Xuhui Shen

Ionospheric perturbations of electron density before the Wenchuan Earthquake

Based on electron density data recorded by the Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions (DEMETER) satellite of France, the phenomena of disturbed electron density in the ionosphere before the Wenchuan Earthquake of magnitude 8.0 on 12 May 2008, were analysed. The results showed that the anomalies concentrated 3 days prior to the earthquake, especially the variation on 9 May, when the electron density reduced above the northeast epicentral area, and the peak values moved to the equator. Compared with the variations in the geomagnetic indexes and other parameters related to solar activity, the geomagnetic condition and solar activity were all quiet from 7 to 12 May, so the variation on 9 May might be related to this strong earthquake. In addition, the geomagnetic field observed at the surface was analysed, and the Z component data at stations near the epicentral area showed apparent aberrations of daily variation compared with those at stations in eastern China. All these phenomena illustrate that obvious perturbations in the ionosphere and at the surface might be related to the preparation process of the Wenchuan Earthquake.

A new method to study the time correlation between Van Allen Belt electrons and earthquakes

ABSTRACT A new method to study a possible temporal correlation between hundreds of keV Van Allen Belt electrons and strong earthquakes is proposed. It consists in measuring the electrons pitch angle distribution (PAD), searching for PAD disturbances, and studying the time correlation between these PAD disturbances and strong earthquakes, occurring within a defined time window. The method was applied to measurements of energetic electrons, which were performed with the Energetic Particle, Composition, and Thermal Plasma (ECT)-MagEIS detector on board the Van Allen Probes (VAPs) mission and strong continental earthquakes, with magnitude M 5.0 and hypocenter depth 100 km. We report the correlation studies for electrons with energies of about 350 keV, with which a 3.84 standard deviations correlation peak was found at hour time bin, and about 450 keV with which no correlation peaks above 2.0 standard deviations were found. Our work proves the feasibility of the proposed method and the obtained results add useful and additional information with respect to past studies.

Variations of ionospheric plasma at different altitudes before the 2005 Sumatra Indonesia Ms 7.2 earthquake

Resent years, many researchers pay more attention to abnormities before earthquake, and in this study, seismo-ionospheric synchronous disturbances at different altitudes by GPS and satellite observations were firstly studied around one Sumatra Indonesia Ms 7.2 earthquake occurred on July 5 2005. By using the same temporal and spatial methods, data of GPS-TEC from JPL, electron density (Ne) from DEMETER and ion density (Ni) from DMSP were deeply analyzed. The ionospheric plasma disturbances in GPS-TEC and increasement of Ne at 710 km were found on July 4, and plasma density at the three altitudes has all increased on July 7 after the earthquake. All the disturbances were not just above the epicenter. TEC perturbations have happened at the east of the epicenter for the two days, and electron density enhancement at 710 km has moved to west of the TEC perturbations at the same time on July 4, which may be caused by E × B drift. The moving direction of up-going plasma was simulated using SAMI2 model. The results have shown that the plasma will move to higher altitude along the geomagnetic force line, which could exactly account for the plasma density enhancement in the northern direction of the geomagnetic south latitude earthquake.

Wavelet-Based method for detecting seismic anomalies in DEMETER satellite data

In this paper we present an analysis of DEMETER (Detection of Electromagnetic Emissions Transmitted from Earthquake Regions) satellite data by using the wavelet-based data mining techniques. The analyzed results reveal that the possible anomalous variations exist around the earthquakes. The methods studied in this work include wavelet transformations and spatial/temporal continuity analysis of wavelet maxima. These methods have been used to analyze the singularities of seismic precursors in DEMETER satellite data, which are associated with the two earthquakes of Wenchuan and Pure recently occurred in China.

