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۱VLF AND HF SEISMO–IONOSPHERIC ANOMALIES BEFORE THE 29 SEPT 2009 SAMOA EARTHQUAKE (MW = 8.1
نویسنده(ها): ، ،
اطلاعات انتشار: ششمین کنفرانس بین المللی زلزله شناسی و مهندسی زلزله، سال
تعداد صفحات: ۸
Using ICE (Instrument Champ Electrique) and IMSC (Instrument Magnetic Search Coil) experiments onboard the DEMETER (Detection of Electromagnetic Emissions Transmitted from Earthquake Regions) satellite we have surveyed possible variations in electromagnetic signals transmitted by the ground–based VLF transmitter NPM in Hawaii and in HF plasma waves close to the Samoa earthquake during the seismic activity. The indices Dst and Kp were used to distinguish pre–earthquake anomalies from the other anomalies related to the geomagnetic activities. The lack of significant geomagnetic activities indicates that these anomalous behaviors could be regarded as seismo–ionospheric precursors. It is also shown that comparative analysis is more effective in seismo–ionospheric studies.<\div>

۲DETECTED SEISMO–IONOSPHERIC ANOMALIES BEFORE STRONG EARTHQUAKES (M>6.0) USING DEMETER AND GPS DATA
نویسنده(ها): ، ،
اطلاعات انتشار: ششمین کنفرانس بین المللی زلزله شناسی و مهندسی زلزله، سال
تعداد صفحات: ۸
We have statistically analyzed the variations of the electron and ion densities to search for disturbances in the vicinity of Samoa earthquake prior to event using IAP (plasma analyzer) and ISL (Langmuir probe) experiments onboard DEMETER (Detection of Electromagnetic Emissions Transmitted from Earthquake Regions) satellite and GPS (Global Positioning System) measurements. The indices Dst and Kp were used to distinguish pre–earthquake anomalies from the other anomalies related to the geomagnetic activities. For studied case, a very good agreement was found between the different parameters estimated by DEMETER and GPS data in the detection of pre–seismic anomalies. The appearance of positive anomalies in both of DEMETER and TEC (Total Electron Content) data during 1 to 5 days before studied earthquake during quiet geomagnetic conditions indicates that these anomalous behaviors are highly regarded as seismo–ionospheric precursors.<\div>

۳DETECTION OF THE TEC SEISMO IONOSPHERIC ANOMALIES USING INTERQUARTILE, KALMAN FILTER AND WAVELET METHODS
نویسنده(ها): ،
اطلاعات انتشار: ششمین کنفرانس بین المللی زلزله شناسی و مهندسی زلزله، سال
تعداد صفحات: ۸
In this study, two datasets of Total Electron Content (TEC) time series have been analyzed to locate relevant anomalous variations in recent major Haiti and Samoa Islands earthquakes prior to the events. The duration of two datasets is 45 and 65 days for Haiti and Samoa Islands earthquakes respectively each at a time resolution of 2 hours. Since long time TEC signals are being used, the analysis excludes the abnormally looking background variations for Haiti and Samoa cases respectively without taking the sources into the considerations. However, some known sources such as solar terrestrial geomagnetic indices (i.e. Dst and Kp) have been used to avoid high natural perturbations which may mask pre–earthquake anomalies. As the first method, the interquartile method has been used to construct the higher and lower bounds in TEC data to detect disturbed states outside the bounds which might be associated with impending earthquakes. As another method, wavelet transformation has been applied on the two time series of TEC data to identify earthquake anomalies. Also in this study, Kalman filter has been applied in the detection process of prominent TEC anomalies related to earthquakes. A cross comparison of the different results concerning the methodology indicates that the interquartile method is capable of detecting the highest intensity anomaly values whereas Kalman filter method significantly detects more anomaly occurrences. All three methods detected a considerable number of anomalous occurrences during 1 to 15 days prior to the earthquakes in a period of low geomagnetic activities. The proposed method gets its credibility from the overall capabilities of the three integrated methods. In this regard, a good agreement in results was found between the different applied methods on TEC data in the detection of pre–seismic anomalies. The concurrency of the detected anomalous occurrences indicates that these anomalous behaviors are highly related to impending earthquakes.<\div>
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