Earthquakes are difficult to predict. An earthquake results from a sudden release of energy beneath the Earth's crust. Before earthquakes occur, the deformation of the Earth's crusts produces an electromagnetic radiation signal. Therefore, abnormal distributions of electric and magnetic fields can be observed in the deformation region. This electromagnetic radiation may influence the ionosphere. An ionosphere monitoring network that uses dualfrequency Global Positioning System (GPS) receivers is proposed here for earthquake detection. In general, an ionosonde is applied to measure the ionosphere. Its limitation is that ionosphere information can only be measured at a specific point rather than in an area. An alternative method of collecting ionospheric data is to use GPS receivers. The GPS signal travels from the satellite through the ionosphere to the ground. The refraction in the ionosphere can be used to estimate ionospheric parameters using GPS receivers. In addition, GPS reference stations are widely distributed around the world, which allows ionospheric parameters in a certain area to be easily calculated. The present study investigates the relationship between earthquakes and abnormal ionosphere variations using a network of dual-frequency GPS receivers. Two data filtering techniques are proposed to exclude undesired GPS data. The first data filtering technique concentrates on the causes of abnormal ionospheric phenomenon. Solar activity and earthquake-related radiation lead to anomalies in ionospheric variation. In order to exclude anomalous data caused by solar winds and storms, this paper applies the worldwide magnetic storm level, namely the Disturbance Storm Time (DST) index defined by the World Data Center of Geomagnetism (WDCG). A DST index of -50nT is used as the threshold. With the exclusion of irregular solar days, the unusual behaviors of the ionosphere can be assumed to be caused by local effects. The second data filtering technique is to verify the quality of the GPS signal by applying the code-carrier divergence algorithm to detect unreasonable steps in the pseudorange measurements. After these two filtering schemes, the remaining GPS observation data are ready to be evaluated for possible ionospheric anomalies due to earthquakes. This paper uses dual-frequency GPS pseudoranges to calculate the ionospheric delay. The calculated ionospheric delay is regarded as the basic parameter for ionosphere anomaly detection. GPS satellites appear in almost the same location every day. On selected normal days, each satellite's ionospheric delay will be aligned due to the period of the satellite not being exactly the same as that of the earth. The mean delay value of various satellites is regarded as the standard value. The threshold includes the data within two standard deviations of the mean. The ionospheric corrections for each satellite are evaluated with the standard ionospheric correction values. Areas with ionosphere anomalies are detected when the associated ionospheric correction is greater than the predefined threshold. This paper focuses on earthquakes with Richter scale magnitudes of over 7.0 due to their dramatic release of electromagnetic radiation. Two historical earthquakes, namely the 2006 Pingtung (Taiwan) earthquake and the 2004 Indian Ocean earthquake, with magnitudes of 7.1 and 9.1, respectively, are selected. GPS observation data from the seven days before the earthquakes occurred are used. The experiment results demonstrate that abnormalities in the ionosphere can be detected using the proposed method. These ionospheric anomalies may appear around the epicenter before the earthquake occurs. The relationship between the ionospheric anomalies and earthquakes is first examined, and then an earthquake detection scheme based on this relationship is developed.
|頁（從 - 到）||27-35|
|期刊||Proceedings of the Institute of Navigation Pacific Positioning, Navigation and Timing Meeting, Pacific PNT|
|出版狀態||Published - 2013|
|事件||Institute of Navigation Pacific Positioning, Navigation and Timing Meeting, PACIFIC PNT 2013 - Honolulu, United States|
持續時間: 2013 四月 22 → 2013 四月 25
All Science Journal Classification (ASJC) codes