Seismic-ionospheric effects prior to four earthquakes in Indonesia detected by the China Seismo-Electromagnetic Satellite

Based on the promising the seismic-ionospheric research, the China government launched the Seismo-electromagnetic satellite (CSES) on February 2018, for both the earthquake observation and geophysical field research. As the data is available, we adopt the observed data from CSES satellite in our research.

There are four consecutive shallow-focus EQs in a short period in Lombok, Indonesia during July to August 2018. First, we calculate the percent disturbance of electron density (Ne) on each orbit from CSES satellite. It is found that there are mainly four significant abnormal enhancements at orbits 26600 on July 27, 27210 and 27281 on July 31, 28270 and 27351 on August 7, 29340 on August 14, respectively. Compared with the earthquake time, these four disturbances just happened before the four earthquakes, which maybe the seismic-ionospheric effect. After checking different kinds of space weather index, we can exclude that the disturbance is caused by geomagnetic or solar activities.

As for the IRI model is the background data without any seismic factors, we adopt the corresponding Ne data from IRI-2016 to evaluate the reliability of CSES data. The abnormal orbits also show the similar disturbance. Then the CODE TEC was adopted to calculate the global VTEC disturbance. There are significant anomalies in the north of epicenters which lasted for almost 9 hours not changing over time, and the disturbed zones are within 90º-130ºE in zonal direction, 0º-15ºN in the meridional direction. These results are mainly consistent with Ne observed by CSES.

In the following research, we counted all the earthquakes occurred in Indonesia over a 10-year period during 2007-2017 between 106.45°E-126.45°E and 8.3°S-1.7°N to check the anomalies of CODE TEC. After selecting the earthquake accidents with depth less than 50 km, and magnitude larger than M5.8, there are a total of 35 qualified seismic activities. By counting the TEC anomalies 15 days before and after these 35 earthquakes, which indicates obvious anomalies 1-7 days before one earthquake in Indonesia, the number of ionospheric parameter anomalies is more than other time. It is highly suggestive that the positive anomalies of Ne and TEC are the seismic-ionospheric effects preceding the earthquakes in Indonesia