New methods for depth determination to horizontal cylinder
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ORIGINAL PAPER
New methods for depth determination to horizontal cylinder Fitian R. Al-Rawi
Received: 23 April 2012 / Accepted: 5 September 2012 # Saudi Society for Geosciences 2012
Abstract Three procedures can be utilized to determine the depth to the center of the horizontal cylinder from gravity profile. Firstly, the gravity profile is subjected to a simple filtering technique. Then, the maximum slope lines are drawn along the flanks of the filtered profile. The horizontal distances between the two slope lines for the positive part are measured at various amplitude levels. A plot of the horizontal distances against amplitude values will give an inclined straight line. The first procedure of depth estimation consists of measuring the distance between the points of intersection of the maximum slope lines at zero level background. This distance, for the positive or negative part, after it is multiplied by the empirical factor, gives directly the depth to the center of the horizontal cylinder. The other two procedures involve fitting a least square line to the inclined straight line of horizontal distances against amplitude values. Then, the maximum amplitude value of the filtered profile multiplied by an empirical factor is used to determine the depth, either graphically or through a simple equation. Accurate results have been achieved with low error percentages for a large number of gravity profiles due to synthetic horizontal cylinders having various depths and radii. Keywords Depth estimation . Gravity anomaly . Horizontal cylinder . Simple procedure Introduction One of the most important exploration problems is estimating the shape and depth of buried structures. The depth to simple geometric sources such as a sphere, horizontal cylinder, and vertical cylinder has been widely used which approximate equivalence is sufficient to determine whether the form and F. R. Al-Rawi (*) Department of Geology, College of Science, Baghdad University, Baghdad, Iraq e-mail: [email protected]
magnitude of the calculated gravity effect are close enough to those observed to make geophysical interpretation reasonable. There are several depth rules (Telford et al. 1990; Reynolds 2003) that can be used to determine a body’s depth. Simplification of analytical solutions due to simple geometric bodies is commonly used to obtain an approximate of the body’s depth. The most common rule of thumb, concerns the use of the half width of the anomaly to determine the depth to the center of horizontal cylinder (Nettleton 1976). The wellknown form of equation for depth estimation for horizontal cylinder (depth0half width) has been derived and mentioned in most geophysical books (Dobrin 1976; Sharma 1986; Robinson and Coruch 1988). Several methods have been developed to interpret gravity data using a fixed simple geometry. These methods include Fourier transform (Odegard and Berg 1965), least square minimization approaches (Abedelrahman and Sharafeldin 1995) and Euler deconvolution technique (Zhang et al. 2000). These methods all require
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