Anomaly of the ionospheric electron density close to earthquakes: Case studies of Pu’er and Wenchuan earthquakes

The electron density recorded onboard the DEMETER satellite was analyzed to search for possible anomalies before earthquakes both in space and time. To distinguish pre-earthquake anomalies from the other anomalies related to geomagnetic activity, data were filtered using the Kp index. The analysis is based on the comparison of data recorded closely to earthquakes in space and time and past data for the same area. In analyzing data around the time and location of the Pu’er and Wenchuan earthquakes, obvious anomalies in electron density were found close to the epicenters, and some remarkable disturbances were detected before the earthquakes occurred. The results were finally compared with those of previous works that used the same data but employed different analysis methods. Good agreement was found which suggests that these anomalies have a close relation to the earthquake preparation.