Cianfarra, Paola

This study presents the interpretation of radio echo-sounding (RES) data collected during the 2003 geophysical campaign of PNRA (Italian National Research Project in Antarctica), which focused on the exploration of the Concordia Trench-Lake system in East Antarctica. The data allow us to identify a new lake (ITL-28) at the southern edge of the Concordia Trench and a series of N–S trending subglacial troughs cutting through the Belgica Highlands. We have mapped the bedrock morphology at 3 km resolution, which led to an improved geographical and geomorphological characterization of the Concordia Trench, Concordia Ridge, Concordia Lake and South Hills. Improved knowledge of the Concordia Trench allowed us to model the 3-D geometry of the Concordia fault, suggesting that it played a role in governing the morpho-tectonic evolution of the bedrock in the Dome C region, and to propose a Cenozoic age for its activity. We recognize the importance of catchment basin morphology in hosting subglacial lakes, and discuss the role played by tectonics, glacial scouring and volcanism in the origin of the trench lakes, basin lakes and relief lakes, respectively.

Abstract A semi-permanent Global Positioning System (GPS) network of about 30 vertices: Victoria Land Network for DEFormation control (VLNDEF) has been set up since Austral summer 1998 at Terra Nova Bay (TNB) near Ross Sea in Antarctica. A permanent GPS station TNB1 based on dual frequency Ashtech P-code GPS receiver with a Choke Ring Antenna has been installed on a bedrock monument in October 1998 and has recorded continuously until recently. The GPS network has been routinely surveyed every two summers using high quality dual frequency GPS receivers; data, metadata and solutions are available to the scientific community at (http://www.geodant.unimore.it). Results of a distributed session approach applied to process GPS data of the VLNDEF network are presented in this paper, based on Gamit/Globk 10.35 GPS analysis software. An improved reference frame definition was implemented using Globk package in order to compute Antarctic intra-plate residual velocities and to invert the strain field from GPS data in this region. The strain rate obtained from the inversion of VLNDEF GPS data has been computed following the method proposed by Feigl et al. using QOCA (quasi observation combination analysis) 1.34 GPS data analysis package.

The technique of the wavefield polarization is applied to ambient vibrations recorded in the Mefite d’Ansanto area, an important non-volcanic natural emission of low temperature CO2 enriched gases. Twentyfive measurements were performed in the study area, eleven near the emission site and the other fourteen in different sites within an area of 5 km. Polarization is assessed both in the frequency and time domain through the individual-station horizontal-to-vertical spectral ratio and covariance-matrix analysis, respectively. We find a significant tendency of ground motion in the gas emission area to be polarized in the horizontal plane, with a N115 predominant trend. This polarization tends to disappear while moving far from the site. According to previous papers in other study areas, such a directional effect is likely caused by fault-induced fractures and tends to be orthogonal to the fracture strike. The predominant NW–SE regional faulting does not fit the N115 polarization direction. To explain observations, we propose an interpretation in terms of a NE–SW oriented, local transfer fault as inferred from the lineament analysis. The intersection of the damage zone of this fault with the regional NW–SE normal fault system could easily be the responsible for the gas emissions since it favors a locally increased crustal weakness.

A semi-permanent global positioning system (GPS) network of 30 vertices known as the Victoria Land Network for Deformation Control (VLNDEF) was set-up in the Austral summer of 1998 in Northern Victoria Land (NVL), including Terra Nova Bay (TNB), Antarctica. The locations were selected according to the known Cenozoic fault framework that is characterized by a system of NW-SE regional faults with right-lateral, strike-slip kinematics. The TNB1 permanent GPS station is within the VLNDEF, and following its installation on a bedrock monument in October 1998 it has been recording almost continuously. The GPS network has been surveyed routinely every two summers, using high-quality, dual-frequency GPS receivers. In this study, we present the results of a distributed session approach applied to the processing of the GPS data of the VLNDEF. An improved reference frame definition was implemented, including a new Euler pole, to compute the Antarctic intra-plate residual velocities. The projection of the residual velocities on the main faults in NVL show present-day activities for some faults, including the Tucker, Leap Year, Lanterman, Aviator, and David faults, with rightlateral strike-slip kinematics and local extensional/ compressional components. This active fault pattern divides NVL into eight rigid blocks, each characterized by their relative movements and rigid rotations. These show velocities of up to several mm/yr, which are comparable to those predicted by plate tectonic theory at active plate margins.

