Surface wave tomography and seismic source studies at Campi Flegrei (Italy).

We analyse a set of events, recorded in March 1984 during a period of intense seismicity of the last bradyseismic crisis, to determine shallow velocity models and seismic source moment tensors in the Campi Flegrei region. The velocity models of the crust are obtained by surface wave tomography. Two inland negative anomalies of group velocity resulting in our tomographic maps well agree with previous independent measurements whereas a third anomaly, located in the Pozzuoli Gulf and not evidenced by previous studies, is in correspondence with the caldera position. The inversion of the dispersion curves allows us to extend the already available velocity models within the uppermost 2 km of the crust. The obtained models are employed to study seismic source features by the moment tensor analysis. Preliminary synthetic tests are performed in order to minimise artefacts in the moment tensor solutions possibly due to numerical noise, to station distribution or to the structural modelling approximation. Most of the investigated earthquakes are deviatoric mechanisms and the increase of the isotropic component is observed in connection with the change of the seismicity rate in the investigated temporal window