用跨断层形变资料分析鲜水河断裂西北段的运动特征

本文利用主成分分析、震间位错反演和小波技术分析了鲜水河断裂西北段的跨断层形变资料(1986—2013).结果表明:以左旋走滑为主的断层长期运动为跨断层资料的主要信息,且符合负指数函数的运动规律,随着断层深度的增加,滑动量逐渐减弱.从炉霍段、道孚段到乾宁段,断层闭锁程度逐渐增强.2001年昆仑山M8.1地震发生后,鲜水河断裂西北段地壳浅层(地表以下30 km)的左旋走滑明显减弱,到2013年的累积减弱量为3~13 mm.5·12汶川M8.0地震发生前,断层滑动出现周期4~5年的增强信号.4·20芦山M7.0地震发生前,断层滑动首先出现低频信号(4~5年周期)增强,随着地震发生临近,强信号频率逐渐升高,直到出现周期为1年的强信号.

Movement characteristics of the northwest segment of the Xianshuihe fault zone derived from cross-fault deformation data

Cross-fault deformation data are affected by many factors, which makes analysis of such data difficult. This paper attempts to separate information of tectonic movements and non-tectonic movements, and quantity the effect of major earthquakes in near and far fields.This work used the PCAIM (principal component analysis-based inversion method), developed by California Institute of Technology, to recover the time-evolution history of the source of surface deformation using the cross-fault deformation data (1986—2013) from the northwestern Xianshuihe fault zone. We improved the PCAIM using genetic algorithm to search the global optimal solution, and analyzed the spectral characteristics of PCA (Principal Component Analysis) time coefficients by complex wavelet transform. Ultimately we obtained the time-frequency correlation between the main components and tectonic movements.The first principal component (contribution rate: 68.8%) shows that the main information of cross-fault data is long-term movement of the fault with sinistral strike-slip, in accordance with the movement rule of negative exponential function (TC=0.4546－0.6539e^－0.0018t), and the slip rate declined gradually with the increase of depth. The fault locking becomes stronger from Luhuo, Daofu, to Qianning. The western part of the Luhuo segment (west of Luoqiu) is not locked at 40 km depth, while other fault segments locked at 20~30 km depth, and the eastern part of the Qianning segment (east of Longdeng) locked on the Earth's surface. The second principal component (contribution rate: 5.9%) shows that in the northwest segment of the Xianshuihe fault, the slip rate of the shallow crust (30 km below the surface) decreased by 3~13 mm in 2013 after the Kunlun Mountains M8.1 earthquake of 2001. The third principal component (contribution rate: 3.6%) indicates that before the Wenchuan M8.0 earthquake of 2008, the fault slip exhibited stronger signal of a 4~5 year cycle. Before the Lushan M7.0 earthquake of 2013, the stronger low frequency signal (4~5 year cycle) appeared firstly in the fault slip, then transferred to the higher frequency signal. With approaching of the earthquake, the frequency of signal increased gradually, till the stronger signal of 1-year cycle occurred.We obtained better results by analysis of cross-fault data using principal component analysis, interseismic dislocation inversion and wavelet technology. It allows us to identify long-term movement of faults, the impact of major earthquakes on faults and possible short- and medium-term earthquake precursors.