Analysis of gravity anomalies with hyperbolic density contrast:
An application to the gravity data of Western Anatolia
Coşkun Sari and Müjgan Şalk
Dokuz Eylul University, Engineering Faculty, Dept. of Geophysics, 35100 Bornova-Izmir, Turkey
(Received 10 November 2001; accepted 11 January 2002)
Abstract:The primary objective of a gravity survey over a sedimentary basin is to delineate the shape of the basin. To fulfill this objective, information is needed about the densities within the sedimentary section. Densities of sedimentary rocks increase with depth (mainly due to compaction), approaching that of the basement in deep basins. Sedimentary basins are generally associated with low gravity values due to lower density of the sedimentary infill..Further, gravity modelling of a basin requires the use of expressions with hyperbolic density contrast concerning the anomaly produced by the model. The variation of the density of sediments with depth can be represented by a hyperbolic function. In this study, synthetic examples are presented to show the use of the closed form expression for the gravity anomaly of a two-dimensional arbitrarily shaped body with a hyperbolic density contrast
Tthe most pronounced structural and morphological features of western Anatolia are caused by E-W trending normal faulting which creates the boundaries of Büyük Menderes, Küçük Menderes and Gediz grabens. These grabens which have negative Bouguer gravity anomalies are filled with Neogen sediments. These anomalies, were interpreted using a hyperbolic density function, in order to determine the depths to the metamorphic basement. The approximate depth to the metamorphic basement at each observation point is calculated using the gravity formula on an infinite slab with hyperbolic density contrast. The maximum depth of Gediz graben are determined as 2 km and 1.8 km along two almost parallel profiles.Concerning the Büyük Menderes graben, The maximum depth was found 2.5 km.
Key Words: Gravity Anomalies, Hyperbolic Density Contrast,Western Anatolia.