INTERPRETASI STRUKTUR GEOLOGI PADA AREA GEOPARK CILETUH DENGAN ANALISIS DERIVATIF DATA GAYABERAT GGMPLUS

Geopark Ciletuh terletak di Kecamatan Ciemas sebelah barat Kabupaten Sukabumi, Jawa Barat, Indonesia. Pada Geopark Ciletuh terdapat adanya batuan Pra-Tersier yang tersingkap di permukaan dan juga terdapat berbagai macam struktur yang terbentuk akibat terjadinya pergerakan tektonik di sebelah barat daya Geopark Ciletuh. Penelitian ini dilakukan bertujuan mendelineasi struktur pada Geopark Ciletuh yang timbul oleh adanya perbedaan densitas dengan metode gaya berat. Pada penelitian ini digunakan analisis derivatif first horizontal derivative (FHD) untuk mengetahui keberadaan struktur dan second vertical derivative (SVD) untuk menentukan jenis patahan. Pada penelitian ini juga dilakukan dip estimation dengan metode multi-level second vertical derivative (ML-SVD). Setelah didapatkan data FHD, SVD, dan ML-SVD selanjutnya diintegrasikan dengan data geological section dari peta geologi Lembar Jampang Balekembang untuk dibuat penampang geologi. Interpretasi dugaan patahan memiliki arah orientasi NW-SE dan NE-SW. Hasil penelitian menujukkan adanya indikasi dugaan patahan naik dan patahan turun. Pada analisis terpadu, didapatkan adanya kesesuaian maupun ketidakkesesuaian antara data peta geologi dengan data geofisika.

NORMALIZED VERTICAL DERIVATIVES IN THE EDGE ENHANCEMENT OF MAXIMUM-EDGE-RECOGNITION METHODS IN POTENTIAL FIELDS

Gravity and magnetic data have unique advantages for studying the lateral extents of geological bodies. There is a class of methods for edge recognition called the maximum-edge-recognition methods that use their extreme values to locate the edges of geological bodies. These methods include the total horizontal derivative, the analytic signal amplitude, the theta map, and the normalized standard deviation. These are all first-order derivative-based techniques. There are also higher-order derivative-based methods that are derived from the first-order filters, for example, the total horizontal derivative of the tilt angle. We present an edge recognition filter that is based on the idea of the normalized vertical derivatives of existing methods. For each maximum-edge-recognition method, we first calculate its nth-order vertical derivative and then use thresholding to locate its peaks. The peak values are subsequently normalized by the values of the original maximum-edge-recognition method. Testing on synthetic and real data shows that the normalized vertical derivatives of the maximum-edge-recognition methods have higher accuracy, better lateral resolution and are more interpretable than existing techniques, and thus are a worthwhile addition to the set of edge-detection tools for potential-field data.

Structural interpretation of High-resolution aeromagnetic data over the Dahomey basin, Nigeria: implications for hydrocarbon prospectivity

The renewed quest to boost Nigeria’s dwindling reserves through aggressive search for oil and gas deposits in Cretaceous sedimentary basins has re-ignited the need to re-evaluate the hydrocarbon potentials of the Dahomey Basin. Aeromagnetic data are a low-cost geophysical tool deployed in mapping regional basement structures and determination of basement depths and sedimentary thickness in frontier basin exploration. In this study, high-resolution aeromagnetic (HRAM) data covering the Dahomey Basin Nigeria have been interpreted to map the basement structural configuration and to identify mini-basins favorable for hydrocarbon prospectivity. The total magnetic intensity grid was reduced to the equator (RTE) and edge detection filters including first vertical derivative (FVD), total horizontal derivative (THDR), tilt derivative (TDR) and total horizontal derivative of upward continuation (THDR_UC)) were applied to the RTE grid to locate the edges and contacts of geological structures in the basin. Depth to magnetic sources were estimated using the source parameter imaging (SPI) method. Data interpretation results revealed shallow and deep-seated linear features trending in the NNE-SSW, NE-SW, NW-SE and WNW-ESE directions. The SPI map showed a rugged basement topography which depicted a horst-graben architecture on 2D forward models along some selected profiles. Two mini-basins ranging in basement depths between 4.5 – 6.3km were mapped offshore of the study area. It appears the offshore Dahomey Basin holds greater promises for hydrocarbon occurrence due to the presence of thicker succession of sedimentary deposits in the identified mini-basins.

