2015年尼泊尔地震的震前电离层异常探测

Abstract

提出了一种基于奇异谱分析的电离层异常探测的方法。通过对尼泊尔地震震中周围GIM格网点TEC时间序列的探测，发现在2015年4月23日震中东部区域出现电离层正异常。进一步利用二维电离层地图分析异常空间分布，发现出现电离层正异常的区域为25°N-37.5°N，90°E-110°E，时间为2015年4月23日UT9:00-15:00。利用中国陆态网数据计算异常区域卫星穿刺点轨迹STEC变化情况，发现2015年4月23日穿刺点轨迹进入异常区域后STEC值比前后几天明显增大，而离开异常区域后又恢复正常。采用CIT(computerized ionosphere tomography)方法详细地呈现了电离层异常的三维形态，发现4月23日UT9:00-15:00在震中东部区域出现电离层正异常，峰值位于约30°N，115°E，高度范围为100~500 km，且异常峰值随高度变化与电离层本身垂直密度分布规律相一致。

Alternate abstract:

An ionospheric anomaly detection method based on singular spectrum analysis is introduced firstly.With the TEC time sequence of GIM grid points around the Nepal earthquake epicenter, the positive ionospheric anomalies are determined on 23 April around the eastern region of the epicenter. Using the two-dimensional ionospheric anomalies map, further analysis is taken to comfirm the ionospheric positive anomaly area distributing from 25°N to 37.5°N, 90°E to 110°E, and the anomaly time ranging UT9:00 to UT15:00 on 23 April, 2015. The data of crustal movement observation network of China issued to analyze the STEC fluctuation changes of IPP(ionosphere piece piont) trajectories in the abnormal area, and it is found that on 23 April the STEC values of IPP trajectories passing through the abnormal area are obviously larger than the ones a few days after and before the earthquake time, and returned to the normal level after leaving the abnormal area. Lastly, the CIT (computerized ionosphere tomography) method is used to present the 3D ionospheric anomalies distribution, and it is found that, at UT9:00-UT15:00 on 23 April the peak of ionospheric positive anomaly on the eastern region of the epicenter is approximately at (30°N, 115°E), with the altitude ranging from 100 to 500 km. Also the anomalous peak varies with height is consistent with ionosphere density vertical distribution.