Magnetics
Magnetic surveys look for and map variations or “anomalies” in the strength and orientation of the earth’s magnetic field
These anomalies represent variances at specific points between measured values and the values predicted by a mathematical model of the earth’s magnetic field called the “magnetosphere.”
Rocks, in varying degrees, can be magnetized by the earth’s magnetic field through induction. Variations in the degree and direction of magnetization account for magnetic anomalies. Consequently, anomalies can say quite a bit about the lithology and depth of rock at a given location.
Sedimentary rock is, by orders of magnitude, less susceptibility to magnetization than igneous rock or metamorphic rock. As a result, variations observed in magnetic surveys are generally an expression of the underlying, usually igneous, basement rock. Because of this, magnetic data can be used to determine the depth of the basement rock. This in turn can tell us the thickness of the overlying sediments.
Close-sampled high-resolution magnetic survey data produce interpretations with finer-detailed, more structural variations at basement level and higher resolution within the sedimentary section. Magnetic analysis requires extensive knowledge of the different types of data available, the tools used to process or condition the data, and the presentation of the magnetic data for meaningful interpretations.