A Study On The Characteristics Of The Electron Density Variations Of Seismo-ionospheric Based On GPS And DEMETER Satellite Data

Recently, there are growing interests in studying the atmosphere-ionosphereresponse prior to earthquakes, including case studies and seismo-ionospheric couplingmechanism analysis. The existing studies have shown that many physical effects suchas piezomagnetism, piezoelectrics and pryromagnetic are associated with anearthquake, due to the extending of original microcrack and the development of theregenerate microcrack in the crust occurring in the earthquake preparation process.Consequently, some seismo-electromagnetic phenomena could then be observed byground based facilities and satellites within a certain range from the seismic source. Abrief list of such phenomena includes:①the phase or amplitude changes of theVLF/ELF/ULF signals,②total electron content (TEC) and critical frequency ofF2-layer (foF2) perturbations in ionosphere,③the anomalies in the electric field,magnetic field as well as plasma parameters,④thermal-infrared emission anomaly,⑤energetic particles bursts.Global Positioning System (GPS) measurement technique can be used fordetecting ionospheric response to earthquakes, in addition to investigating crustaldeformation characteristics and studying the motion of tectonic. Since the new century,several countries including Russia, USA, France and Ukraine have launched theirseismic electromagnetic satellites. Particularly, the scientific data of FranceDEMETER satellite are widely used to search for and characterize ionosphericperturbations associated with earthequakes. Now, the China Seismo-ElectromagneticSatellite (CSES) has been officially included in the national plans of satellite launch.This work focuses on the seismo-electromagnetic phenomena based on GPS andDEMETER satellite data. This thesis includes three parts. Firstly, it gives anintroduction about the principle of TEC measurement by GPS technique, theprocessing methods of satellite data as well as the ways to identify the abnormalsignals. Secondly, this thesis analyzes the observations of the multi-parameterseismo-ionospheric anomalies before the Wenchuan, Tohoku-oki and Yushuearthquake, respectively, and compares the characteristics of electron density variations before these three earthquakes. In addition, it presents the statisticalanalysis results of electron density perturbation before major earthquakes observed onDEMETER satellite and GPS measurements. Moreover, aiming to deepen theunderstanding of seismo-ionospheric phenomenon, it analyzes variations of totalelectron content (TEC) over southwest China during a period of low solar andgeomagnetic activity in April-October2008. Thirdly, it presents the research progressof modeling the ionospheric effect of the seismogenic electrostatic field (SEF) seen atthe earth’s surface as a perturbation of the vertical atmospheric electrostatic field inthe earthquake preparation zone.The main results of this work are as follows:1. Multi-parameter Seismo-ionospheric Anomalies Observation before the2008Wenchuan, China Mw7.9EarthquakeThis thesis analyzes the atmosphere-ionosphere response before2008Mw7.9Wenchuan earthquake based on GPS, DEMETER and NOAA/AVHRR satellite data.It is found that GPS TEC above the epicenter continuously decreased in the afternoonfrom6to10May but increased in the afternoon of9May. Contour analysis onionopheric plasma using ISL data onboard DEMETER satellite shows that electrondensity (Ne) and Ion density (Ni) also reduced from6to10May. The anomalousregions mainly lie in the south of epicenter, attesting to the anomalous TEC area. Thebrightness temperature (Tb) from NOAA/AVHRR data, calculated by the K indexmethod, shows a noticeable enhancement on the northwest side of the epicenter on7May, while Ion temperature (Ti) from DEMETER data increased on9May, with theamplitude of~12.5%. Besides, the energetic particle flux exhibited an obviouslyenhancement for the spectrum at100-600KeV energy range on6May. Preliminarystudy suggests the perturbations of these parameters (TEC, Ne, Ni, Tband Ti) beforethe Wenchuan earthquake may be related to the changes of vertical electric field in theatmosphere and ionosphere, induced by the enhancement of stress in tectonic regionsand the electromagnetic signal propagation from the earthquake preparation area. 2. Study of the seismo-ionospheric perturbation before the Tohoku-okiearthquake and Yushu earthquakeThe relationship between the behavior in the ionosphere and the2011Mw9.0Tohoku-Oki earthquake was analyzed using the GPS TEC data and ionosonde data. Itcan be found from the GIM TEC maps that during04-14UT on8March2011,3daysbefore the earthquake, there was an enhancement of TEC with an amplitude peak of40TECU appearing in the EIA region, southwest of the epicenter. In addition, thefoF2also recorded an unusual enhancement on8March by the four ionosondestations in Japan, of which the increase was larger in Okinawa and Yamagawa. Thetemporal-spatial distribution of the extreme TEC enhancement within30days beforethe earthquake was particularly pursued. It is found that the extreme enhancement waspersistently located in the region adjacent to the epicenter and the magnetic conjugatepoint for a long time of16h. It is noted that during the same period the solar activityalso had a large increase. The study indicates that only the solar radiationenhancement was not enough to produce the observed significant TEC