2020年7月22日阿拉斯加7.8级地震同震电离层扰动分析

Analysis of coseismic ionospheric disturbance of Alaska M 7.8 earthquake on July 22,2020

利用全球导航卫星系统(GNSS)、电离层测高仪和地震仪数据,从振幅及波形、时空分布、传播速度与方向、时频域等角度对2020年阿拉斯加7.8级地震同震电离层扰动(Co-seismic ionospheric disturbances,CIDs)特性进行探究.卫星G03、G04和G09在地震西部探测到3类CIDs,最大扰动幅度约0.1 TECU (1 TECU=10^(16) el/m~2),并且均沿着地震断层破裂延伸方向(西南方向)传播;而在地震北部与东部未发现CIDs.根据CIDs的速度及中心频率将其分为三类,第一类为高速传播的CIDs(速度约为2.93 km·s^(-1)),中心频率约11 mHz,符合瑞利波激发的电离层扰动特征;第二类CIDs的传播速度约为1.69 km·s^(-1)和1.55 km·s^(-1),中心频率约4.5 mHz和4.7 mHz,符合声波引起的电离层扰动频率;第三类CIDs速度约为0.98 km·s^(-1)和1.11 km·s^(-1),中心频率约2.9 mHz,可能为声波引起的另一类电离层扰动.同时,利用CIDs时空数据估计的CIDs扰动源位置与震中较为接近,进一步说明电离层扰动由地震激发.通过对GNSS站及地震仪位移的分析,估计了地震瑞利波沿西南方向传播速度与第一类CIDs较为吻合,验证了第一类CIDs由瑞利波激发,且断层的垂直位移是引起电离层扰动的重要因素.测高仪观测到电离层临界频率(f_(0)F_(2))发生显著波动,探测到CIDs的传播速度约1.02 km·s^(-1),传播速度和方向与卫星G03、G04探测的CIDs较为吻合,推断其属于第三类CIDs.

The characteristics of co-seismic ionospheric disturbances(CIDs) of the 2020 Alaska M_W7.8 earthquake were explored.Using GNSS,ionosonde and seismograph data,we discussed from multiple perspectives of amplitude and waveform,spatiotemporal distribution,propagation velocity and direction,and time-frequency domain.The satellites G03,G04 and G09 detected three types of CIDs in the west of the earthquake,with a maximum disturbance amplitude of about 0.1 TECU(1 TECU=10~(16) el/m~2),and all propagated along the extension direction of the earthquake fault rupture(southwest direction);however,no CIDs were found in the north and east of the earthquake.The CIDs are divided into three types according to their velocity and center frequency.The first type is the CIDs with high-velocity propagation(the velocity is about 2.93 km·s~(-1)),and the center frequency is about 11 mHz,which is consistent with the ionospheric disturbance characteristics excited by Rayleigh waves.The second type of the CIDs had the propagation velocities of about 1.69 km·s~(-1) and 1.55 km·s~(-1),and their center frequencies are about 4.5 mHz and 4.7 mHz,which are consistent with the ionospheric disturbance frequencies caused by sound waves.The third type of the CIDs had the propagation velocities of about 0.98 km·s~(-1) and 1.11 km·s~(-1),and the center frequency is about 2.9 mHz,The third type of CIDs may be another type of ionospheric disturbance caused by acoustic waves.Meanwhile,the location of the CIDs source estimated by the CIDs spatiotemporal data is very close to the epicenter,which further indicates that the ionospheric disturbance is excited by earthquakes.By analyzing the displacements of GNSS stations and seismographs,it is estimated that the propagation velocity of seismic Rayleigh waves in the southwest direction is in good agreement with the first type of CIDs.It is verified that the first type of CIDs is excited by Rayleigh waves,and the vertical displacement of the fault is an important factor causing the ionospheric disturbance.The peak frequency of F2 layer(f_0F_2) observed by ionosonde fluctuates significantly,and the propagation velocity of the detected CIDs is about 1.02 km·s~(-1).The propagation velocity and direction are in good agreement with the CIDs detected by the satellites G03 and G04,therefore it is inferred that it belongs to the third type of CIDs.