中文摘要：

本文通过CODE提供的全球范围GIM格网电离层TEC数据,针对2015年4月20日花莲M_W6.4级地震,在尽可能排除太阳和地磁活动等干扰因素后,借助滑动四分位距法,以震前27天同一时刻的观测值为背景值,判别与地震有关的电离层异常信息.分析结果显示：花莲地震前TEC出现明显正异常,排除来自太阳和地磁活动因素的影响,震前17天的TEC正异常在很大程度上与花莲地震有关;震前TEC异常表现为自东向西移动,并消失在西部,且异常区形态呈现共轭结构,共轭区与震中附近异常状况变化趋势大致相同;本次异常的峰值点不在震中正上方,而是接近震中偏向高纬方向;震前17天震中的电离层TEC异常持续时间十余小时,异常持续时间是否与临震时间及地方时相关还有待对比总结.

英文摘要：

Taiwan is located on a seismically earthquake zone. At 09：42 local time （01：42UTC） on April 20, 2015, an Mw 6.4 earthquake struck Hualieu County in Taiwan Province. The earthquake struck at a depth of around 7km, and the quake could be possibly felt throughout the island. News reports indicate that one person was killed in this earthquake. The ionospheric anomalies associated with earthquake were analyzed, on the basis of GIM global grid ionospheric data provided herein by the CODE. This project is performed by dint of the sliding quartile-based process, namely, we calculate the median data of continuous 27 days＇ observed TEC at each time in order to calculate the deviate deflection between the median and the 28th day＇ observed TEC. To investigate the relationship between ionospheric anomalies and Hualien earthquake, the possible confounding factors, such as solar and geomagnetic activity, should be excluded. The results show that positive TEC anomalies emerge obviously before Hualien earthquake, to the exclusion of the spatial factors, the positive TEC anomalies of 17th day before the earthquake have greater relevance with Hualien earthquake. Meanwhile, the TEC anomalies move from east to west, and disappear in the west. Conjugate structure is presented in the region of TEC anomalies in this earthquake; moreover, the conjugate region is similar to that of the abnormal situation near the epicenter. The anomaly peak is not directly above the epicenter, but appears on the north of the epicenter. Such results show that there is a good agreement between the analysis and previous research results. In addition, the TEC anomalies of 17th day before the earthquake last more than ten hours. In conclusion, preliminary study suggests that the TEC anomalies possibly related to Hualien earthquake, and whether the abnormal duration is related to the days prior to earthquake and local time is still need to be analyzed.