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

TheelectrondensityrecordedonboardtheDEMETERsatellitewasanalyzedtosearchforpossibleanomaliesbeforeearthquakesbothinspaceandtime.Todistinguishpre-earthquakeanomaliesfromtheotheranomaliesrelatedtogeomagneticactivity,datawerefilteredusingtheK_pindex.Theanalysisisbasedonthecomparisonofdatarecordedcloselytoearthquakesinspaceandtimeandpastdataforthesamearea.InanalyzingdataaroundthetimeandlocationofthePu'erandWenchuanearthquakes,obviousanomaliesinelectrondensitywerefoundclosetotheepicenters,andsomeremarkabledisturbancesweredetectedbeforetheearthquakesoccurred.Theresultswerefinallycomparedwiththoseofpreviousworksthatusedthesamedatabutemployeddifferentanalysismethods.Goodagreementwasfoundwhichsuggeststhattheseanomalieshaveacloserelationtotheearthquakepreparation.