Extracting seismic anomalies based on STD threshold method using outgoing Longwave Radiation data

In this paper, STD (standard deviation) threshold method was proposed using to detect OLR (Outgoing Longwave Radiation) seismic anomalies. OLR data describe the radiation information from the top of the atmosphere, which be thought to reflect the energy changes of earth-atmosphere system prior to earthquakes. The method to identifying seismic anomaly and non-seismic anomaly has been proposed in this work. Based on this, Wenchuan Sichuan, May 12, 2008, Ms8.0 and Delingha, Qinghai, November 10, 2008, Ms6.3 have been studied respectively using STD threshold method. The results indicate that the seismic infrared radiation anomalies can be detected using STD threshold method. And these anomalies can reflect the process of earthquake preparation. At the same time, the spatial distributions of OLR anomalies have some indication effect on judge the seismogenic structure and the epicenter.

Automatic collecting technique of low frequency electromagnetic signals and its application in earthquake study

Two methods to automatically collect disturbed ultra low frequency electromagnetic signals before strong earthquakes were developed in this paper, in which one is only related to the spectrum intensity of electric field, and another is additionally combined with fractal dimension feature in electromagnetic emissions. Both techniques were applied for satellite data processing, case study and precursor distinction around Chile earthquakes, especially those occurring in 2010. Their advantages and disadvantages were compared and discussed based on actual application results. Further research on data mining needs to be carried out to improve the old and to develop the new ones based on the property of electromagnetic waves and multi parameters.

Study on the electronic density perturbation detected by DEMETER satellite before Wenchuan earthquake

We used slope analysis and sliding Median method to study the electron density data observed by Langmuir probe of DEMETER satellite since April 25, 2008 to May 11, 2008, and obvious perturbation phenomena of electron density(Ne) in ionosphere were found before Wenchuan earthquake on May 12, 2008. Considering the geomagnetic disturbances, there were some abnormal information in different degrees on May 3, 4, 7, 9, 10, 11 respectively. Furthermore, on May 3 and May 4, along with the change of electron density, electron temperature was also elevated at the latitude of 10∼30°N. Also on May 7, not only electron density increased, but also ion density did above the epicentral area.

Application of outgoing longwave radiation data for earthquake research

Satellite thermal infrared (TIR) data have revealed anomalies prior to major earthquakes. The paper presents the potential relationship between outgoing longwave radiation (OLR) anomalies and earthquakes. The method used in this work is to subtract long-lived background from initial data and have been applied to detect seismic anomalies successfully, particularly to a comparative study of the two earthquakes of Yunnan earthquake and Myanmar-China border region earthquake in June, 2007.

Three-dimensional deformation field caused by the Gaize earthquake by Multi-LOS DInSAR measurement technology

This paper firstly presents the Multi-LOS DInSAR measurement result of the coseismic deformation field caused by the Gaize Ms6.9 mainshock and Ms6.0 aftershock in Tibet, China, and then obtain the 3D deformation field based on the 3D resolving mode. The characteristic analysis of coseismic deformation field shows the rupture of mainshock is majorly normal, left-lateral striking with a little rotation; and the aftershock is typical normal rupture nature. The mainshock and aftershock had induced the east and west rupture(maybe buried) successively, and produced the east and west two subsiding centers

Ionospheric disturbances associated with Tonga Mw7.9 earthquake —Results from Langmuir Probe Instrument onboard DEMETER satellite

Authors in this paper mainly employ Ne (electron density), and Te (electron temperature) data of Langmuir Probe Instrument (ISL) onboard DEMETER, to study the variations of electron density and electron temperature associated with strong earthquakes. Tonga Mw 7.9 earthquake case study shows that revisited orbits of 09768_1 and 09782_1 (before and after shock, respectively) within 4 months data before earthquake and 2 months data after earthquake changed significantly before earthquake. Te data recorded by 09768_1 and its revisited orbits before earthquake were lower about 1000K to 1500K than recorded after earthquake, whereas Ne data of the same orbits not occurred such distinctive changes. Ne data of 09782_1 and its revisited orbits experienced an increase from 20000cm−3 to 30000cm−3. To further understand the features of the pre-earthquake ionospheric anomalies, we examine the temporal and spatial evolution of electron density within the area of 2000km near epicenter from 1st March to 1st July 2006 and from 1st March to 1st July from 29st April 2005 to 2nd May 2005 respectively. Results show that about the 5 days ago before earthquake the electron density dropped to a relative lower level comparing to the normal days without earthquakes.