利用GPS和DEMETER数据分析汶川地震前电离层变化

摘要

Based on GPS TEC data and ISL detector data recorded by the French DEMETER satellite, ionospheric perturbations before the Wenchuan earthquake were analyzed. It is found that GPS TEC above the epicenter continuously decreased in the afternoon period during 6 May to 10 May but increased in the afternoon of 9 May. The spatial distribution of the TEC anomaly mainly located in the south of the epicenter, and the size of perturbation area was 1 100-1 670km and 1 600 ~3 700km from the epicenter in the latitudinal and longitudinal directions, respectively. It is further found that negative anomaly area located southeast on 6 May and moved to southwest on 7 May from epicenter. On 9 May, the anomaly turned to be positive and occurred in the southeast of the epicenter. The intensity of negative anomaly in the southwest or south area from epicenter was stronger than that in the southeast area, compared with the southwest area, the intensity of positive anomaly in southeast or south area was stronger. Moreover, it could be seen that the perturbation was also observed in the geomagnetic conjugate points of epicenter at the southern hemisphere. In addition .contour analysis on ionopheric plasma shows that electron density ( Ne ) and ion density ( Ni) also reduced during 6 to 10 May. The anomalous distribution was in good conformity with TEC, which was concentrated mainly in the south of epicenter. There were two negative anomaly peaks along the earthquake longitude, which were symmetrical about the magnetic equator. Base on the above observation, we finally discuss the physical mechanism of the seismoionospheric anomaly according to Lithosphere-Atmosphere-Ionosphere Couling( LAIC ) model.%利用GPS TEC和法国DEMETER卫星ISL探测器的观测数据,分析了汶川地震前电离层变化.结果表明,电离层TEC在5月6-10日地方时下午有连续的负异常现象,5月9日地方时下午有明显的正异常现象.电离层TEC异常的范围主要位于震中南部区域,EW方向上1 100 ～1 670km,SN方向上1 600 ～3 700km.5月6日的负异常偏震中东南,5月7日的负异常偏震中西南,5月9日的正异常偏震中东南.震中西南和南部地区负异常较东南地区明显,震中南部和东南地区正异常程度较西南地区偏高,震中位置所对应南半球磁力线共轭区都出现了一定程度的正或负扰动.DEMETER卫星观测的电子密度Ne和离子密度N.在5月6-10日也出现了明显的负异常,异常分布与电离层TEC异常分布较为一致,主要集中在震中南部.震中所在的经度带上存在2个负异常峰值,且在纬度上关于地磁赤道对称.最后在上述异常的基础上,对基于岩石圈-大气层-电离层耦合的地震电离层异常机理开展了初步讨论.