PULL-APART GRABENS GEOMETRY ALONG THE SUMATRAN FAULT Dumex Pasaribu (1,2*), Benyamin Sapiie (1) and Indra Gunawan (1)
1) Institut Teknologi Bandung (ITB)
Jalan Ganesha 10, Bandung 40132, Indonesia
dumex.pasaribu[at]gmail.com
2) Universitas Pertamina (UPer)
Jalan Teuku Nyak Arief Simprug, Jakarta Selatan 12220, Indonesia
Abstract
This study conducted to determine the geometry of pull-apart grabens along the Sumatran Fault. As known that Sumatran Fault is a dextral strike-slip fault formed as a strain partitioning in parallel vector partition from oblique convergence on the subduction zone of the southwest edge of Sundaland. This fault forms a wrench system which at the bottom has a deep-seated sub-vertical fault plane to the old crystalline basement, while the shallower parts to the surface in some places form the flower structures. The negative flower structures along the Sumatran Fault produce pull-apart grabens and potentially acting as sedimentation basin that can be seen nowadays in Sumatran Fault zone.
The methodology in this study start with digital surface geological mapping on the Sumatran Fault wrench system using digital elevation model (DEM), bathymetry data, surface geological maps, combined with the seismicity maps, and data from the previous publications. The results of this digital surface mapping are determination of the pull-apart graben, calculation of the correlation of length to width of each graben. At least about 53 present day pull-apart grabens found, where there was one graben which was outlier and deformed due to volcanism.
The approach in determining the pull-apart graben is calculating in two dimensions using the ellipsoid formation, so that the length is the elongated axis and the width is another axis in the middle that perpendicular to the length. The calculation of the correlation of length (x) to width (y) shows a linear relationship, y = 0.2563x with R2 = 0.8389, generally means the length of the graben in the Sumatra Fault zone is four times its width.
