Lilik Hendrajaya

Fractal geometry of the sumatra active fault system and its geodynamical implications

Abstract The Sumatra active fault system is a 1650 km long northwest trending dextral active strikeslip fault which accommodates the oblique convergence between the Indo-Australian and the Eurasian plates. It consists of 11 fault segments connected northward to the Andaman extensional back arc basin and southward to the extensional fault zone of the Sunda Strait. The geometries of the 11 segments are quantified using a fractal approach and it is found that their fractal dimensions (D) range from 1.00 ± 0.03 to 1.24 ± 0.03. Larger D values are associated with more irregular fault geometry. There are six discontinuities, reflected by sharp changes of fractal dimensions, observed along the segments. The locations of the discontinuities correspond to sites of major structural breaks in Sumatra mainland and its fore arc and back arc. The discontinuities and variations of D values suggest that the Sumatra mainland is not rigid. Instead it appears to be segmented into several blocks which may correlate to the segmentation in the Sumatra fore arc. This segmentation may explain the large discrepancy among the displacements and velocities of the Andaman Sea opening, the Sumatra fault motion and the Sunda Strait opening. This research also demonstrates the applicability of the fractal approach for analyzing the variations of fault geometry due to geodynamic processes.

Reservoir fluid identification and elastic modulus determination using AVO

Abstract AVO analysis based on the increase of reflected amplitude with increasing distance between source and receiver. This anomaly has been proved to be useful for gas identification from seismic data. A specific inversion technique has been developed to estimate the Poissons ratio from AVO anomaly. It based on the Shuey (1985) formula and the implementation of generalized linear inversion proposed by Marquardt (1963). The technique adjusts the convergence of the iterative process in order to find the unknown parameters by considering the available observed data. Once the Poissons ratio is obtained, the velocity of the S wave can be estimated and the elastic properties of the reservoir rock such as Youngs modulus can be derived. Application of this technique to a limestone reservoir of the Cicauh area in the North West Java Basin gives the value of Youngs modulus of about 23392 MPa. The porosity which derived from this value was 36.6% which is very close to well data. According to the Wren (1984) diagram the P wave velocities of 2700–3550 m/s correspond to reservoir rocks of sandstone containing fluid. In fact according to the well data, it is a limestone containing gas. Therefore, a special diagram showing the relationship between P wave velocities and Poissons ratios should be developed. It will be useful in identification of reservoir fluid by means of AVO before drilling.

ANALISIS PENUMBUKAN BOLA BAJA TERHADAP MATERIAL BUTIRAN DALAM SILINDER BERPUTAR

Abstrak Tumbukan antara bola baja dengan material dimanfaatkan dalam proses penghancuran material butiran. Proses penghancuran tersebut terjadi di dalam silinder yang dinamakan dengan raw mill . Tabung ini diisi dengan bola baja dengan ukuran 6,5 mm dan diputar pada porosnya. Akibat perputaran tersebut dapat menghasilkan beberapa mode gerak. Mode gerak yang diinginkan adalah mode cataracting dan cascading . Kedua mode gerak ini sangat mendukung dalam proses penghancuran dan penghalusan material. Penelitian dilakukan dengan membuat miniatur raw mill yang berupa silinder yang berjari-jari 40 cm dengan tebal 3 cm. Perbandingan antara miniatur raw mill dengan sesungguhnya adalah 1:13,75. Dinding silinder dibentuk bergerigi dengan ketinggian gerigi 4 mm. Data yang diambil yaitu jumlah putaran silinder dan massa butiran material yang diumpankan ke dalam silinder. Data tersebut digunakan untuk estimasi energi rata-rata penumbukan dari bola baja terhadap material. Kata-kata kunci: bola baja, cataracting, cascading. Abstract The collision between the steel balls to the material used in the process of destruction of the granular material. The destruction process occurs in the cylinder whose called the raw mill. This tube is filled with steel balls with a size of 6,5 mm and rotated on its axis. As a impact of the rotation can produce some modes of motion. The desired motion mode is cataracting and cascading. Both modes of motion are very supportive in the process of crushing and refining material. Research carried out by making a miniature raw mill in the form of a cylinder with radius 40 cm and 3 cm of thickness. The comparison between the raw mill with a real miniature is 1:13,75. Serrated cylindrical wall formed with a height of 4 mm serrations. The data was taken are the number of dials and granular mass of material that is dive into the cylinder. The data is used to estimate the average energy comminuting of steel balls against the material. Keywords : steel balls, cataracting, cascading.

Landslide hazard and risk assessment for Ambon city using landslide inventory and geographic information system

Ambon Island is a volcanic islands arc and included in the territory of the archipelago of small islands are associated with subduction zones that have a degree of high vulnerability to natural disasters, such as erosion and landslides on the slopes of certain conditions. Landslides that occur various in the city of Ambon, usually occurs during the rainy season so that the impacts that occur not only occurs on site but also off site with amount of large sedimentation. This paper presents the application of digital image analysis techniques and tools Geographic Information Systems to describe the degree of landslide hazard and risk areas in locations Ambon City, Moluccas. The cause of the landslide is analyzed through various thematic layers attribute data for the study area. Landslide hazard zonation assessment is done by using historical data, while the landslide risk analysis is done by using the results of landslide hazard assessment and socioeconomic factors by using geospatial models. The risk assessment of landslides can be used to estimate the risk to the population, property and infrastructure. The study results in the form of a map of landslide hazard and the risk of landslides that act to support urban spatial planning based on disaster mitigation.

Geophysical education in Indonesia

Indonesian geophysicists obtain their first degrees in geophysics, physics, meteorology, geology, mathematics, or engineering. As they enter the workforce, they usually undergo practical geophysical training patterned after the needs of their employers. Job requirements range from acquisition to interpretation and everything in between. Research institutions and universities also offer opportunities.

Estimation of Parigi Reservoir Characteristics Using Seismic Attributes, AVO Analysis And AVO Inversion, And Seismic Inversion

In the carbonate reservoir, the gas was trapped in the cavity of the formation. First of all, to identify the cavity as the distribution of the cavity or porous zone will be done by reflection strength and instantaneous frequency from the seismic attribute analysis. After the zone has been identified, the existing gas and the value of porosity can be estimated using AVO analysis and AVO inversion technique. This idea was applied to the carbonate reservoir within the Parigi Formation in the Northwest Java Basin (Indonesia) by Santoso et al.( 1995). The result shows a clear zone of high reflection strength and low instantaneous frequency in the carbonate build up, The porosity estimated by AVO inversion gives a value of the porosity about 38% and the Poisson’s ratio arround 0.22 0.26. This paper is continuation of Santoso et al. (1995) study. It is done by the delineation of the porosity which can be displayed by the acoustic impedance section as a result of seismic inversion process. The delineation of the reservoir characters to the horizontal direction as previous study gives arround a similar value as shown by acoustic impedance value. When these results were compared to the borehole data in the location, the are very close. Therefore this idea has given a satisfactory result in estimating porosity from seismic data and delineating the carbonate reservoir away from the borehole. GEOLOGY OF PARIGI FORMATION