To be most useful, an ideal definition would (a) be general to all exploration geophysics regardless of survey type and target, and (b) provide an interpretive link between an anomaly and its rock-made source. When all is said and done, what is an anomaly? And is an anomaly source generally a structure (item 5)? Is a geophysical anomaly the same as the geologic feature which is its source (items 1 and 5), or are these phenomena of different categories? Are only those anomalies deemed of exploration interest worthy of the title (item 6)? Why different anomaly definitions for different survey types? Some of these items seem to record colloquialisms (5), others are descriptive not definitional (7). But what do they add up to? Item 2 only seems to mathematize item 4, but 4 is unaccountably restricted only to gravity surveys. These specific points are useful, as far as they go. An interesting resistivity anomaly is generally smaller than background. In the frequency domain an anomalous region has a resistivity which decreases with frequency. An induced-polarization anomaly is usually positive and greater than background (or the normal effect) to be economically interesting. Especially, a deviation which is of exploration interest a feature which may be associated with petroleum accumulation or mineral deposit. Occasionally used for unexplained seismic events. In seismic usage, generally synonymous with structure. A gravity measurement which differs from the value predicted by some model, for example, a Bouguer or free-air anomaly (q.v.). A portion of a geophysical survey, such as magnetic or gravitational, which is different in appearance from the survey in general. A deviation from uniformity in physical properties a perturbation from a normal, uniform, or predictable field. Our exploration bible, the SEG dictionary (Sheriff, 1991), spake thus.Īnomaly. But because everyone is assumed to know, it seemed, many geophysics texts and reference books don’t even bother to offer a definition. In an appalling, guilty, dreadful chill of sudden horror at my own dismal ignorance, I got busy looking it up. what exactly? We say “anomaly” all the time.
Oil and mineral deposits are found in the rock mass, and we use geophysics to locate them.
The Earth is round not flat (we say today), or flat not round (we said a few centuries ago). The sun rises in the east and sets in the west. Some things seem so blindingly self-evident that no one bothers to examine them.
#Anomaly definition software
Meanwhile, a client wanted to know about EM anomalies on his mineral property, another asked if anomalies in a derivative magnetic map were real or processing artifacts, an oilman wondered if gravity anomalies might help to delineate a frontier basin, somebody else was giving a talk about separating intrasedimentary from intrabasement magnetic anomalies, a software vendor offered anomaly enhancement, and a voice on the phone enthused that seeing good anomalies in one 3-D seismic survey surely made up for finding none in the more expensive other. The disconcerting, blank silence that ensued was repeated by many subsequent senior classes in the following years, and at various schools. It began by accident, when I casually asked a class of fourth-year geophysics students to define the term anomaly.
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