A regularity criterion for liquid crystal flows in terms of the component of velocity and the horizontal derivative components of orientation field

<abstract><p>In this paper, we establish a regularity criterion for the 3D nematic liquid crystal flows. More precisely, we prove that the local smooth solution $ (u, d) $ is regular provided that velocity component $ u_{3} $, vorticity component $ \omega_{3} $ and the horizontal derivative components of the orientation field $ \nabla_{h}d $ satisfy</p> <p><disp-formula> <label/> <tex-math id="FE1"> \begin{document}$ \begin{eqnarray*} \int_{0}^{T}|| u_{3}||_{L^{p}}^{\frac{2p}{p-3}}+||\omega_{3}||_{L^{q}}^{\frac{2q}{2q-3}}+||\nabla_{h} d||_{L^{a}}^{\frac{2a}{a-3}} \mbox{d} t&lt;\infty,\nonumber \\ with\ \ 3&lt; p\leq\infty,\ \frac{3}{2}&lt; q\leq\infty,\ 3&lt; a\leq\infty. \end{eqnarray*} $\end{document} </tex-math></disp-formula></p> </abstract>

Pemodelan Inversi 3D Daerah Panas Bumi Berbasis Data Anomali Magnetik di Kota Agung dan Sekitarnya, Provinsi Lampung

Penelitian tentang pemodelan 3 Dimensi berbasis data anomali magnetik untuk mengetahui struktur bawah permukaan telah dilakukan di Kabupaten Tanggamus dan Kabupaten Lampung Barat. Data yang digunakan adalah data sekunder yang diambil dengan cara mendigitasi peta anomali magnet total. Pemisahan anomali regional, analisis turunan mendatar pertama (First Horizontal Derivative), dan pemodelan inversi 3D telah dilakukan untuk mencapai tujuan dari penelitian ini. Hasil penelitian menunjukkan bahwa daerah penelitian memiliki potensi panas bumi yang cukup besar di sekitar Kota Agung dan Gunung Sermaun dengan Sebaran nilai anomali magnetik dari -362,7 nT hingga 602,4 nT. Hasil analisis turunan mendatar pertama menunjukkan adanya beberapa patahan yang diduga sebagai jalur bagi fluida panas untuk mengalir ke permukaan. Hasil pemodelan inversi 3D menunjukkan struktur lapisan bawah permukaan Kota Agung bahwa reservoir panas bumi terdapat pada kedalaman 3000 meter, berupa batu pasir, batu lempung, batu lanau, dan batuan yang mengandung mineral non magnetik dengan rentang nilai -0,005 SI hingga -0,002 SI.

Studi Identifikasi Struktur Geologi Bawah Permukaan Untuk Mengetahui Sistem Sesar Berdasarkan Analisis First Horizontal Derivative (FHD), Second Vertical Derivative (SVD), Dan 2,5D Forward Modeling Di Daerah Manokwari Papua Barat

In general, Manokwari has a geological structure that is in the form of a folding area found in the highlands of the mountains. Among the creases, there is a fault up and the fault down. In coastal or marine areas found many reefs and corals. The study of gravity was conducted in the Manokwari area of West Papua with the aim to know the subsurface geological structures based on FHD (First Horizontal Derivative), SVD (Second Vertical Derivative) and 2.5D Forward Modeling on the residual anomaly maps of the study area. The results showed that the research area has Bouguer Anomaly value ranged from 4 mGal to 96 mGal with the low anomaly at the left side of the research area lengthwise relatively in north-west to south-east direction, the middle-value anomaly spreads in the west-east area of research area, high anomaly scattered in the northern part of the research area. The results of the 2.5D subsurface modeling and the SVD and FHD analysis indicated the presence of a Thrust Fault on the C-C’ cross-section, on the B-B’ cross-section there is a Diorite Lembai intrusion with the density value is 2.75 gr/cc, whereas the A-A' cross-section which intersects with Sorong fault were not found any fault or rock intrusion based on observed gravity data of the research area.

