芦山M_s7.0地震前水平位移和同震水平位移研究
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摘要
本文利用"中国地壳运动观测网络(二期)"多个GPS连续观测站观测数据处理结果,将2013年4月20日四川芦山Ms7.0地震区域参考框架同震水平位移与全球参考框架同震水平位移进行比较,结果表明两组框架解一致,说明两种参考框架均可当作位错参考框架,也即全球参考框架同震水平位移也可视为区域参考框架同震水平位移.区域参考框架下GPS连续观测站地震前的水平位移和同震水平位移结果表明,震前数年,SCTQ站西侧的GPS站构造运动十分显著,而该站水平位移却很小,即出现反常的闭锁.但该站的同震水平位移使其弹性回跳至正常构造水平位移水平,因此SCTQ站震前的位移闭锁是水平位移空间分布中的异常,是芦山Ms7.0地震的前兆.水平位移时空变化表明,该站震前和震时位移完全符合里德的弹性回跳理论.区域参考框架中位移时间系列和同震水平位移的综合研究有助于对芦山地震地壳运动前兆的认识和解释.尽管本文未能直接采用其它GPS连续观测站的资料,但结合本文和其它研究结果可以证实,震中附近其它站地震前后的变化与SCTQ站类似.基于芦山地震前水平位移和同震水平位移及其与前兆关系的研究,本文进一步讨论了GPS监测网的布设、数据处理和分析等问题.
In this paper the coseismic horizontal displacements of the M_s7.0Lushan earthquake on April 20,2013 in Sichuan,China are obtained in the global and regional reference frames from continuous GPS observations at some stations in the Crustal Movement Observation Network of China(CMONOC)and other stations.Comparison of the two sets of solutions for the coseismic horizontal displacements shows that they are in good agreement and both of the reference frames can be taken as the dislocation reference frame for the coseismic horizontal displacements of this event.So the coseismic horizontal displacements in the global reference frame can be used as coseismic horizontal displacements in the regional reference frame.The relationship between the coseismic horizontal displacements and the preseismic horizontal displacements can be analyzed reasonably with the results in the regional reference frame so as to study the crustal movements precursory to this event.Time series of preseismic displacements and the coseismic displacements in the regional reference frame at continuous GPS observation stations show that the tectonic horizontal crustal movements were quite significant at some stations west to the station SCTQ near epicenter of the Lushan earthquake,while this station showed abnormal locking in the horizontal movement.The coseismic horizontal displacements at the station SCTQ and other stations were elastic rebound to their normal horizontal tectonic movements.Therefore the locked horizontal displacements at these stations were anomalous in the spatial distribution of the horizontal displacements at the GPS stations and were precursors to the earthquake.The horizontal displacement change in time and space show that the preseismic and coseismic displacements at the station SCTQ are in good agreement with Reid's elastic rebound model.The combined studies on time series of the horizontal displacements and the coseismic horizontal displacements in the regional reference frame are important for the reasonable explanation on the crustal movements precursory to the earthquake.Though the data used in this study are limited,combination of the results in this paper with other papers suggests that the result obtained from data at the station SCTQ can be verified by the data at other GPS stations.Based on the studies on the preseismic and coeseismic horizontal displacements,some problems in the GPS monitoring networks and the data processing and analyses are discussed.
引文
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