The Grindulu Fault is a one of the fault that lies alongside the Pacitan Regency, East Java. This fault is a land geological structure that is potential to be the source of earthquake disaster. The structure interpretation is carried out using gravity data by performing spectrum analysis and derivative methods to get a better understanding of the Grindulu Fault. We used gravity data from GGMplus. Spectrum analysis is performed by using Fourier transform to the bouguer anomaly. This Spectral Analysis generates a depth estimation of Grindulu Fault Zone anomaly source. Analysis of derivative methods provides information regarding the location of the fault anomaly source and information about the type of fault. Based on the result of spectral analysis, Grindulu Fault anomaly source is estimated to be at the upper limit of 160 meters and the lower limit up to 2897 meters. The Grindulu fault is interpreted to be segmented into at least 7 parts which is consisted of normal and reverse fault segmentations.
This research was aimed to determine the distribution pattern of magnetic field anomaly and to identify the lithology of underground structure in Bribin Karst using geomagnetic method. Research location was Semanu Sub-district, Gunungkidul Regency at UTM coordinate of 464061 mT-464929 mT and 9111097 mU-9111970 mU. The data were taken using G-5 Proton Precession Magnetometer (PPM) by looping method. The result showed that the distribution pattern of the magnetic field anomaly in Karst Bribin has value of 330 nT - 530 nT and anomaly values reflecting the system of Bribin River has value of 400 nT-460 nT. The lithology of underground structure in Karst Bribin has susceptibility value of -0.069 (in SI) - 0.0661 (in SI) with depth 200 m associated with limestone, tuff, gypsum, rock salt, and minerals calcite and anhydrite and the lithology associated with the system of Bribin River has susceptibility value -0.069 (in SI) associated with gypsum, rock salt, and minerals anhydrite.
Lamongan Volcano located in, East Javahas basaltic cinder or spatter cones and maars.The presence of maar and cinder cones indicates active volcanic activity at their time.We used secondary gravity data from GGMplus. The result of residual anomaly map shows that Maar which is located on the NW of Lamongan Volcano shows a lineament pattern with Lamongan Volcano which is trending northwest-southeast and maar indicates a normal fault.
Provinsi Maluku Utara terutama Pulau Halmahera dan sekitarnya merupakan bagian dari kerangka sistem tektonik Indonesia yang kompleks dan memiliki aktifitas tektonik yang tinggi. Daerah ini berada pada zona pertemuan lempeng Eurasia, lempeng Pasifik, lempeng Indo-Australia dan lempenglempeng kecil lainnya seperti lempeng Filipina. Sebagai akibat dari geodinamika maka daerah penelitian merupakan daerah dengan aktivitas seismisitas yang cukup tinggi, faktor utamanya karena terdapat struktur geologi berupa antiklin, sinklin, sesar naik, sesar mendatar dan sesar normal akibat aktivitas lempeng di daerah ini. Salah satu metode yang dapat digunakan untuk mengidentifikasi sesar dan jenisnya adalah metode gravitasi. Pada penelitian ini data yang digunakan adalah data observasi gravitasi satelit Topex dengan luasan area penelitian adalah 3.891,62 km 2 dalam bentuk Free Air Anomaly (FAA). Kemudian dikoreksi bouguer dan koreksi medan menghasilkan Anomali Bouguer Lengkap (ABL). Anomali regional dan residual menunjukkan korelasi yang baik dengan peta geologi daerah penelitian dalam mendeliniasi sebaran sesar dengan rentang nilai anomali positif ± 187 mGal dan anomali negatif ± -14.8 mGal. Analisis anomali Second Verticael Derivative (SVD) menunjukkan sebaran sesar di daerah penelitian adalah jenis sesar turun atau sesar normal.KATA KUNCI: anomali SVD, free air anomaly (FAA), koreksi bouguer, koreksi medan, sesar normal ABSTRACT−North Maluku, especially Halmahera Island is part of the framework of Indonesia's complex tectonic system and has a high tectonic activity. This area has the meeting zone of the Eurasia plate, the Pacific plate, the Indo-Australian plate and other small plates such as the Philippine plate. As a result of geodynamics, the research area with high seismic activity is due to many geological structures such as anticlines, synclines, upward faults, horizontal faults and normal faults due to plate activity in this area. One of the methods that can be used to identify the faults and their types is the gravity method. this study was using the gravitational observation data of the Topex satellite with an area of 3,891.62 km 2 in the form of Free Air Anomaly (FAA), which is then corrected by bouguers and field correction yields a complete Bouguer Anomaly (ABL). Regional and residual anomalies show the good correlation with the geological map of the study area in delineating the distribution of faults with a range of positive anomalies ± 187 mGal and negative anomalies ± -14.8 mGal. Second Vertical Derivatif (SVD) anomaly analysis shows that the distribution of faults in the study area is a type of normal fault.
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