Analysis of the magnitude-frequency distribution for the 1983–1984 earthquake activity of Campi Flegrei, Italy

Abstract

The magnitude-frequency distribution of earthquakes is one of the statistical relationships most frequently used to study the seismicity of a region. In this paper the Gutenberg-Richter frequency magnitude relationship is applied to the 1983–1984 earthquake sequence of Campi Flegrei, Italy, in order to estimate the space-time variation of the b-value, and its possible correlation with other geophysical parameters in the sequence. The investigated region has been divided into three areas on the basis of differences in seismic activity: (a) to the west of Pozzuoli, where seismicity occurred mostly as swarms; (b) to the east of Pozzuoli, where events mostly included single, high-energy earthquakes; and (c) in the western sector of the Gulf of Pozzuoli. Moreover, b-value estimates have been carried out according to different hypocentral depths of all seismic events in the sequence. The obtained results have shown strong depth variations of the b-value which might reflect important differences in failure conditions at different depths. Furthermore, a certain complexity in the shape of the obtained distribution functions n( M) has been pointed out. Temporal variations of b-value, computed both for the whole region and the different selected areas, seem to be meaningful because they do not depend on the number of shocks ΔN, the data overlap and the magnitude step ΔM. The rates of change of b-value Δb/ Δt, compared with the changing rates of seismic energy release ΔE/ Δt do not show a consistent correlation, hence the Δb/ Δt curve cannot be interpreted as a precursor to the other in any systematic way.