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"Pulau Jawa berada di dekat zona subduksi Lempeng Eurasia dan Indo-Australia, yang menyebabkan terbentuknya patahan-patahan di daratan. Salah satu daerah yang terdampak adalah Kabupaten Sumedang, Jawa Barat. Prediksi gempabumi penting untuk meminimalisir kerusakan. Analisis aktivitas anomali geomagnetik Ultra-low Frequency (ULF) sebelum gempabumi dilakukan di sekitar stasiun geomagnetik TJS Sumedang menggunakan metode Polarization Ratio Analysis (PRA). Metode ini membandingkan nilai medan magnetik komponen vertikal terhadap horizontal (SZ/SG) berbasis Fast Fourier Transform (FFT) untuk mendeteksi anomali geomagnetik ULF (0.01 Hz - 0.04 Hz). Frekuensi ini dipilih karena mudah merambat ke permukaan, memungkinkan deteksi anomali yang jelas. Tiga gempabumi tahun 2020-2021 dengan magnitudo (M) ≥ 5 dan jarak episenter (R) ≤ 150 km (10 Maret 2020, M5; 25 Oktober 2020, M5.4; dan 27 April 2021, M5) dianalisis. Data geomagnetik malam hari komponen X, Y, dan Z dipilih untuk mengurangi noise. Hasil menunjukkan frekuensi 0.01 Hz - 0.04 Hz optimal mendeteksi prekursor gempa pada 27 April 2021. Anomali geomagnetik ULF tidak berkaitan dengan badai geomagnetik, dibuktikan dengan nilai indeks Dst (Disturbance storm time) yang tidak melebihi ambang batas.

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Java Island is adjacent to the subduction zone of the Eurasian and Indo-Australian Plates, causing the formation of several faults on land. From the formation of faults that can be caused by earthquakes, there are areas that are affected, one of which is Sumedang Regency, West Java. Earthquake prediction efforts are very important to minimize the damage that will occur. Ultra-low Frequency (ULF) geomagnetic anomaly activity was analyzed before the earthquake around the TJS Sumedang geomagnetic station using the Polarization Ratio Analysis (PRA) method, which compares the magnetic field value of the vertical component to the horizontal component (SZ/SG) based on Fast Fourier Transform (FFT), which is used to convert data from the time domain into the frequency domain to see ULF scale geomagnetic anomaly activity from 0.01 Hz - 0.04 Hz because this frequency wave easily propagates to the surface, allowing clear anomaly detection. Three earthquakes in 2020-2021 taken at magnitude (M) ≥ 5 and earthquake epicenter (R) ≤ 150 km (EQ1 with M5 on March 10, 2020, EQ2 with M5.4 on October 25, 2020, and EQ3 with M5 on April 27, 2021) in the vicinity of the TJS Sumedang geomagnetic station were selected because the larger the M and the closer the R of the earthquake can strengthen the geomagnetic anomaly readings. Nighttime geomagnetic data of X, Y, and Z components were selected to reduce noise or human activity. The results showed that the frequency of 0.01 Hz - 0.04 Hz was optimal for detecting possible precursors of the M5 earthquake on April 27, 2021 (EQ1), and the ULF geomagnetic anomaly in this study was not related to geomagnetic storms, which was obtained from the Dst (Disturbance storm time) index value which did not exceed the threshold line."

"Pengolahan data magnetik menghasilkan nilai magentik total yang telah dikoreksi oleh koreksi IGRF, Variasi Harian dan Koreksi Drift. Hasil pengolahan data kemudian diplot menjadi kontur anomali magnetik pada software SURFER 9.0. Dari kontur inilah kemudian didapatkan indikasi anomali magnetik pada data pengukuran. Anomali inilah yang nantinya akan dijadikan patokan untuk membuat permodelan. Permodelan menggunakan data magnetik bertujuan untuk mengidentifikasikan anomali magnetik yang terdapat pada data pengukuran. Anomali magnetik biasanya dipengaruhi oleh hot rock yang berada pada bawah permukaan. Pada penelitian ini, data magnetik yang digunakan adalah data pengukuran magnetik di daerah Arjuna-Welirang. Daerah prospek geothermal Arjuna-Welirang terletak di wilayah Kabupaten Malang, Kabupaten Mojokerto, Pasuruan, dan Kota Batu. Daerah prospek ini berada di lingkungan geologi yang didominasi oleh batuan vulkanik berumur kuarter.

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Magnetic data processing give a magnetic total value that has been corrected by the correction IGRF, Diurnal Variety and Drift Correction. Then the data processing?s results are plotted into the contours of the magnetic anomalies in the software Surfer 9.0. This contour is then obtained an indication of magnetic anomalies on the measurement data. This is an anomaly that will be used as a benchmark for modeling. Modeling using magnetic data aims to identify magnetic anomalies are present in the measurement data. Magnetic anomalies are usually influenced by the hot rock that is on the bottom surface. In this study, which used magnetic data is the data of magnetic measurements in the Arjuna-Welirang. Geothermal prospect area Arjuna-Welirang located in Malang regency, regency Mojokerto, Pasuruan, and Batu. This prospect area is located in the geological environment which is dominated by old volcanic rocks quarter."

