GNGTS 2014 - Atti del 33° Convegno Nazionale

82 GNGTS 2014 S essione 1.1 by means of the standard HYPO71 algorithm (Lee and Lahr, 1975), using the 1D velocity model reported in Milano et al. (2005). This velocity model has been repeatedly utilized to locate the seismicity occurred in the Matese Massif and surrounding in the last 20 years (e.g. the 1997-98 seismic sequence). Re-picking the seismic events also led to obtain a P-wave polarity dataset, that has been used to compute focal mechanisms by means of the standard FPFIT grid- search algorithm (Reasenberg and Opphenheimer, 1985). The number of polarity data used (≥ 14) and the fairly good azimuthal coverage of the seismic stations at short epicentral distance (< 80 km) led to stable solutions, with average errors on the maximum likelihood solutions < 10 degree for strike, dip and rake. The epicentral distribution of about 260 best located events of the sequence, whose magnitude is 1.8 ≤ M L ≤ 4.9, is shown in Fig. 2 (top, left panel). Maximum error location on horizontal position and depth is 1.5 for both; maximum rms value is 0.45 s. Maximum gap is < 100° ����� ��� ��� � (<50° for the M L > 2.5 events)� ���������� �� ������������ �� �� ���� �� ����� ���� �� . Seismicity is concentrated in an area of about 10x4 km and t�� ���������� ������������ ������� �� ����� �� �� ����� ����� �������� ��������� ����� �� he epicentral distribution depicts an about 10 km long, NW-SE trending alignment ����� �� (Fig. 2, top) ������ ��� ������������� ���� �� ��� ������ ������� ������� ��� �������� �� ��� ����� ����� within the south-eastern part of the Matese ������� ������� ��� �������� �� ��� ����� ����� Massif. Whereas the location of the first main- shock (M L = 4.9) falls in the middle of the sequence alignment, the second main-shock (M L = 4.2) is shifted about 2 km to the SE relative to the first one (red dots in Fig. 2 top, left panel). About 15 km divide t�� ���������� ���� �� ���� �������� ���� ��� ���������� ���� �� ��� ������� he epicentral area of this sequence from the epicentral area of the 1997-98 sequence (Fig. 1). Fig. 2 – Top, left: Epicentral distribution of the 2013-14 sequence. The size of the circles is proportional to the magnitude of the events. Red dots represent the M L = 4.9 and the M L = 4.2 main-shocks. Top, right: Fault plane solutions of the events with magnitude greater than 2.8 and their location. Bottom: Hypocentral distribution of the events of the 2013-14 sequence (red circles) and of the events of the 1997-98 sequence (blue circles) along the NW-SE (B-B’) and SW-NE (A-A’) directions. The size of the circles is proportional to the magnitude of the events.