Changes

==Elevation change due to a fault==

==Elevation change due to a fault==

[[file:using-magnetics-in-petroleum-exploration_fig14-6.png|left|thumb|{{figure number|1}}]]

[[file:using-magnetics-in-petroleum-exploration_fig14-6.png|300px|thumb|{{figure number|1}}Hypothetical cross section demonstrating that basement rock has the same susceptibility across the fault.]]

The presence of a fault is a common interpretation of a magnetic increase or decrease. This interpretation assumes the fault throw, which changes the elevation to the top of basement, is the cause of the anomaly. It also assumes uniform lithology and uniform magnetic susceptibility of basement across a fault. Given this (usually incorrect) assumption, we can calculate the depth of the fault and its throw from the shape and amplitude of an observed magnetic curve. If we do not know the exact susceptibility, we can calculate a series of curves to establish a range of probable values of the throw. In all cases, the magnetic high necessarily appears on the upthrown side of the fault.

The presence of a fault is a common interpretation of a magnetic increase or decrease. This interpretation assumes the fault throw, which changes the elevation to the top of basement, is the cause of the anomaly. It also assumes uniform lithology and uniform magnetic susceptibility of basement across a fault. Given this (usually incorrect) assumption, we can calculate the depth of the fault and its throw from the shape and amplitude of an observed magnetic curve. If we do not know the exact susceptibility, we can calculate a series of curves to establish a range of probable values of the throw. In all cases, the magnetic high necessarily appears on the upthrown side of the fault.

In the hypothetical cross section in [[:file:using-magnetics-in-petroleum-exploration_fig14-6.png|Figure 1]], basement rock has the same susceptibility across the fault.

In the hypothetical cross section in [[:file:using-magnetics-in-petroleum-exploration_fig14-6.png|Figure 1]], basement rock has the same susceptibility across the fault.

==Lithologic changes due to a fault==

==Lithologic changes due to a fault==