Geology Structure Identification Using Pre-Stack Depth Migration (PSDM) Method of Tomography Result in North West Java Basin

North West Java Basin is a tertiary sedimentary basin which is located in the right of the western part of the Java island. North West Java Basin is geodynamic where currently located at the rear position of the path of the volcanic arc of Java that is the result of the India-Australia plate subduction to the south towards the Eurasian plate (Explanation of Sunda) in the north. Geology structure observation is difficult to be conducted at Quaternary volcanicfield due to the classical problem at tropical region. In the study interpretation of fault structures can be done on a cross-section of Pre-Stack Depth Migration (PSDM) used prayer namely Hardware Key Device, ie Central Processing Unit: RedHat Enterprise Linux AS 5.0, prayer Monitor 24-inch pieces, Server: SGI altix 450/SuSe Linux Enterprise Server 9.0, 32 GB, 32 X 2,6 GHz Procesor, network: Gigabyte 1 Gb/s, and the software used is paradigm, product: Seismic Processing and Imaging. The third fault obtained in this study in accordance with the geological information derived from previous research conducted by geologists. The second general direction is northwest-southeast direction represented by Baribis fault, fault-fault in the Valley Cimandiri and Gunung Walat. This direction is often known as the directions Meratus (Meratus Trend). Meratus directions interpreted as directions that follow the pattern of continuous arc Cretaceous age to Meratus in Kalimantan.


Int r oduct i on
Geological structure observation is difficult to be conducted at Quaternary volcanicfield due to the classical problem at tropical region such as intensive erosion, dense vegetation covers, and rough terrain (Pradipta & Saepuloh, 2016). North W est Java Basin is a tertiary sedim entary basin w hich is located in the right of the w estern part of the Java island (Fig 1). Proven can produce hydrocarbons, such as Field Jatibarang. This basin has a distribution of land and offshore Serang in w est stretches Eastw ard to Cirebon and consists of Several sub-basins (Noble et al., 1997).
Research on seism ic previously perform ed using side scan sonar instruments for Identification seabed for introduction of seism ic (Lubis et al., 2017). North W est Java Basin is geodynam ic currently located at the rear position of the path of the volcanic arc of Java that is the result of the India-Australia plate subduction to the south tow ards the Eurasian plat e (Explanation of Sunda) in the north.
Several tectonic event s that have occurred since the Tertiary affect the form ation of the structure and patterns of sedim entation in the basin. During the period of Late Cretaceous to Early Eocene, ongoing subduction know n as the M eratus subduction on the southern boundary of the Sunda Shelf w ith fire m ountain trails pass through the North W est Java Basin (Arpandi & Patm osukismo, 1975).
The M eratus subduction affects the state geological basin (Gresko et al., 1995). The occurrence of regional m etam orphism in the Late Cretaceous, the Paleocene deform ation, and volcanism until the Early Oligocene estim ated of M aratus subduction-related activities. M etam orphism and m agm atism that took place result ed in m etam orphic and igneous intrusions are then com piled bedrock in North W est Java Basin, w hile the deform ation caused erosion on the appointm ent and Kala Paleocene. Regional stratigraphy basin of North W est Java are present ed in  PSDM results obtained in the last iteration of process tom ography (accurate velocity m odels result of im provem ents) can be used for further seism ic activity, nam ely the int erpretation. Subsurface fault identification, estim ation of reservoir thickness distribution, and calculation of hydrocarbon reserves is som e process of interpretat ion that can be done on a cross-PSDM .
Fi g 2. Regional stratigraphy basin of North W est Java (Adnan et al., 1991) Continuity of reflectors are sharper and can reduce the effect s of an excess pull-up im aging resulting from the process PSDM . Im age of PSDM result s m ore present than t he actual geological m odel generated imaging PSTM process. The process w ill be easier because t he int erpretation of the subsurface dom ain is already in depth (depth).
Fault or the fault is a fracture zone in t he rock that has undergone a shift both vertically and rotated so that the displacem ent betw een t he parts that deal. The shift of these rocks occur along a surface called the fault plane. Fault w as caused by unequal pressure on a layer of rock. The rock w ill undergo deformation w hen passing the threshold pow er of elasticity, these rocks w ill experience a fault or faults. (1) slip is a movem ent distance relative to one side against the other, (2) throw a vertical com ponent in the field of separation of fault, (3) heave a horizontal component in the field of separation of fault, (4) dip is the angle bet w een the fault plane w ith the horizontal plane, (5) hade an angle betw een the fault plane to t he vertical plane, and (6) fault trace a fault line on a surface. In principle, any fault on the seism ic data indicated by the loss of the seism ic event, diffraction, dip changes, and changes in t he pattern of events that pass through fault.

