Magnitude formulae and intensity-magnitude relations for early instrumental earthquakes in the iberian region

The magnitudes of early instrumentally recorded earthquakes in the Iberian region (1912-1962) have been studied through processing of digitized seismo grams of Wiechert seismograph and analysis of macroseismic information. A m agnitude system based on instrumental registrations and macroseismic observ ations has been proposed. It consists of two compatible magnitude formulae depending on the total duration of seismic oscillations and on the maximum ground amplitude/period ratio of surface waves and includes correspondent i ntensity-magnitude relationships.