Correlation of geomagnetic signal for earthquake studies in Indonesian, Australian and Pacific regions

In order to obtain earthquakes precursors in Indonesian regions, some researchers have used data from Indonesian geomagnetic observatories and surroundings. Comparisons of geomagnetic signals are often used to get anomalous signals that can be associated with earthquake occurrences. However, deep study has not been provided to convince that the data of each observatory has a strong correlation. Even though that if and only if strong correlations found on normal days (i.e. days without earthquakes), it can confirm that the earthquake precursors are valid. This paper examines geomagnetic data recorded on Indonesian observatories in Lombok (LOK), Kupang (KPG) and Pelabuhan Ratu (PLR), on Australian one in Kakadu (KDU) and on Pacific one in Guam (GUA). Spearman Rho correlation method is used to determine the strength of relationships between geomagnetic data. One-minute data on several days in the year of 2012, 2014, and 2015 were used as sample for data processing. Results show that strengths of relationships of strong to very strong are found in KPG-PLR, KPG-KDU, KPG-GUA, PLR-GUA, and LOK-KPG; while in LOK-KDU and LOK-GUA the relationships are quite strong to very strong. Low strong to very strong are found in PLR-KDU and KDU-GUA. All observatories show positive directions of relations, means that increase in amplitude of data in one observatory will be followed by the same amount of increase in other observatories. Future studies are still needed to examine in detail the correlations, with special attention to the influence of daily (between day and night) and seasonal (between winter/wet and summer/dry) variations.