Seismic moment tensor resolution by waveform inversion of a few local noisy records .2. Application to the Phlegraean Fields (Southern Italy) volcanic tremors

Seismic sources with non-double-couple (non-DC) components are frequently observed in volcanic and geothermal areas. This suggests that the non-DC components may be generated by phenomena such as movements of magmatic fluids under high pressure and intrusions of dykes, which characterize volcanic areas and are believed to be responsible for volcanic tremors. Several volcanic tremors from the Phlegraen Fields, Southern Italy, have been processed with the waveform Inversion method, which allows us to estimate the error on the source mechanism and on the source time function due to the noise present in the seismograms, the hypocentre mislocation and, in a simplistic way, an improper structure modelling. The events treated are examples of the seismicity accompanying the upward bradyseism of the area in 1984, and the following downward bradyseism is 1986. Significant non-DC components, i.e. a volumetric part and a compensated linear vector dipole (CLVD), are found in the mechanism, which indicates movement of magmatic fluids in the area.