Changes

[[file:using-magnetics-in-petroleum-exploration_fig14-9.png|300px|thumb|{{figure number|2}}A series of four northeast-trending magnetic anomalies on the west (two highs, two lows) abruptly loses amplitude along a northwest-trending line (A–A′) that crosscuts them.]]

[[file:using-magnetics-in-petroleum-exploration_fig14-9.png|300px|thumb|{{figure number|2}}A series of four northeast-trending magnetic anomalies on the west (two highs, two lows) abruptly loses amplitude along a northwest-trending line (A–A′) that crosscuts them.]]

There is a fairly reliable way to determine the direction of throw of certain [[basement]] faults from magnetic maps. Faults that vertically offset basement or other magnetic sources generally show abrupt amplitude changes of magnetic anomalies, both the highs and lows. In [[:file:using-magnetics-in-petroleum-exploration_fig14-9.png|Figure 2]], a series of four northeast-trending magnetic anomalies on the west (two highs, two lows) abruptly loses amplitude along a northwest-trending line (A–A′) that crosscuts them. The high and low magnetic trends can be identified easily on both sides of this obvious down-to-the-east fault. The four anomalies disappear altogether along another northwest-trending line farther east (B–B′). This may be a strike-slip fault, which is not common in this area, or another down-to-the-east fault that has down-dropped the four anomalies beneath the level of detection—the preferred interpretation.

There is a fairly reliable way to determine the direction of throw of certain [[basement]] faults from magnetic maps. Faults that vertically [[offset]] basement or other magnetic sources generally show abrupt amplitude changes of magnetic anomalies, both the highs and lows. In [[:file:using-magnetics-in-petroleum-exploration_fig14-9.png|Figure 2]], a series of four northeast-trending magnetic anomalies on the west (two highs, two lows) abruptly loses amplitude along a northwest-trending line (A–A′) that crosscuts them. The high and low magnetic trends can be identified easily on both sides of this obvious down-to-the-east fault. The four anomalies disappear altogether along another northwest-trending line farther east (B–B′). This may be a strike-slip fault, which is not common in this area, or another down-to-the-east fault that has down-dropped the four anomalies beneath the level of detection—the preferred interpretation.

==Interpreting shear zones==

==Interpreting shear zones==