Analysis of Preseismic Event Using Seismo-electromagnetics Data

The megathrust region of Sumatra is an active seismic area. Before the earthquake happened, geomagnetic field anomaly was recorded at the geomagnetic recording station located in Sumatera. In the lithospheric layers that gain stress and strain before an earthquake generate electromagnetic emissions that can be recorded at a geomagnetic station at a certain distance. The electromagnetic emission propagation passed the rock until it reaches the ionosphere which is often called the LAI coupling (Lithosphere, Atmospheric, and Ionosphere). The purpose of this study is to confirm the existence of geomagnetic field anomalies before the earthquake. This research uses the earthquake data in Sumatera region with period between August to October 2016. The earthquake data used were Mukomuko earthquake August 24 (M 5.8), South Bengkulu earthquake September 17 (M 5.4), and Padang earthquake October 21 (M 4.5). The geomagnetic sensor used is MAGDAS 9 located at 3 stations in Gunungsitoli station, Sicincin station, and Liwa station. The method used is the ULF data signal filtering method from the multi-station geomagnetic data to obtain an azimuth geomagnetic field anomaly. From the research results obtained lead time ranged between 9 to 18 days before the earthquake. The results from the azimuth direction of the geomagnetic field anomaly correlated to the epicenter location of the earthquake.