GNGTS 2014 - Atti del 33° Convegno Nazionale

Since the hill morphology is parallel to the fault, polarization is found to be nearly orthogonal to the hill elongation. We stress that the earth surface morphology has a strict relation with fracture zones (areas of more intense, closely spaced fracturing) or other discontinuities (faults, geologic contacts) that undergo differential weathering. In fact, fractured zones are more susceptible to mechanical and chemical weathering than unfractured rocks (Mabee et al. , 1994). This is the common link between tectonics and the earth surface morphology. Conclusions. According to Burjanek et al. (2014b) the main conclusion is that the amplification is controlled in first place by the sub-surface rock properties and cannot be simply ascribed to the topography geometry. Previous papers stress that: 1 The subsurface velocity and structure play a major role. Burjanek et al. (2014a, 2014b) have found that the rock sites (EC8 class A) with pronounced topography did not exhibit any systematic amplification on average whereas the rest of the sites (non EC8 class A) presented systematic frequency dependent amplifications. 2 The observed amplifications are strongly directional. �������� Burjanek et al. (2014b) and Pischiutta et al. ������ �������� ���� � ������� ���� ������� ������������ ��� ���������� (2011) assessed that a general link between polarization and topography elongation has not been identified yet since the expected transversal relation was not recurrently found. 3 Effects are very persistent. Pischiutta et al. (2011) have found that 29% of rock stations Fig. 3 – Ambient noise polarization at four stations installed across the Campo Imperatore normal fault (CAM2, CAM 11, CAM15 and CAM20). At each station the rose diagram (cyan) obtained by the covariance matrix analysis are drawn as well as HVSR contour plots (the amplitude scale is different for each plot). The strike of faults and extensional fractures measured by a detailed geological survey at one location (violet star) are reported as well through violet circular histograms. 258 GNGTS 2014 S essione 2.2