The Research On Ionospheric Anomalies Before Earthquake Based On GPS

The ionosphere is an important part of the earth's atmosphere,in early nineteenth century,humans have carried out research on the ionosphere,and found the ionospheric disturbance when the Alaskan earthquake occurred in 1960 s,this discovery provides a new research direction for earthquake precursors.The ionosphere is extremely easy to be influenced by solar activity and geomagnetic storm.In addition,the mechanism of pre-seismic ionospheric response is short of the support of systematic theory and powerful experiments.All of them compel the field of pre-seismic ionospheric response to face a huge controversy and challenge.With the occurrence of global violent earthquakes frequently and the rapid development of ionosphere sounding technology such as GPS in recent years,the research on pre-seismic ionospheric response has been a new hot spot in the research of earthquake precursor.The main aims of this work are to improve the shortcomings existing in the research on pre-seismic ionospheric response by using GPS along with other ionospheric sounding techniques.The specific research work and results are as follows:1)To the research on the ionospheric precursor under the unquiet state of the ionospheric weather before earthquake,the Mw7.1 Hector Mine earthquake,occurred in 1999,is taken as a research object.To discriminate ionospheric disturbance factors over the earthquake zone,the first thing was to employ the sliding interquartile range method which has been selected running background values with conditions to detect VTEC time series of monitoring point A(35°N,115°W)near the epicenter and reference point B(35°N,100°W)and point C(35°N,65°E)which are similar to point A in geomagnetic latitude.Secondly,to further clarify the ionospheric disturbance factors,IRI2012 model was used to study comparatively the VTEC anomalies of Point A,and a regional variability index is proposed.Thirdly,the global ionosphere maps(GIMs)and electron density profiles corresponding to abnormal moments were also detected.It is possible for ionospheric anomalies over the earthquake zone on October 14 th and 16 th to be caused by geomagnetic storm and seismic activity together,but affected by the seismic activity weakly.2)To the research on the ionospheric precursor under the quiet state of the ionosphericweather before earthquake,the Mw7.2 Mexico earthquake in 2010 is taken as a research object.A combined spatial-temporal analysis for ionospheric anomalies is proposed due to the difficulty whether pre-earthquake ionospheric anomalies over the earthquake zone are caused by the seismicity or not.Based on the approach above,the sliding interquartile range method was employed to detect VTEC time series of monitoring point A(32.5°N,115°W)near the epicenter and reference point B(32.5°N,100°W)and C(32.5°N,55°E)which are similar to point A in geomagnetic latitude.By detecting the Dst indexes,the influence of geomagnetic activity differences on the ionospheric anomaly detection was excluded.Combined with space weather conditions,the most likely abnormal period related to seismic activity has been achieved,and then spatial VTEC anomalies have also been successful extracted in the period of abnormal time above.Final research shows that positive anomalies over the earthquake preparation zone and its nearby on April 4 are related to the seismic activity and the VTEC anomalous peaks mainly concentrate in the east and south of the epicenter.3)In the study of ionospheric anomalies at impending earthquake moments,Mw8.8 Bio-Bio earthquake in Chile is taken as a research object in 2010.First of all,the observation data which from the IGS-SANT station near the epicenter was selected,then carrier phase smoothed code method was used to extract high precision TEC along the line of sight between satellite and station.At last,polynomial fitting method was used to detect TEC anomalies.It is found that TECs appeared positive and negative anomalies within 1 hour before earthquake.After the earthquake,the phenomena were happened which TECs appeared jitters.