bvärde

The b-value, or b-värde in Swedish, is a statistical parameter of the Gutenberg–Richter law that describes how earthquake frequencies decline with increasing magnitude. The law is commonly written as log10 N(M) = a − bM, where N(M) is the number of earthquakes with magnitude at least M, and a and b are constants. The slope b reflects the relative abundance of small versus large earthquakes. In many regions, b is around 1.0, but it varies with tectonic setting and time.

Estimating the b-value requires a complete and consistent earthquake catalog above a magnitude of completeness Mc. The most common method is maximum likelihood estimation. Factors that influence the value include the magnitude scale used (local, moment), the choice of Mc, aftershock sequences, data gaps, and the time window considered.

Interpreting b-values helps assess seismicity: a higher b-value indicates a relatively larger proportion of small earthquakes, while a lower b-value suggests relatively more large events. Changes in b-value over time can relate to changing stress conditions, aftershock productivity, or volcanic and tectonic processes. The concept is widely used in seismic hazard assessment and monitoring.

Limitations include sensitivity to catalog completeness, magnitude type, and non-stationarity; biases can arise from aftershocks or nonuniform sampling. Researchers report b-values with uncertainties and consult multiple methods to validate estimates. The term is used primarily in seismology and geophysics, often in conjunction with the Gutenberg–Richter relationship.