Analisis Big Data Geomagnetik Dengan Metode Diferensiasi Sebagai Prekursor Gempa Lombok Tahun 2018

Lombok is an area with the highest geomagnetic anomaly in Indonesia (Zubaidah et al., 2014). From the end of July to the end of August 2018, Lombok experienced a series of fairly large earthquakes. Identification of geomagnetic signals, especially in the Ultra Low Frequency (ULF) spectrum, can be used as earthquake precursors (Saroso, 2010). Intermagnet IAGA (International Aeronomy Geomagnetic Association) is a network of international geomagnetic observatory stations that have large world geomagnetic data. Big data analysis is very important because very large information is needed in disaster mitigation. This study uses geomagnetic data per second for 24 hours from 28 August to 30 November 2018 taken from Kakadu (KDU) Australia and Nurul Bayan Station (NRB) Lombok. The analytical method used is Differentiation by calculating the F value (total magnetic field) for KDU and NRB, then look for the difference and analyze the pattern. The results found that there was an anomaly phenomenon of the Earth's magnetic field in Nurul Bayan Lombok which was detected for 17 days during October 2018.

Equatorial auroral records reveal dynamics of the paleo-West Pacific geomagnetic anomaly

Localized regions of low geomagnetic intensity such as the South Atlantic Anomaly allow energetic particles from the Van Allen radiation belt to precipitate into the atmosphere and have been linked to a signature in the form of red aurora–like airglow visible to the naked eye. Smoothed global geomagnetic models predict a low-intensity West Pacific Anomaly (WPA) during the sixteenth to nineteenth centuries characterized by a simple time dependence. Here, we link the WPA to an independent database of equatorial aurorae recorded in Seoul, South Korea. These records show a complex fluctuating behavior in auroral frequency, whose overall trend from 1500 to 1800 AD is consistent with the locally weak geomagnetic field of the WPA, with a minimum at 1650 AD. We propose that the fluctuations in auroral frequency are caused by corresponding and hitherto unknown fluctuations in the regional magnetic intensity with peaks at 1590 and 1720 AD, a time dependence that has been masked by the smoothing inherent in regularized global geomagnetic models. A physical core flow model demonstrates that such behavior requires localized time-dependent upwelling flows in the Earth’s core, possibly driven by regional lower-mantle anomalies.

Geomagnetic anomaly associated with Fukushima earthquake on February 13th, 2021

In this study, we performed research on electromagnetic anomalies related to earthquakes as early signs (precursors) that occurred in Fukushima, Japan on February 13th, 2021. The research focused on the utilization of geomagnetic field data which was derived from the Kakioka (KAK), Kanoya (KNY), and Memambetsu (MMB) observatories, particularly in the ultra-low frequency (ULF) to detect earthquake precursors. The method of electromagnetic data processing was conducted by applying a polarization ratio. In addition, we improved the methodology by splitting the ULF data (which ranged from 0.01-0.1 Hz) into 9 central frequencies and picking up the highest value from each central frequency to get the polarization ratio. The anomaly of magnetic polarization was identified 2-3 weeks before the mainshock in a narrowband frequency in the range of 0.04-0.05 Hz.

Modeling of Complex Geological Body and Computation of Geomagnetic Anomaly

Modeling plays an important role in engineering exploration. However, the traditional rectangular mesh cannot meet the requirement because the actual shape of the model may be very complex. Therefore, this paper chooses the Delaunay grid for modeling and applies this method to magnetic numerical simulation. At the same time, we make use of the advantages of the Delaunay grid and choose to use grid encryption technology in the boundary and complex area of the model. Then, the formula for calculating the magnetic anomaly of tetrahedron is deduced in detail, and the magnetic anomaly with surface fluctuation is calculated. For a synthetic data model, Delaunay grids with different densities are used to model and calculate surface anomalies. The two results are compared with the analytical solution of the model. The results show that the method has high accuracy. Then, the method is applied to the actual geological body modeling in the Jinchuan mining area. According to local needs, a three-dimensional model with inhomogeneous grid density is established and the surface magnetic field of the model is calculated. Finally, the simulation data are compared with the measured data. The results show that the Delaunay grid modeling method has strong applicability.

ANALISIS ANOMALI SINYAL ULTRA LOW FREQUENCY BERDASARKAN DATA PENGUKURAN GEOMAGNETIK SEBAGAI INDIKATOR PREKURSOR GEMPABUMI WILAYAH LAMPUNG TAHUN 2016

Regional research had been done to analysis anomalies signal of ultra low frequency based on measurement data as an indicator of the geomagnetic earthquake precursor of lampung in 2016. To achieve purpose of the study conducted by the following steps: (i) Calculation of the total magnetic field of data; (ii) Daily Trend Analysis; (iii) the Fourier transform of the data Geomagnetic Anomaly; (iv) Localization Frequency ULF; (v) Calculation of Ratio Vertical-Horizontal (Polarization Ratio Z / H); (vi) Correction magnetic storms or Disturbance Strom Time (DST); (vii) the identification of earthquake precursors; (viii) Determination of OnsetTime, leadtime,and the direction of precursors. The results of the analysis of ten earthquakes with a magnitude above 5 MW have precursors between 11 to 30 days before an earthquake. Nine out of ten earthquakes studied had an earthquake precursors and precursors that do not have, this is because the distance is too far from the station Magdas in Liwa, West Lampung. Thus it can be seen that the precursor using the magnetic data can be used to make short-term predictions.

Estimating Primary Tin Deposits Using Resistivity Method and Geomagnetic Method in Sambunggiri Hill Merawang District, Bangka Regency)

Cassitterit is a valuable mineral containing tin and other minerals as mining products in the Bangka Belitung Islands region. Sambung giri Hill, Merawang District, Bangka Regency is one of the places where primary tin deposits occur. Estimation of subsurface images can be interpreted using geophysical methods in the form of resistivity methods and geomagnetic methods. The measurement of resistivity method uses 6 lines with dipole-dipole configuration while the geomagnetic method with looping measurement technique as many as 13 lines with each line consists of several measurement points within 20 meters, consisting of 10 lines to the South-North direction, and 3 trajectories to the West- East. Based on the results of the study, the primary tin deposit estimation from the resistivity method in the form of a cross section of resistivity shows a low resistivity value (<700 Ohm.m) while the geomagentic method in the form of Reduction To Equator (RTE) shows a low geomagnetic anomaly (<0.8 nT). The spread of primary tin deposits is estimated to be found in the Northwest-Southeast direction.