Geomagnetic field data have been widely used by scientists to gain deeper insight of Earth’s interior's activities and the surrounding space environment. We have been utilizing ground-based magnetometer data provided by Magnetic Data Acquisition System (MAGDAS) of Kyushu University in exploring earthquake and solar flare phenomena.

  Earthquake forecasting by observing anomalous geomagnetic emission were mostly accomplished by utilizing either one of these signal processing methods: polarization ratio analysis (PRA) and diurnal variation ratio (DVR). In order to objectively compare their performances, the M6.9 Visayas, Philipines earthquake on 6th February 2012 was selected as a case study. Geomagnetic field data from two MAGDAS stations located in close proximity to the epicentre (i.e. Cebu and Legazpi stations) were acquired and processed. A precursory anomaly was found using the PRA method, which appeared 2 weeks before the earthquake. In contrast, the DVR method did not reveal any prominent anomaly to be considered as precursor. The difference between the performances of the two methods may be attributed to the studied earthquake having a low magnitude, which possibly emitted weaker geomagnetic emission during the pre-earthquake phase. Nevertheless, the PRA method was shown to be effective in detecting possible precursor of upcoming earthquake, thus have bigger potential to be utilized in real-time prediction.