基于GNSS基线变化的区域构造运动与应变特征提取

Extraction of regional tectonic movement and strain characteristics based on GNSS baselines variation

鉴于地壳形变具有高空间相关性的特点,以全球卫星导航系统(GNSS)观测网作为一个形变单元,基于三维无约束平差后的高精度基线向量,利用GNSS观测网络所有测站相互关联的基线向量方向与长度的变化主成分,来综合反映GNSS网形的变化,利用网形的变化提取区域高空间相关的构造形变信息,并提出利用高精度基线解算区域应变时间序列的方法。以日本境内长时间观测的国际GNSS服务(IGS)网络为例,解算了近13 a的基线时间序列,获取了2011年日本Mw9.0地震前后近、远场区域形变的时变特征,发现了近年来的多次强震,在震前数月的时间内均出现不同程度的非趋势性偏离,即稳定闭锁和反向加速的弧形转折变化特征,可能存在着应变的积累、释放与调整,与室内岩石破裂实验过程相吻合。同时,利用高精度的基线向量分别解算了近、远场区域应变动态变化时间序列,结果表明,多次强震前,均出现了不同程度的剪应变加速变化和面应变的释放-调整阶段,为区域地震危险性的判定提供了一条重要线索。

The characteristic of the high spatial dependence from the crustal deformation,regarding GNSS(Global Navigation Satellite System)network as a deformation observation unit,based on the high-precision baselines vectors obtained from three dimensional free network adjustment of GNSS network,we proposed a method of regional crustal deformation signals detection by the principal component of all the correlated baselines length and angles variation from the whole GNSS network.A method to calculate regional strain time series by using high precision baseline information is also proposed.Take the long-term IGS(International GNSS Service)observation network in Japan for example,we calculated the baselines time series for 13 years and obtained the dynamic evolution process of the crustal deformation before and after 2011≥Mw9.0 earthquake.The result shows that the obvious abnormal deviation appeared during a period of several months before the several earthquakes and the whole change curve is similar to parabola,which can be explained as the stability lock state and reverse acceleration process,suggesting the accumulation,release and adjustment.It agrees well with the deformation process of rock rupture experiment in the laboratory.Meantime,the high precision baseline vector is used to calculate the time series of regional strain dynamic variation in the near and far field respectively.The results show that the accelerated variation of shear strain and the release-adjustment stage of plane strain occur before many strong earthquakes,which maybe provide an important clue for the determination of seismic risk.