GNGTS 2016 - Atti del 35° Convegno Nazionale

GNGTS 2016 S essione 1.1 127 A seismotectonic picture of the Argentera-Mercatour massif E. Eva 1 , M.G. Malusà 2 , S. Solarino 1 1 Ist. Naz. Geofisica e Vulcanologia, Genova, Italy 2 Università Bicocca, Milano, Italy T�� ���������� �� ��� ������������ ������� ���� ����� ��� �� �������� ��������� he seismicity of the southernmost western Alps shows low to moderate magnitude (3 < M L < 5). In that segment of the Alpine orogen, ����� ���������� ���������� ��� �������� major earthquake occurrence �������� and greatest seismic hazard characterize the transition zone between the Maritime Alps and the Ligurian- Provençal basin (Eva and Solarino, 1998; Baroux et al. , 2001; Larroque et al. , 2009). Despite the seismic potential of this sector of the belt, the active fault network sparking off the regional seismic activity is not yet clearly identified, and is currently under investigation. Ongoing brittle deformation in the southern Western Alps is largely controlled by inherited Alpine faults. These faults include the frontal thrusts developed beneath the External Massifs, and the major strike-slip faults crosscutting the Frontal Pennine Fault (e.g., the Stura Fault; Malusà et al. , 2009). The Stura Fault now juxtaposes the European continental crust that has escaped Alpine metamorphism, to the SW, and Alpine metamorphic units to the NW, and possibly acted as a lateral ramp accomodating post-Oligocene Adria-Europe convergence (Malusà et al. , 2015, and references therein). From a seismotectonic point of view, the Argentera-Mercantour Massif is characterized by a diffuse seismicity that becomes very firm to the north-east in correspondence of the Stura Fault. However, when dealing with seismotectonic studies, the accuracy of routinely located earthquakes is not sufficient to clearly define the active faults. In this study, we analyzed the distribution of seismicity after relocation with the algorithm HypoDD ����������� ��� (Waldhauser and Ellsworth, 2000)� ���� ���� ������ ��� ������� �� ���� ���������� ����� ������� ��� ��������� . This code solves the problem of both inaccurate phase picking and reference model being independent from the initial velocity model. We selected 2900 well locatable earthquakes ��� ��� ������ ��������� �������� ��������� �������� ����� �� ���� �������� for the period 1986-2014 adopting selection criteria based on both location parameters reliability and number of phase (8) picks. The high quality relocated database consists of more than 2600 entries with values less than 1.0 km and 1.5 km for horizontal and vertical errors respectively. Fig. 1 – Distribution of HypoDD relocated seismicity. PFT: Penninic Thrust Front, SF: Stura Fault, ST: Saorge-Taggia fault.