Comet Hale—Bopp Shells Expansion: A CCD Study

Using a CCD camera attached to the 0.335 m and 0.20 m reflectors of S.A.S. Observatory (Novara, Italy), we followed the linear jets and shells of comet Hale–Bopp between May 1996 and May 1997. In addition to confirming the model of Sekanina and Bohenhardt (1997), the study of the linear jets provided indications concerning the orientation of the comet's axis of rotation over time. The study of the shells revealed that the speed at which they move away from the nucleus was not constant. A periodic variation of the shell expansion velocity may not be excluded : if so, a possible precessional effect on the axis of rotation of the comet's nucleus could explain this behavior. This revised version was published online in July 2006 with corrections to the Cover Date.     

Slope Stabilisation by Perennial “Gramineae” in Southern Italy: Plant Growth and Temporal Performance

In the territory of Altomonte, a village located in Calabria, in the Southern part of Italy, a new thermoelectrical station is under construction. This work involved major earthworks which regarded new excavated slopes. In order to protect soil from erosion due to rainfall and runoff and also in order to prevent superficial soil instability, it was decided to plant four different species of perennial “gramineae” plants (Eragrass, Elygrass, Pangrass and Vetiver) characterised by deep roots. Works began in November 2002 and ended in May 2003, a period marked by very different climate and meteorological conditions, varying from exceptionally rainy and cold winter to warm and dry spring months. The paper describes the different stages of the project and the monitoring programme for the following months. The extension of the work and the use of four different kinds of vegetation made periodic inspections of the entire site appropriate. Two in situ investigations, respectively performed in August 2003 and in November 2003, are outlined. The aim of these surveys was to confirm the success of the work by verifying the growth of the plants and roots. The principal monitored parameters were the percentage of sprouted plants, the height of the foliage and the depth of roots. The investigations showed good results, keeping in mind the very difficult climatic conditions and the extreme poor fertility of the topsoil laid down upon the clay layer: in particular, high survival rate were measured over the entire area of the works and the root systems have developed sufficiently to grow through the upper topsoil layer (0.2–0.3 m) into the underlying clay layer. In March 2004, a sampling programme was undertaken on the same site. Direct shear tests were carried out in the laboratory in order to evaluate the increase in shear strength of the rooted soil mass. The research involved the recovery of three undisturbed samples of soil with roots for each of the four types of “gramineae” plants and three undisturbed samples constituted only of soil, from the surface to a depth of 1.0 m. The tests were performed in a large direct shear apparatus on 200 mm diameter samples. The test results allowed to evaluate the roots’ contribution of the different gramineous species and to underline the direct correlation between the increase in soil shear strength and the root tensile strengths. In particular, an increase in cohesion ranging between 2 kPa and 15 kPa was recorded, according to the different species: the maximum values of increase in shear strength were reached by Vetiver roots, which are also characterised by the highest tensile strength.     

Semi-automated regional classification of the style of activity of slow rock-slope deformations using PS InSAR and SqueeSAR velocity data

Large slow rock-slope deformations, including deep-seated gravitational slope deformations and large landslides, are widespread in alpine environments. They develop over thousands of years by progressive failure, resulting in slow movements that impact infrastructures and can eventually evolve into catastrophic rockslides. A robust characterization of their style of activity is thus required in a risk management perspective. We combine an original inventory of slow rock-slope deformations with different PS-InSAR and SqueeSAR datasets to develop a novel, semi-automated approach to characterize and classify 208 slow rock-slope deformations in Lombardia (Italian Central Alps) based on their displacement rate, kinematics, heterogeneity and morphometric expression. Through a peak analysis of displacement rate distributions, we characterize the segmentation of mapped landslides and highlight the occurrence of nested sectors with differential activity and displacement rates. Combining 2D decomposition of InSAR velocity vectors and machine learning classification, we develop an automatic approach to characterize the kinematics of each landslide. Then, we sequentially combine principal component and K-medoids cluster analyses to identify groups of slow rock-slope deformations with consistent styles of activity. Our methodology is readily applicable to different landslide datasets and provides an objective and cost-effective support to land planning and the prioritization of local-scale studies aimed at granting safety and infrastructure integrity.