enhancement.It means that the significant TEC enhancement on March8might be related to boththe M9.0Tohoku-Oki earthquake and the solar activity.Meanwhile, this thesis presents the ionospheric plasma variations before theYushu earthquake using both GPS and DEMETER data. The result from GPS showsthat TEC began to enhance20hours before the earthquake, appearing in the region15°N～30°N. The spatial characteristics of TEC perturbation were similar to thatbefore the Wenchuan earthquake. On the other hand, based on the DEMETERsatellite IAP and ISL data, this work studies the time series and spatial variations ofthe ionospheric plasma including Ne, Ni, O+, H+and He+before the earthquake, andfinds no disturbance correlated with the shock. It demonstrates that there are certaindifferences over the ionospheric disturbance with the elevation changes before theearthquake.3. Statistical analysis of electron density perturbation before major earthquakesobserved by DEMETER satellite and GPS measurementsBased on the data of DEMETER satellite, this work attempts to make a statisticalanalysis about the electron density perturbation before37major earthquakes ofmagnitude above7.0during January2005to December2009. The orbits, recorded in local nighttime by satellite, are chosen by a range of longitude20degrees and latitude15degrees during the9days around these earthquakes, with7days before and1dayafter. Among the37earthquakes, electron density perturbations were detected before19earthquakes, nearly accounting for51%. The anomalies were positive before18events and occurred mostly within1-6days before the shocks, part of which appearedmore than one time. Results indicate that it is more easily to observe the electrondensity disturbance around the equatorial and low-latitude regions than thehigh-latitude areas. The disturbance amplitude presents a positive correlation with themagnitude of earthquakes basically, while the depth of earthquakes does not showsignificant influence on the perturbation. It is worth noting that before several events,the anomalies are in the combined effect of earthquake and geomagnetic activity andpresent a higher disturbance level.This thesis studied the ionospheric anomalies associated with30earthquakesoccurred in China (including Taiwan) during2000to2010by examining theGPS-inferred TEC variations. It is shown that TEC perturbations were detected before20earthquakes among the30events, nearly67%of the total. The TEC anomaliesrepresent increase more often and occurred mostly within2-6days before the shocks,part of them appeared more than one time. And the pre-earthquake ionosphericanomalies appeared during12:00–20:00LT significantly. The analysis indicates thatthe anomalies were not so relevant to the magnitude of the forthcoming earthquakes.Both these upper and lower anomalies were also found in the magnetically conjugatedarea of the seismogenic zone to the geomagnetic equator. The spatial distributions ofthese anomalies are not of an east-west asymmetry and have an equatorward shift ofboth crests of the EIA.4. Long time series analysis of ionospheric TEC disturbance over seismicallyactive region in southwest China during low solar activityUsing data of Crustal Movement Observation Network of China (CMONC) thisthesis analyzes variations of TEC over southwest China during a period of low solarand geomagnetic activity in April-October2008. During that time, six largeearthquakes with magnitude M≧6.0occurred around the southwest region of China. To determine the abnormal TEC signals, a quartile-based processing is performed. Ateach time point we calculated the median M using the TEC values at the same localtime for the preceding15days. Known that the decisive role in the ionosphere state isperformed by space weather effects, we compared the TEC variations with time seriesof EUV solar radiation, Bz component of the interplanetary magnetic field (IMF),index of geomagnetic activity Dst and planetary index Kp, respectively. It is foundthat the observed anomalies in the regional TEC were in good correlation with thevariations of above solar and geomagnetic activities. We have not detected obviousTEC disturbance before five earthquakes expect for the Wenchuan earthquake. Inorder to additionally check the spatial occurrence of the observed anomalies, wechose a “check-region” with the same geomagnetic latitudes as the epicentral area ofthe six considered earthquakes, and analyzed the TEC changes. The results show thatthe time series of anomalous TEC in the “check-region” is similar to the epicentralarea, which is dominated by space weather. Therefore, it indicates the difficulties inidentifying earthquake precursors in the ionosphere TEC. The seismo-ionosphericcoupling process is complex, and it is necessary to strengthen the observation ofmulti-parameters on the ground, in the atmosphere and ionosphere synchronously.5. Preliminary study about modeling the pre-earthquake electrostatic effect onthe ionosphereThis thesis introduces the equations of the ionospheric currents and electricalconductivity tensor and summarizes the mathematical model and calculation methodsof the penetration of seisomogenic electrostatic field (SEF) into the ionosphere. Thecaused ionosphere effect by SEF was obtained by the O+continuity equation. It isshown that at night, the horizontally large scale SEF can efficiently penetrate into theionosphere and produce noticeable changes in the horizontal distribution of the Fregion electron density.