M at er i als and M et hod
In the study used prayer nam ely Hardw are Key Device, ie Central Processing Unit: RedHat Enterprise Linux AS 5.0, prayer M onitor 24-inch pieces, Server: SGI altix 450/SuSe Linux Enterprise Server 9.0, 32 GB, 32 X 2,6 GHz Procesor, netw ork: Gigabyte 1 Gb/s, and t he softw are used is paradigm, product: Seism ic Processing and Imaging, w ith details: (1) Softw are GeoDepth Velocity Modeling (Epos 41) The data consists of tw o types of seism ic data and w ell data. The seism ic data consists of CDP gathers dan RM S velocity and the w ell data covering: sonic log, density log, resistivity log, gam ma log ray (GR), and neutron log. The log data is used to calculate t he estim ation of hydrocarbon reserves.
The data in this study consists of three m ain activities, nam ely to m ake t he m ap a 3D m odel RM S velocity as in Fig. 3, m aking and repairing interval velocity m odel, and identify subsurface structure of the final PSDM results (Fig 4). Identification of the structure in this research focused on the structure of the fault or faults. Sufficient geological know ledge, especially know ledge is the basis of geological structure in identification of the fault. Faulting of PSDM cross section that has been identified, the next dipicking fault, then in the grid so it looks fault field.

Result and di scussi on
There are three pieces of fault that has been identified from the result s of the last tom ographic PSDM sesarnya fields (red, blue and purple) show n in Fig 6. Fault-fault produced already in the depth dom ain, m eaning there are in the depth of the actual fault. 3 pieces fault determ ination is based on the com ponents of the fault in general that fault plane, tactics (strike) fault, the slope of the fault, the hanging w all, foot w all, slip net (includes trike slip and dip-slip).    The third fault obtained in this study in accordance w ith the geological inform ation derived from previous research conducted by geologists. According to Martodjojo (2003), in general faults and folds in the basin of North W est Java is divided into three m ain directions (Fig 10). The first direction is southw est -northeast, w hich is represented by Cim andiri fault, reverse fault and fault -Rajam andala other faults in the area Purw akarta. This direction is often know n as the directions M eratus (M eratus Trend). The M eratus direntions w ere interpreted as directions that follow the pattern of continuous arc Cretaceous age to M eratus in Kalim antan (Katili, 1978 andSetiaw an et al., 2015). Fault corresponding to the first direction in this study is a norm al fault in blue and red (Fig 7 and 8).
The second general direction is northw estsoutheast direction represent ed by Baribis fault, faults in the Cim andiri valley and m ount W alat. This direction is know n as directions Sumatra (Sumatra Trend), as a parallel to t he direction of the Bukit Barisan M ountains. Fault that has been identified in accordance w ith the direction this is norm al fault purple color (Fig. 8). The third general direction is north-south direction. These directions are on-m ountain Ciletuh straightness Thousand (Fault Cidurian, block Leuw iliang). But in the Sunda Shelf, off t he northern coast of W est Java, the pattern of this fault is a m ajor pattern.

Conclusi on
Research in North W est Java Basin have third general direction is north-south direction. The third fault obtained in this study in accordance w ith the geological inform ation derived from previous research conducted by geologists.