     

The SISMA prototype system: integrating Geophysical Modeling and Earth Observation for time-dependent seismic hazard assessment

An innovative approach to seismic hazard assessment is illustrated that, based on the available knowledge of the physical properties of the Earth structure and of seismic sources, on geodetic observations, as well as on the geophysical forward modeling, allows for a time-dependent definition of the seismic input. According to the proposed approach, a fully formalized system integrating Earth Observation data and new advanced methods in seismological and geophysical data analysis is currently under development in the framework of the Pilot Project SISMA, funded by the Italian Space Agency. The synergic use of geodetic Earth Observation data (EO) and Geophysical Forward Modeling deformation maps at the national scale complements the space- and time-dependent information provided by real-time monitoring of seismic flow (performed by means of the earthquake prediction algorithms CN and M8S) and permits the identification and routine updating of alerted areas. At the local spatial scale (tens of km) of the seismogenic nodes identified by pattern-recognition analysis, both GNSS (Global Navigation Satellite System) and SAR (Synthetic Aperture Radar) techniques, coupled with expressly developed models for interseismic phase, allow us to retrieve the deformation style and stress evolution within the seismogenic areas. The displacement fields obtained from EO data provide the input for the geophysical modeling, which eventually permits to indicate whether a specific fault is in a “critical state.” The scenarios of expected ground motion (shakemaps) associated with the alerted areas are then defined by means of full waveforms modeling, based on the possibility to compute synthetic seismograms by the modal summation technique (neo-deterministic hazard assessment). In this way, a set of deterministic scenarios of ground motion, which refer to the time interval when a strong event is likely to occur within the alerted area, can be defined both at national and at local scale. The considered integrated approach opens new routes in understanding the dynamics of fault zones as well as in modeling the expected ground motion. The SISMA system, in fact, provides tools for establishing warning criteria based on deterministic and rigorous forward geophysical models and hence allows for a well-controlled real-time prospective testing and validation of the proposed methodology over the Italian territory. The proposed approach complements the traditional probabilistic approach for seismic hazard estimates, since it supplies routinely updated information useful in assigning priorities for timely mitigation actions and hence it is particularly relevant to Civil Defense purposes.     

Comet McNaught (260P/2012 K2): spin axis orientation and rotation period

Extensive observations of comet 260P/McNaught were carried out between August 2012 and January 2013. The images obtained were used to analyze the comet’s inner coma morphology at resolutions ranging from 250 to about 1000 km/pixel. A deep investigation of the dust features in the inner coma allowed us to identify only a single main active source on the comet’s nucleus, at an estimated latitude of ?50^°±15^°. A thorough analysis of the appearance and of the motion of the morphological structures, supported by graphic simulations of the geometrical conditions of the observations, allowed us to determine a pole orientation located within a circular spot of a 15^°-radius centered at RA=60^°, Dec=0^°. The rotation of the nucleus seems to occur on a single axis and is not chaotic, furthermore no precession effects could be estimated from our measurements. The comet’s spin axis never reached the plane of the sky from October 2012 to January 2013; during this period it did not change its direction significantly (less than 30^°), thus giving us the opportunity to observe mainly structures such as bow-shaped jets departing from the single active source located on the comet’s nucleus. Only during the months of August 2012 and January 2013 the polar axis was directed towards the Earth at an angle of about 45^° from the plane of the sky; this made it possible to observe the development of faint structures like fragments of shells or spirals. A possible rotation period of 0.340±0.01 days was estimated by means of differential photometric analysis.     

Comet Machholz (C/2004 Q2): morphological structures in the inner coma and rotation parameters

Extensive observations of comet C/2004 Q2 (Machholz) were carried out between August 2004 and May 2005. The images obtained were used to investigate the comet’s inner coma features at resolutions between 350 and 1500 km/pixel.