GNGTS 2018 - 37° Convegno Nazionale

GNGTS 2018 S essione 1.1 43 An integrated, multi-constrained and multi-scale picture of the upper crustal structure of the IFZ was obtained by combining geological evidences, lithological properties, accurate DD earthquake locations, high resolved P- and S-wave velocity and attenuation tomographic images and information about rock micro-parameters (Amoroso et al. , 2014; De Landro et al. , 2015; Amoroso et al. , 2017). Data and Methods. Since 2005, the capability of detecting and locating small-magnitude events in this area has been greatly improved (Stabile et al., 2013) with the deployment of the dense, wide dynamic range, Irpinia Seismic Network [ISNet]. Presently, the area exhibits low- magnitude seismicity (M L < 3.5) primarily concentrated in very limited regions along the 1980 Irpinia and 1990-1991 Potenza earthquake fault zones (Fig. 2a) (De Landro et al., 2015). We analysed micro-earthquakes recorded by 42 ISNet and INGV stations with Mw< 3.1, occurred from 08/2005 to 10/2016. We used the manually picked first P- and S-wave arrival times of earthquakes recorded by at least 4 stations. A weighting factor inversely related to the uncertainty on arrival time picking has been assigned and a selection based on the location quality was preliminarily performed. The DD locations were obtained by applying an innovative, non-linear, probabilistic and relative location technique implemented in the NonLinLoc package, that has as main advantages the determination of the probability density function (PDF), the use of differential arrival times as data and the possibility to use a 3D velocity model. The high resolved 3D model was obtained using an iterative and linearized local earthquake tomography. Attenuation model was obtained using the same approach applied to the t* (i.e., the ratio between travel time and attenuation quality factor) measurements obtained by Zollo et al. (2014). The high-resolution and low-smearing model regions are estimated through the analysis of the derivative weight sum, the resolution matrix and checkerboard tests. Fig. 2 - (a) DD earthquake locations of seismicity from 08/2005 to 04/2011, from MRP data (in grey) and from CRP data (in turquoise). Red lines are the surface projection of the 3 faults that ruptured during the 1980 Irpinia earthquake. (b) Comparison of the DD locations with the top of the Apulia Carbonate Platform [modified after Improta et al. (2003)]. (c) Comparison of tomographic cross-sections reported in map a) and the earthquakes. (d) Schematic geological interpretation. The position of interfaces are deduced from both the tomographic model and hypocentre-relocated events. Lithologies and main topographic references are also indicated. The crosses indicate the rough position of the retrieved hypocentres. A dashed line is used to represent the hypothetical “barrier”. Modified after De Landro et al. (2015).