"Geomagnetic storm represents natural phenomenon caused by interaction between high speed solar wind and magnetosphere which is associated with southward interplanetary magnetic field. By processing data of H geomagnetic storm, it is obtained that amplitude and depression of H geomagnetic component intensity distribution show similar pattern, close to exponential model."

"A magnetic Fe3O4@ZnO nanocomposite (NC) was successfully synthesized by a wet milling method using a high energy milling (HEM) machine. The magnetic Fe3O4@ZnO NC was characterized by an X-ray Diffractometer (XRD), scanning and transmission electron microscopes (SEM and TEM), and a vibrating sample magnetometer (VSM). X-ray diffraction results show that Fe3O4@ZnO NC consisted of ZnO and Fe3O4 phases. The microstructure analysis indicated that Fe3O4@ZnO NC presented a ZnO shell wrapped around the surface of a magnetic Fe3O4 surface. The average diameter of the aggregated Fe3O4 nanoparticle (NP) is 20 nm, while that of Fe3O4@ZnO NCs is nearly 30 nm. The Fe3O4 NP and Fe3O4@ZnO NC show typical superparamagnetic behavior with low coercivity. The saturation magnetization (Ms) of Fe3O4 NP was measured at about 66.26emu.g-1 and then declined to 34.79emu.g-1 after being encapsulated with a ZnO shell. The photoactivities of the Fe3O4@ZnO NC under UV irradiation were quantified by the degradation of a methylene blue (MB) dye solution. The result reveals that the photodegradation efficiency of Fe3O4@ZnO NC is favorable at pH neutral (pH = 7) reaching 100%. By increasing the MB dye concentration from 10 ppm to 40 ppm, the photodegradation efficiency decreases from 100% to 52%. The Fe3O4@ZnO NC can be easily collected by an external magnet. The magnetic Fe3O4@ZnO NC could be extended to various potential applications, such as purification processes, catalysis, separation, and photodegradation."

"Pengujian tingkat ketelitian metode reduksi anomali medan magnetik total bumi ke kutub utara menggunakan sumber ekivalen dipol berbasis model komputasi telaah prisma tegak. Ketidakrataan permukaan topografi, variasi dimensi sumber anomali (distrubusi magnetisasi) dan ketidakteraturan distribusi titik pengukuran tidak berpengaruh secara signifikan terhadap ketelitian metode. Tingkat ketelitian metode sangat tergantung pada kedalaman lapisan sumber ekivalen dipol. Batas atas dan bawah kedalaman lapisan sumber ekivalen dipol tergantung pada spasi pengukuran. Batas atas kedalaman lapisan sumber ekivalen dipol dengan penyimpanan rata-rata di bawah 10 % berkisar 3 kai spasi pengukuran sedang batas bawah kedalaman lapisan sumber ekivalen dipol tergantung pada dimensi sumber anomali "

"Anomali Bouger lengkap merupakan superposisi dari anomali regional dan anomali residual. Anomali regional berasosiasi dengan kondisi geologi umum yang dominan pada daerah penelitian. Hal ini biasanya dicirikan oleh anomali yang berfrekuensi rendah. Sebaliknya, anomali residual umumnya memiliki frekuensi tinggi dan memiliki informasi mengenai sumber anomali dangkal. Studi ini mengaplikasikan filter frekuensi pada data anomali Bouger sintetik. Penggunaan metode filter frekuensi pada harga tertentu diharapkan dapat menghasilkan anomali regional dan residual yang tepat. Studi ini memiliki tujuan untuk mengkorelasikan hubungan antara variasi grid spasi dengan kedalaman benda anomali serta korelasi antara kedalaman anomali dengan besar lebar jendela N. Penggunaan grid spasi yang sembarang kemungkinan akan menyebabkan benda yang menjadi target pengukuran tidak tercapai. Penulis mengasumsikan penggunaan grid spasi yang tepat dalam proses survei geoteknik maupun geofisika sangat penting. Untuk menguji metoda serta asumsi penulis tersebut, dibuat tiga model sintetik yaitu model geoteknik (50 m), model eksplorasi mineral (500 m), dan model sistem geothermal (6000 m). Pemisahan anomali regional – residual menggunakan lowpass filter frequency menghasilkan anomali regional yang sesuai dengan anomali akibat benda dalam.

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Complete bouger anomaly is the superposition of regional anomaly and residual anomaly. Regional anomaly is associated with general geological condition that dominat at reasearch area. This is characterized by low frequency anomaly. The opposite, residual anomally generally has high frequency and has informations about the source of residual anomaly. This study applies filter frequency on synthetic bouger anomaly data. The application of filter frequency on certain value is expected to give approximate regional and residual anomaly as the result. The objectives of this study is also to connect variation. The objectives of this study is also to relate the variation in grid spacing and the depth of anomaly object and also to state the relation between the depth of anomaly and the value of the width of window N. Use of an arbitrary grid spacing will likely cause the target measurement object are not reached. The author assumes the proper use of grid spacing in the geotechnic and geophysics surveys is essential. To test the method and the writer’s assumption, 3 synthetics models were made, geothectonic (50 m), mineral exploration model (500 m) and also geothermal system model (6000 m). Separation between residual and regional anomaly using frequency filter (low pass filter frequency) produces regional anomaly fits to subsurface body."

