利用中国GPS站网对地震波引发的大尺度电离层扰动的观测

Imaging of the large-scale ionospheric disturbances induced by seismic waves using GPS network in China

地震瑞利波在沿地表传输时衰减很慢,其能量在远离震中的区域仍然能够激发大气和电离层扰动.本文利用中国境内的GPS接收机网络观测电离层总电子含量(total electron content,TEC),分析了2011年日本地震后在中国区域上空产生的电离层扰动.研究发现,瑞利波的能量从地面经大气耦合传输到电离层高度,导致在中国区域上空电离层出现与瑞利波传播同步的TEC扰动.利用中东部的稠密接收机网络,还揭示了扰动的大尺度二维空间结构:瑞利波经过后产生的TEC扰动呈条带状,在中纬度地区沿西北—东南方向排列,而在低纬度大致为东西方向.条带的转向可能与地磁场作用下的中性-离子耦合过程有关,大气波动导致的等离子扰动倾向于沿磁力线方向(向南)传播,从而形成垂直磁力线方向(东西)的波前结构.这是首次在远离震中的区域使用GPS站网研究地震波耦合电离层扰动的大尺度二维空间结构.

Rayleigh waves travel along the Earth′s surface,with vertical ground displacements to excite far field disturbances in the atmosphere and ionosphere.This study uses massive total electron content(TEC)data from the GPS receiver network in China to portray the ionospheric disturbances after the 2011 Tohoku earthquake.The results reveal that,the Rayleigh waves reach far field and the energy propagates upward into the ionosphere through the lithosphere-atmosphere-ionosphere coupling,hence causes large-scale TEC disturbances over China.With dense network in central and eastern China,two-dimensional maps of the TEC disturbances are achieved,showing large-scale zonal band structures.The wave fronts are oriented in the northwest-southeast direction at mid-latitude,then rotate to east-west at lower latitudes.The rotation is expected due to the neutral-ion coupling,which effectively drives plasma motion along geomagnetic field lines in favor of southward propagation of the ionospheric disturbances.This is the first two-dimensional imaging of large-scale seismo-ionospheric disturbances caused by far field Rayleigh waves.