<![CDATA[Sinyal radio frekuensi-ganda yang dipancarkan dari satelit Global Positioning System (GPS) memungkinkan untuk pengukuran jumlah total elektron, disebut sebagai total electron content (TEC), di lapisan ionosfer sepanjang berkas sinyal antara satelit dan penerima GPS. Pengolahan diferensial TEC (dTEC) secara spasial dan slant TEC menggunakan data jaringan Sumatran GPS Array (SUGAR) dengan memakai perangkat lunak algoritma GAMIT (GPS Analysis at Massachusetts Institute Technology). Sedangkan variasi dan distribusi vertical TEC diolah dengan perangkat lunak matlab7. Hasil analisis menunjukkan adanya variasi nilai TEC baik itu penurunan maupun peningkatan jumlah elektron. Selama kurun waktu bulan Desember 2004 sampai April 2005 di Sumatera terjadi 10 kali gempabumi dengan kekuatatan M ≥ 6.0 dimana 9 gempabumi diantaranya muncul anomali TEC (penurunan nilai TEC dibawah nilai batas bawah) 1 sampai 6 hari sebelum gempabumi terjadi. Anomali TEC ini dapat dipandang sebagai pertanda (precursory signal) yang muncul sebelum terjadi gempabumi. The double-frequency radio signal which is broadcasted by Global Positioning System (GPS) Satellite enables to measure the number of Total Electron Content (TEC). It exists along ionosphere between the signal beam and GPS receiver. The calculation of TEC differential ( dTEC ) and slant TEC use the Sumatra GPS Array ( SUGAR ) network data. It is done by utilizing the GAMIT (GPS Analysis at Massachusetts Institute of Technology) algorithm software. The distribution of variation and vertical TEC are processed by using Matlab 7 Software. The result of the analysis shows the existence of TEC value both the decrease and the increase of electrons number. From December 2004 until April 2005, ten earthquakes occurred in Sumatra with the magnitude M>6.0. Nine of them appeared the TEC anomaly (the decrease of TEC value is below the lower bound) in 1 up to 6 days before the earthquakes stroke. The TEC anomaly is considered as the precursory signal that occurs before the earthquake strikes.]]>