A Global Positioning System (GPS) network of 30 semi-permanent vertices known as the Victoria Land Network for Deformation Control (VLNDEF) was set up in the Austral summer of 1998 in Northern Victoria Land (NVL), including the permanent GPS station of Terra Nova Bay (TNB1), Antarctica. The locations were selected according to the known Cenozoic fault framework, which is characterized by a system of NW[U+2010]SE regional faults with right[U+2010]lateral, strike[U+2010]slip kinematics. The TNB1 permanent GPS station is included within the VLNDEF, and was installed on a bedrock monument in October 1998, it has been recording almost continuously up to the present. The GPS network has been surveyed routinely every two summers, using high[U+2010]quality, dual[U+2010]frequency GPS receivers like Trimble 5700, TopCon GB100, and Ashtech Z-XII. In this study we present the results of a distributed session approach based on Gamit/Globk 10.4 software package applied to the processing of the GPS data of the VLNDEF aimed to obtain the preliminary framework of the active tectonics of this region of Antarctica. An improved reference frame definition was implemented, including a new Euler rotation pole, to compute the Antarctic intra-plate residual velocities. The projection of the residual velocities on the main faults in NVL show present[U+2010]day activities for some faults, including the Tucker, Leap Year, Lanterman, Aviator, and David faults, with right[U+2010]lateral strike[U+2010]slip kinematics and local extensional and compressional components. This active fault pattern divides NVL into eight rigid blocks, each characterized by its relative movements and rigid rotations. These show velocities of up to several millimeters per year, which are comparable to those predicted by plate tectonic theory at active plate margins. During the austral summer 2010, in the framework of the Italian Antarctic campaign, field investigations at 25 geodetic stations were performed both for survey of the instruments and measurements as well as for the geological study necessary to evaluate the geological stability of the sites. Preliminary analysis of the collected structural data showed the stability of most of the investigated stations, thus confirming the proposed active tectonic framework of the NVL at the regional scale.

Directional amplifications of horizontal ground motion along site-dependent azimuths are often unexpectedly found in rocky environments and in stiff-rock conditions. Directional amplification has been studied by several authors at sites with fractured rocks across fault damage zones (e.g. Pischiutta et al., 2013), or close to gravitational instabilities (e.g. Burjanek et al, 2012). In the majority of the cases, a transversal relation between the maximum amplification and the orientation of the predominant fracture field is recognized, interpreted as the effect of the stiffness anisotropy. Cracks in fault damage zones also cause the reduction of rock velocity (especially near-surface Vs). Studies performed on high number of rocky sites revealed that directional amplification effects are much more diffuse than expected. A systematic study involving 258 seismological stations of the Italian Seismic Network points out that 56 of stations (20%) are clearly affected by directional site amplification effects. This station sample was studied by analyzing the surface topography in order to unravel the role of topographic irregularities on ground motion amplifications. Models proposed in literature predict amplification at wavelengths comparable to the mountain width (e.g. Géli et al, 1988) and the scatter of wavefield that is polarized in the direction orthogonal to the relief elongation (e.g. Spudich et al., 1996). Since some bias exists in the objective quantification morphological parameters, we use an original methodology that combines morphometric analysis of digital elevation models and principal component analysis to define the dimension and elongation orientation of pronounced ridges. This study showed that the expected relations between the shape/dimension of relief and ground motion were found only at 5 stations (out of 56) , suggesting a major of local morphology, geological complexities and subsurface properties on directional amplification, consistently with Burjanek et al. (2014). Thus, recent findings have suggested that models proposed in literature in many cases are not able to reproduce observations even for damaging earthquakes (Avallone et al., 2014). Much effort has to be devoted in the future to model the amplification mechanism and take it into account in seismic hazard assessment

