By : Dr. Agung Setianto, S.T., M.Si. and Dr. Ibrahim Djamaluddin
The ground motion prediction from specific seismic source faults plays an important role in prevention of earthquake disasters. The three-dimensional (3D) fault at subsurface layer provides spatial information on underground characteristics by the factor of the geometry of faults such as depth, width, dip and strike direction which defined from the base information by engineering measure on the ground surface. In this paper, the geoprocessing method by specified algorithm process within Geographic Information System (GIS) technology has been developed for creating a 3D fault layer to be applied in all faults, simultaneously. In this geoprocessing method, the geometry of 3D polygon data structure as 3D fault layer is derived from the geometry of polyline data structure as fault lines. The fault lines were determined usually by referring to the lineaments. Besides, the fault information such as fault dip and depth was obtained from ground measurement. The algorithm process for the geometrical transformation from surface lines into 3D polygons was applied by the geoprocessing method, automatically. A method to estimate the 3D fault layer with a higher accuracy was divided into 3 steps: a) the fault’s depth and width was not uniform, therefore proposed a topography classification of lineaments were conducted using the topographical data as first step; b) the classified topographical geometric fault’s were analyzed by the transformation of the geometry from the boundary of polylines into the 3D polygons using the dip and strike orientation in the GIS projection system; and c) finally, the transformed boundary of 3D polygons were converted into GIS shapefile of 3D polygons referring to the topographical surface elevation. As the investigation of the capability of this method, the lineaments in the designed area were evaluated by modeling the 3D fault layers. This method provided the 3D fault databases within GIS in the consideration for the regional ground motion prediction. Furthermore, the 3D fault database was applied by the GIS method to the ground motion prediction simulation.