摘要：AbstractAnomalous Ultra Low Frequency signals observed by ground-based magnetometers that linked with seismic events are commonly accepted. These anomalous signals can be promising phenomena for constructing early Earthquake-warning systems. The present study analyzes high-resolution (1-s) geomagnetic data recorded at the Kototabang (KTB) station, Indonesia, and other remote reference stations to detect the occurrence of any anomalous ULF signals that may associated with a number of seismic events occurred in Sumatra, Indonesia. The amplitude of the ULF emissions in the Pc3 range (10–45 s) was examined during three big seismic events that occurred in Sumatra between 2004 and 2007. Results of data processing and analysis indicate the presence of anomalous enhancement in the Pc3 amplitude ratio (ZPc3/HPc3) at KTB station in association with the studied seismic events. On the other hand, there are no noticeable changes at other distant reference stations during the examined periods. In addition, there are no remarkable external geomagnetic disturbances during the studied seismic events as it reveals from the Disturbance storm time (Dst) index. So, we can conclude that the observed anomalous changes might be a possible signature related to the above-mentioned seismic events in Sumatra, Indonesia.
