Long-period modelling of MEDNET waveforms for the December 13, 1990 Eastern Sicily earthquake

Abstract

The availability of broad-band digital data allow "the analysis" of the seismic signal in the low-noise frequency band for structural and seismic source studies, We model complete seismograms -surface and body waves - for the December 13, 1 990, Eastern Sicily earthquake, recorded at regional distances on the MEDNET stations AQU, BNI and KEG, The inversion for the moment tensor is carried out following two approaches: a) a model-independent stralegy to fit complete seismograms in the 100-130 s period range; b) the calibration of phase velocity curves along each path to fit surface waves in the 40-100 s range, Both methodologies yield stable and consistent results: the 1990 Eastern Sicily earthquake had a seismic moment of M/o = 37 x 1024 dyne.cm, corresponding lo magnitude values of mb = 5,5, Ms = 5,7, Mw = ML = 5.8. In a second stage, synthetic seismograms arc generated by full reflectivity in the 5-50 s period range, with a new code based on the "minors" integration. By modelling surface waves in the 30-50 s range and body waves to 5 s periods, we derive average velocity models for the Central and Eastern Mediterranean, and constrain the hypocenter of the 1990 Eastern Sicily earthquake to be in the 13-17 km depth range.