minimummagnitude

Minimum magnitude is a qualitative term used to describe the lowest magnitude value that is relevant for a particular dataset or observation. Magnitude, a logarithmic measure of intensity or brightness, is context-sensitive: in some fields it denotes the faintest detectable signal, in others it marks the brightest observed value. Consequently, "minimum magnitude" does not refer to a single universal constant, but rather to a threshold or extreme value chosen for analysis.

In seismology, Mmin denotes the smallest earthquake magnitude that a seismic network can reliably detect and locate. It depends on instrument sensitivity, network coverage, noise, and data processing. Mmin determines catalog completeness and affects the estimation of the frequency–magnitude distribution, often requiring statistical corrections if many events lie below the threshold. "Completeness magnitude" Mc is a related concept.

In astronomy, the apparent magnitude scale assigns smaller numbers to brighter objects. A survey or instrument has a limiting magnitude, typically the faintest detectable object, which is the maximum magnitude rather than minimum. However, when analyzing time-series photometry, the term "minimum magnitude" may describe the peak brightness reached by a variable star or transient, i.e., the lowest magnitude value observed.

In data analysis, minimum magnitude can serve as a detection threshold or selection criterion. Misestimating Mmin or mistaking a limiting magnitude for a true signal can bias statistical inferences, such as rate calculations or model fits. Properly characterizing the detection threshold and catalog completeness is essential for robust results.

See also: magnitude (astronomy), detection limit, completeness (statistics), Gutenberg-Richter law.