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Based on thresholding correlation techniques, the ionospheric TEC (Total Electron Content) anomalies are grouped into earthquake precursors if they met the criteria of a TEC anomaly that exceeds the threshold value and no geomagnetic storm events in the previus 0-2 days. Testing of the thresholding correlation techniques on ionospheric diurnal variations of GIM (Global Ionospheric Map) TEC data which were limited to cases of earthquakes above 8 Richter Scale, it gave test results of 60% successful of earthquake precursor detection. By using ame method, we have examined the thresholding correlation techniques for earthquake cases between Mw 7 - 8 magnitudes during 2016. The earthquakes' latitude were spread from high until mid-latitude and equatorial, so they gave very good analysis. The test results showed that there were 11 out of 16 cases or about 69% of ionospheric TEC anomalies can be classified as earthquake precursors, which could be seen 1 day up to few weeks before earthquakes. This percentage is slightly larger than the percentage of earthquake precursors over Mw 8 detected by the same technique which was only 63%. This is due to relatively fewer geomagnetic storms during the year 2016 compared to 2000 - 2012 periods that experiencing two peaks of maximum solar cycles. From two different periods of testing, it can be concluded that the thresholding correlation techniques have a greater chance for detecting earthquake precursors during low and minimum solar activity. [ABSTRACT FROM AUTHOR]

In this research, we observed Coseismic Ionospheric Disturbances (CID) of West Sumatra March 2nd, 2016 earthquake with GNSS-TEC. This earthquake had strike slip focal mechanism with earthquake moment magnitude 7.8 Mw. In order to observe ionospheric fluctuations, some GNSS stations owned by Geospatial Information Agency (BIG) were used, these stations were spread in Sumatera Island (CAIR, CBKT, CPAR, CPDG, and CSEL stations). The epoch of the GNSS Stations were 15 seconds which included GLONASS, GALILEO and GPS satellites. The CID analysis showed TEC anomalies at 11 to 15 minutes after the earthquake with magnitude 2 - 3.5 TECU. It was recorded by GPS satellites number 17 and GLONASS satellite number 14. The fluctuation of signal propagation velocity was about 0.98 km/s as acoustic wave which was calculated using peak to peak of the disturbance signal. Distance of CID signal could be observed around 600 km from epicenter with south-west location. Earthquake early warning system could not be observed in term preseismic ionospheric disturbances but appeared on seven days before the earthquake, which ionospheric anomalies was calculated using statistically method. Meanwhile, tsunami warning could be done using CID method if arrival time of tsunami is more than 15 minutes to coastline. [ABSTRACT FROM AUTHOR]

The occurrence of great earthquake as natural disaster is unavoidable and resulting a great loss in economy and human lives. So earthquake mitigation is a must to avoid greater loss in future. Past studies showed that there was ionospheric perturbation due to earthquake occurrence. This study analyzed the ionospheric Total Electron Content (TEC) before earthquake using Global Positioning System (GPS) data from Sumatran GPS Array (SuGAR) within 27 days using correlation technique. Correlation technique with anomaly threshold value was conducted to identify ionospheric variation related with earthquake preparation. From September 2007 until September 2012, 12 earthquakes occurred with magnitude > 6.0 over Sumatra, Indonesia. In result, ten of them preceded by TEC anomaly 1 to 24 days before earthquakes hit. The anomaly of TEC value is considered as effect of earthquake preparation activity after geomagnetic data validation. [ABSTRACT FROM AUTHOR]