3D-FTG Theory

Examples

The following examples aim at enhancing the different FTG components uses. Even if the vertical derivative Tzz is the more meaningful component, you will learn how to see and interpret the horizontal derivatives of the vertical component Tzx and Tzy, and even the horizontal components derivatives Txx and Tyy.
In each 3D-FTG response :

• Tzz locates target
• Txx and Tyy identify N-S and E-W edges of target
• Txz and Tyz identify central axes of target mass, highs and lows defining fault trends
• Txy shows anomalies associated with 'corners' of target

Tzz gradient data measures up-down changes in up-down gravity. Tzz represents the difference between the near and far response. It highlights all edges and is the easiest gradient to interpret directly. Geologic structure is usually evident in the data when large mass anomalies, such as salt, are present. Tzz gradient data combines Txx and Tyy gradients. It highlights all edges and is useful for understanding the approximate shape of the dominant mass anomaly.

Theoretical cube	Theoretical ellipse	Real salt dome
Tzz	Tzz	Tzz

Txx gradient data measures east-west changes in east-west gravity, whereas Tyy measures north-south changes in the north-south gravity. Txx and Tyy emphasizes north-south and east-west trending edges and images at a resolution comparable to seismic.

Txx	Txx	Txx
Tyy	Tyy	Tyy

Txz and Tyz gradient data delineates respectively the north-south and the east-west mass anomaly axis. It also helps show north-south and east-west trending edges. Notice that a positive mass anomaly gives rise to both positive and negative gradients values.

Txz	Txz	Txz
Tyz	Tyz	Tyz

You can click on the pictures below to have an overview of the 5 components for each example used in this page.

Theoretical cube	Theoretical ellipse	Real salt dome

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