GNGTS 2016 - Atti del 35° Convegno Nazionale

GNGTS 2016 S essione 1.3 267 and filtered waveforms helped in the estimation of S wave polarity. However, many events remained undetermined due to the insufficient coverage of the focal sphere with the available observed phase polarity. We were able to compute the focal mechanism for 36 VT earthquakes recorded from 2005 to 2015 (Fig. 1). For at least 30 of them the solution is well constrained, with uncertainty of less than 10 degrees on the estimated strike, dip, and rake. Only for few events the solution is affected by uncertainty up to 30 degrees on one or more of the three angles. Of course this happens for the events characterized by poor data quality, those of lower magnitude and/or those recorded by less than 10 stations. The increased number of stations after 2008 allowed for a better location of the source and a much better coverage of the focal sphere, thus permitting a reliable estimation of the focal mechanisms. Earthquakes occurred after 2010 in the central area of the caldera are located with gap smaller than 90 degrees, and the estimation of focal mechanisms has become feasible and reliable for any event of M>1, but in particularly favorable cases we were able to find a good solution even for events as small as M0.5. Among the 36 computed mechanisms two thirds (24) are classifiable as normal faults (red in Fig. 1), while the reverse solutions are only 2 (magenta in Fig. 1). Solutions with nearly vertical fault (dip slip and strike slip mechanisms) counts 10 earthquakes (orange in Fig. 1). Fig. 2 shows the values of the three angles found for all focal mechanisms shown in Fig. 1. Their distribution is quite homogeneous with regard to strike, while solutions with dip smaller Fig. 1 – ��� �� ����� ������� ������� ������� ��� ������� �� ����� Map of Campi Flegrei caldera showing the results of focal mechanisms analysis. Blue symbols represent the seismic stations used in this analysis and/or currently installed. The size of beach ball is proportional to magnitude (0.6 <– M <– 2.5). Fig. 2 – ��� ����� ��� ���� ������ ������ ������ ������ �� ��� ����� ���������� ����� �� ���� �� Dip (red) and rake (blue) angles versus strike of the focal mechanisms shown in Fig. 1.