"Series of Ti2+-Mn4+ ions substituted BaFe12-2xTixMnxO19 samples with x = 0.0–0.8 have been studied to find out the effect of ion substitution on their microstructure, magnetic, and microwave absorption characteristics. The materials were synthesized through the mechanical alloying process. X-ray diffraction pattern for all sintered samples confirmed that the materials are single phase materials with BaFe12O19 structure. Referring to the results, it is shown that all samples that are subject to ultrasonic irradiation treatment characterized by a crystallite size distribution with the width get slimmer and mean crystallite size get smaller as the substitution level increased from x = 0 to x = 0.8. A sample of latter composition has fine crystals between 10–200 nm with the mean size of 42 nm. The effect of ionic substitution also affected the magnetic properties in which coercivity decreased proportionally with an increase of x value. The saturation magnetization increased to 0.41 T at x = 0.4, and then decreased for higher x values. Hence, the increase occurred only in samples with low-level substitutions of Ti2+-Mn4+ ions. Microwave absorption characterization clearly shows that the reflection loss (RL) value of Ti2+-Mn4+ substituted BaFe12-2xTixMnxO19 samples was enhanced from 2.5 dB in a doped free sample (x = 0) to 22 dB (~92% absorption) in a sample with x = 0.6 in the frequency range 8–12 GHz."

"Dalam melakukan interpretasi struktur bawah permukaan menggunakan data gravitasi, perlu dilakukan pemisahan anomali residual dan regional. Metode yang umum digunakan untuk melakukan pemisahan antara lain yaitu metode analisis spektrum, trend surface analysis (TSA), dan upward continuation. Dalam tulisan ini digunakan ketiga metode tersebut untuk memisahkan anomali regional dan residual. Penelitian dilakukan menggunakan data gravitasi daerah “X” dengan objek penelitian berupa patahan. Data gravitasi yang diperoleh diolah hingga mendapatkan data CBA (Complete Bouguer Anomaly), lalu dilakukan proses separasi. Dari data-data tersebut kemudian dilakukan inversi dan forward modeling 2D. Analisis dilakukan untuk melihat perbedaan hasil pemodelan anomali gravitasi tanpa dilakukan separasi (CBA) dibandingkan dengan pemodelan anomali residual hasil separasi. Hasil analisisnya memperlihatkan bahwa dari data CBA dan anomali residual metode analisis spektrum tidak dapat mendeteksi adanya patahan. Sedangkan dari data anomali residual metode TSA dan upward continuation sudah mampu mendeteksi adanya patahan.

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In interpreting subsurface structures using gravity data, it is necessary to separate residual and regional anomalies. The methods commonly used to perform separation include spectrum analysis, trend surface analysis (TSA), and upward continuation. In this paper, these three methods are used to separate regional and residual anomalies. The study was conducted using gravity data for area “X” focusing on fault structures as the object of interest. The obtained gravity data is processed to obtain CBA (Complete Bouguer Anomaly) data, then the separation process is carried out. From these data, 2D inversion and forward modeling are then performed. The analysis was carried out to see the differences in the results of the modeling of the gravity anomaly without separation (CBA) compared to the modeling of the residual anomaly resulting from the separation. The results of the analysis show that from CBA and residual anomaly using spectrum analysis method, were not able to detect the faults. Meanwhile, the faults can be detected in residual anomaly from TSA and upward continuation methods."

"Longsor merupakan salah satu bencana alam yang sudah menelan banyak korban mulai dari harta hingga nyawa. Sebagai upaya untuk mengurangi kerugian yang diakibatkan oleh bencana longsor, proses mitigasi bencana penting untuk dilakukan. Mitigasi yang akan dibahas beruspa identifikasi zona potensi kebencanaan menggunakan metode geofisika gaya berat dan penginderaan jarak jauh. Penelitian dilakukan di wilayah Sukabumi, Jawa Barat yang merupakan wilayah padat penduduk dan bagian dari Zona Bandung dan Zona Pegunungan Selatan menurut Van Bemmelen (1949). Metode yang digunakan adalah metode anomali gravitasi dengan analisis Second Vertical Derivative (SVD) dan analisis citra optik dengan klasifikasi Support Vector Machine menghasilkan peta pesebaran potensi longsor wilayah Kabupaten Sukabumi.

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Landslides are one of the natural disasters that have claimed many victims ranging from property to lives. In an effort to reduce losses caused by landslides, it is important to carry out disaster mitigation processes. Mitigation that will be discussed is in the form of identifying potential disaster zones using gravity geophysical methods and remote sensing. The research was conducted in the Sukabumi area, West Java, which is a densely populated area and part of the Bandung Zone and the Southern Mountain Zone according to Van Bemmelen (1949). The method used is the gravitational anomaly method with Second Vertical Derivative (SVD) analysis and optical image analysis with the Support Vector Machine classification to produce a map of the distribution of landslide potential in the Sukabumi Regency.

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