In Antarctica, the severe climatic conditions and the thick ice sheet that covers the largest and most internal part of the continent make it particularly difficult to systematically carry out geophysical and geodetic observations on a continental scale. It prevents the comprehensive understanding of both the onshore and offshore geology as well as the relationship between the inner part of East Antarctica (EA) and the coastal sector of Victoria Land (VL). With the aim to reduce this gap, in this paper multiple geophysical dataset collected since the 1980s in Antarctica by Programma Nazionale di Ricerche in Antartide (PNRA) were integrated with geodetic observations. In particular, the analyzed data includes: (i) Geodetic time series from Trans Antarctic Mountains DEFormation (TAMDEF), and Victoria Land Network for DEFormation control (VLNDEF) GNSS stations installed in Victoria Land; (ii) the integration of on-shore (ground points data and airborne) gravity measurements in Victoria Land and marine gravity surveys performed in the Ross Sea and the narrow strip of Southern Ocean facing the coasts of northern Victoria Land. Gravity data modelling has improved the knowledge of the Moho depth of VL and surrounding the offshore areas. By the integration of geodetic and gravitational (or gravity) potential results it was possible to better constrain/identify four geodynamic blocks characterized by homogeneous geophysical signature: the Southern Ocean to the N, the Ross Sea to the E, the Wilkes Basin to the W, and VL in between. The last block is characterized by a small but significant clockwise rotation relative to East Antarctica. The presence of a N-S to NNW-SSE 1-km step in the Moho in correspondence of the Rennick Geodynamic Belt confirms the existence of this crustal scale discontinuity, possibly representing the tectonic boundary between East Antarctica and the northern part of VL block, as previously proposed by some geological studies.

Directional site effects observed at seismological stations on pronounced relief are analysed. We investigate the ground motion properties calculating horizontal-to-vertical spectral ratios and horizontal polarization of both ambient vibrations and earthquake records using broad- band seismograms of the Italian seismic network. We find that a subset of 47 stations with pronounced relief results in a significant (>2) directional amplification of the horizontal component, with a well-defined, site-specific direction of motion. However, the horizontal spectral response of sites is not uniform, varying from an isolated (resonant) frequency peak to a broad-band amplification, interesting frequency bands as large as 1–10 Hz in many cases. Using 47 selected stations, we have tried to establish a relation between directional amplification and topography geometry in a 2-D vision, when applicable, through a morphological analysis of the digital elevation model using geographic information systems. The procedure computes the parameters that characterize the geometry of topographic irregularities (size and slope), in combination with a principal component analysis that automatically yields the orientation of the elongated ridges. In seeking a relation between directional amplification and the surface morphology, we have found that it is impossible to fit the variety of observations with a resonant topography model as well as to identify common features in the ground motion behaviour for stations with similar topography typologies. We conclude that, rather than the shape of the topography, local structural complexities and details of the near-surface structure must play a predominant role in controlling ground motion properties at sites with pronounced relief.

We present the interpretation of 11 radio echo-sounding (RES) missions carried out over the Vostok–Dome Concordia region during the Italian Antarctic expeditions in the period 1995– 2001. The extension and the density of the radar data in the surveyed area allowed to reconstruct a reliable subglacial morphology and to identify four relevant morphological structures namely: the Aurora trench, the Concordia trench, the Concordia ridge and the South Hills. These structures show evidence compatible with the presence of tectonic features. Morphological considerations indicate their development in Cenozoic time. Hybrid cellular automata (HCA)- based numerical modelling allowed to justify a possible role played by the tectonics of the Aurora and Concordia trench evolution. This was accomplished by matching the bed profiles along opportunely projected sections with the modelled surfaces as derived by the activity of normal faults with variable surfaces within the continental crust. The Vostok–Dome C region is characterized by a large number of subglacial lakes. From the analysis of basal reflected power echo, we identified 14 new lakes and obtained information about their physiography as well as their possible relations with tectonics.We propose a grouping of subglacial lakes on the base of their physiography and geological setting, namely relief lakes, basin lakes and trench lakes. Relief lakes located in the Belgica subglacial highlands and are characterized by sharp and steep symmetric edges, suggesting a maximum water depth of the order of 100 m. Their origin may well relate to localized, positive geothermal flux anomalies. Basin lakes located in the Vincennes subglacial basin and are characterized by wider dimension that allow the development of well-defined, flat ice surface anomalies. Trench lakes characterize the Aurora and Concordia trenches as the possible effect of normal fault activity. Key words: Antarctica, HCA modelling, radio echo sounding, subglacial