Identifikasi Potensi Sistem Panasbumi Berdasarkan Korelasi Data Geologi Dan Data Gravitasi Dengan Menggunakan Teknik Filtering First Horizontal Derivative (FHD) - Second Horizontal Derivatif (SVD)

Daerah panasbumi “Z” dalam tatanan tektoniknya termasuk pada jalur back-arc Sumatera, tepat pada salah satu segmen sesar Sumatera bagian selatan, disusun oleh batuan vulkanik dan sedimen klastik yang berumur Tersier hingga Kuarter (Andesit-Basalt). Gejala adanya potensi sistem panasbumi pada daerah penelitian ditandai dengan kemunculan manifestasi permukaan berupa alterasi dan lima mata air panas bersuhu 44,4 – 92,5 oC dan pH antara 8,19 – 9,43. Pengolahan Data gravitasi menggunakan teknik pemisahan Complete Bouguer Anomali (CBA), filtering First Horizontal Derivative (FHD) dan filtering Second Vertical Derivative (SVD) untuk mengetahui kemungkinan lokasi sumber panas dan letak bidang kontak terjadinya anomali serta jenis sesarnya. Berdasarkan slicing lintasan FHD dan SVD, struktur pada peta geologi didominasi oleh sesar naik dan sesar normal yang bersifat regional, serta struktur dengan kompleksitas tinggi yang bersifat lokal. Kemunculan manifestasi permukaan sistem panasbumi berada disekitar nilai anomali residual gravitasi tinggi (8 – 24 mgal) yang mengindikasikan terdapatnya batuan yang kompak dan massif. Diperkirakan sistem panasbumi daerah penelitian termasuk jenis tektonik fracture zone serta anomali tinggi yang berada di sekitar APZ1-APZ2-APZ3 tersebut terdapat batuan intrusi yang berperan penting sebagai sumber panas.

IDENTIFICATION OF BURIED ARCHEOLOGICAL OBJECTS WITH RADIAL DERIVATIVES OF MICRO GRAVITY DATA

The development of recent gravimetric technology allows us to measure gravity anomalies with accuracy of micro Gal. Micro gravity is able to detect very small gravity anomalies such as anomaly due to buried archeological objects below the earth surface. Radial Derivatives of gravity data is used to sharpen anomaly due to lateral changes of density contrast. Horizontal derivatives carried out by previous researchers have some weaknesses, i.e. the loss of derivative values in certain directions and inconsistence values at the source boundary of the same anomaly edge. To solve the horizontal derivative problem, a radial derivative is made. Radial derivative is derivative of gravity anomaly over horizontal distance in the radial direction from a certain point which is considered as the center of anomaly. There are two kind of radial derivative i.e. First Radial Derivative (FRD) and Second Radial Derivative (SRD). Blade Pattern is another way to enrich the ability of SRD to detect boundary of anomaly source. Synthetic gravity data of buried archeological object was made by counting the response of forward modelling. All of programs and calculation of the models in this research is performed based on Matlab® program. The results of the tests on the synthetic data of the model show that the radial derivative is able to detect the boundaries in buried temples due to density contrast. The advantage of radial derivatives which is a horizontal derivative in the direction of radial compared to ordinary horizontal derivatives is the ability to detect vertical boundaries of various anomaly due to horizontal layers and capable of showing density contrast in almost all directions.