Recalibration of the Magnitude Scales at Campi Flegrei, Italy, on the Basis of Measured Path and Site and Transfer Functions

Abstract

Abstract New duration-based local ( M L ) and moment ( M w ) magnitude scales are obtained for the Campi Flegrei area through analysis of a dataset of local volcano-tectonic earthquakes. First, the S -wave quality factor for the investigated area was experimentally calculated, and then the distance-correction curve, log A 0 ( r ), to be used in the Richter formula M L =log A max −log A 0 ( r ), was numerically estimated by measuring the attenuation properties and, hence, propagating a synthetic S -wave packet in the earth medium. The local magnitude scale was normalized to fit the Richter formula that was valid for Southern California at a distance of 10 km. M L was estimated by synthesizing Wood–Anderson seismograms and measuring the maximum amplitude. For the same dataset, the moment magnitude was obtained from S -wave distance-corrected and site-corrected displacement spectra. Comparisons between local and moment magnitudes determined, along with the old duration magnitude ( M D ) routinely used at the Istituto Nazionale di Geofisica e Vulcanologia–Osservatorio Vesuviano, are presented and discussed. Moreover, the relationships between M L and M w calculated for two reference sites are also derived.