Abstract
Several research proved that Earth's Magnetic Field anomaly can be caused by disturbance in the Earth. this phenomena has been observed as precursor of earthquake. The change of geomagnetic intensity might be affected by earthquake occurrences. Variation of geomagnetic data have been investigated in the occurrences of Lombok's Earthquake in 2018 with magnitude higher than 4.5 Mw. Geomagnet Sensor had been set up in North region of Lombok Island to derive geomagnetic data from September to October 2018. The Analysis was conducted by computing power spectrum density (PSD) of The Ultra Low Frequency (ULF) Signal of Z and H component. at the time, the Polarizations were noticed by comparing between Z and H component of PSD. The Result showed that the values of Z/H became higher a few days before the earthquake occurrence particularly on DOY 248 to DOY 256. Eventhough some distorsion signal were observed during that period, the overall data could be used as precursor of lombok earthquake in 2018.