壁-阿拉善地块和鄂尔多斯地块,受到了一定的阻挡。震后成像结果显示,在T=10s,12s和14s时,震后三个月内震源西侧波速明显降低,从周期10-14s速度降低区域逐渐增大,祁连块体与柴达木块体均处于速度降低区域;在震源区东侧有不明显的速度升高,可能是应力与能量向东迁移。根据Rayleigh面波波速的演化历程,从一定的程度上面反应出此次地震能量的积累与释放过程。在漫长的地质构造运动的进程中,天然地震是构造活动的结果,后期的地震活动是前期地震活动的继续。通过分析现行的地震活动,通过一系列的反演可以反映构造活动的规模、地壳深处应力分布状况及可能的应力集中部位,对于地震分析预测研究具有重要的意义。
[Abstract]:Earthquake prediction is a very difficult and attractive topic in contemporary natural science field. In recent years, with the in-depth study of issues related to earthquake prediction, found the precise determination of earthquake parameters is a key problem, the results for earthquake prediction plays a very important role. With the development of information and data. Modern digital seismic records has been further enlarged, wide frequency band, large dynamic range, high resolution gradually for the determination of earthquake parameters of medium and deep research on the tectonic environment of the earthquake parameters and source characteristics provides unlimited possibilities, brings new hope for earthquake prediction research and raise the level of forecast. North and south the seismic belt of strong earthquakes in China main prone areas, physical properties before and after strong earthquakes each underground medium, including elastic-plastic, phase transition, density or more Or less change, change will lead to changes in media properties. In this paper the velocity source region is studied using the imaging features of the northern section of the North South seismic belt method of background noise, the phase velocity of surface wave imaging Rayleigh 6-60s; analysis of the 2013 Ms6.6 earthquake and Minxian Zhang county before and after the 2016 Ms6.4 earthquake wave gate the change of characteristics. The following conclusions: (1) northern section of North South seismic belt velocity distribution is consistent with the distribution of the main block, the northern most areas of the North South seismic belt in low speed state, the velocity distribution has great lateral inhomogeneity, the velocity distribution of things is more obvious, the results in the Qilian Mountains fault zone as a boundary for the low speed region, southwest, North East high speed area. And northern section of North South seismic belt of crustal thickness and sedimentary structure: West to east to the north and south is thinning. Uniform. This result with the regional Bouguer gravity anomaly value increases from west to East, mainly to NNW and nearly north-south distribution. (2) the dynamic wave velocity of 2011-2016 years of the northern section of North South seismic belt evolution shows that the northern section of North South Seismic Belt should be the process of accumulation of force and energy. Consistent imaging in different periods the whole activity of the North South seismic belt velocity is stronger, the more obvious changes, the biggest change in the 0.007% wave velocity, amplitude change in different regions of difference. Longxi block, Southern China block and Qaidam block body appeared wave speed of Alashan block; there is a substantial increase in velocity, just near the epicenter can be found. Fluctuation velocity. (3) before and after the 2013 Minxian Ms6.6 earthquake wave appeared Zhangxian obvious anomalies after the earthquake in the northwest and southeast direction of focal region appears to reduce Rayleigh surface wave group velocity, The southwest side appeared in the speed increases, the earthquake epicenter is located in the abnormal regions of low speed and high speed conversion with high speed, belonging to the transition region of anomalies, the general high speed conversion belt in the block boundary, most large earthquakes occur in the boundary of the active tectonic belt. Generally speaking, the low velocity zone it is easier to deform the crust area, high-speed zone boundary is prone to stress concentration. (4) the imaging results show that in 2016 01 in Qinghai on 21 September Menyuan County (101.62 ~ E, 37.68 ~ N) in the T=10s Ms6.4 earthquake, the focal region appeared apparent wave velocity decreased, the abnormal region across Lenglongling fault zone in T=12s, 14s and 16S; when the southern source area that Qilian block appears on the north side of the wave speed; the focal region appeared obvious increase before the earthquake, may be in the fault zone and its surrounding area of stress accumulation, The wave velocity increases gradually, the North source region may be the earthquake regional stress accumulation area. Because of the north and east of the Gobi - Alashan block is rigid and Erdos plots, by a certain barrier. After the imaging results showed that in T=10s, 12s and 14s, three months after the earthquake in the west of seismic wave velocity from the cycle of 10-14s decreased significantly, reduced speed area gradually increased, Qilian block and Qaidam block body are at reduced speed in the East region; source region is not obvious increase may be the transfer of force and energy to the East. According to the evolution of the Rayleigh surface wave velocity, from a certain extent above reaction process with the release of the seismic energy accumulation. In the long process of geological tectonic movement, earthquake tectonic activities are the result of seismic activity of the latter is to pre earthquake activity. Through the analysis of the current Seismicity can reflect the scale of tectonic activities through a series of inversion. The stress distribution and the possible location of stress concentration in the earth's crust are of great significance for earthquake prediction.

【学位授予单位】：中国地震局兰州地震研究所
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P315

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