The Italian guidelines for seismic risk classification of constructions: technical principles and validation

The Italian “Guidelines for the seismic risk classification of constructions” approved in February 2017 define the technical principles for exploiting tax deductions with respect to seismic strengthening interventions on existing buildings (Sismabonus). Tax deductions represent a unique opportunity to improve the seismic safety of the existing Italian building stock. The guidelines are very simple and allow practitioners to deal with the sophisticated concepts behind modern seismic design, such as expected annual losses (EAL) and repair costs (expressed as a fraction of the Reconstruction Cost: %RC). The seismic risk classes of buildings and the class upgrade due to strengthening interventions can be assessed using the principles included in the guidelines. The seismic risk class is the minimum between the class defined by the building safety index at the ultimate limit state and the one related to the EAL. The latter class depends on the area under the curve of the expected losses, which is easily obtained by computing the safety index converted in the return period (annual frequency) at different limit states and the relevant %RC. This paper illustrates the technical principles at the base of the guidelines and the procedure used to calibrate the repair costs associated with the different limit states using the actual repair costs monitored in the reconstruction process following recent Italian earthquakes. Finally, simple tools to estimate the cost of the strengthening interventions to improve the seismic capacity at the life-safety limit states are provided.     

Geologic remote sensing (Ninth Thematic Conference)

Geologic remote sensing (Ninth Thematic Conference)     

The interannual variability of the surface eddy kinetic energy in the Labrador Sea

The variability of the surface eddy kinetic energy (EKE) in the Labrador Sea is investigated with a suite of numerical integrations using a regional ocean model. Simulations are performed over the period 1980–2001 and are compared to satellite observations over the last 9 years. The surface EKE pattern in the basin is dominated by a region along the West coast of Greenland where eddies, mainly anticyclonic, are formed by instability of the main currents flowing over the continental slope, consistent with previous idealized results. Here the interannual changes are linked to the shear of the incoming boundary current system imposed as boundary condition to the model domain. The highly variable strength of the East Greenland current at the northeast boundary, derived from the Simple Ocean Data Assimilation (SODA) reanalysis, strongly influences the vortex formation.In the center of the Labrador Sea, where deep convection occurs, a statistically significant portion of the modeled interannual surface EKE variability is correlated with the local atmospheric forcing, and both heat and wind fluxes play an important role and can be adopted as predictors at a lag of 2–3 months. The Arctic Oscillation index can also be used as a remote indicator of the atmospheric fluxes, but with lower skill than local measurements. In contrast the North Atlantic Oscillation index does not correlate significantly with the surface EKE at intraseasonal and interannual scales. The analysis of altimeter data over the 1993–2001 supports the existence of this asymmetry between the regime locally forced by the atmosphere in the central basin, and the regime remotely forced by the incoming boundary current along the west Greenland coast. Those results have important implications for monitoring and predicting the surface eddy kinetic energy variability in the Labrador Sea.     

Seismic structure and tectonics of the Shackleton Fracture Zone (Drake Passage,Scotia Sea)

The structural framework of the southern part of the Shackleton Fracture Zone has been investigated through the analysis of a 130-km-long multichannel seismic reflection profile acquired orthogonally to the fracture zone near 60° S. The Shackleton Fracture Zone is a 800-km-long, mostly rectilinear and pronounced bathymetric lineation joining the westernmost South Scotia Ridge to southern South America south of Cape Horn, separating the western Scotia Sea plate from the Antarctic plate. Conventional processing applied to the seismic data outlines the main structures of the Shackleton Fracture Zone, but only the use of enhanced techniques, such as accurate velocity analyses and pre-stack depth migration, provides a good definition of the acoustic basement and the architecture of the sedimentary sequences. In particular, a strong and mostly continuous reflector found at about 8.0 s two-way traveltime is very clear across the entire section and is interpreted as the Moho discontinuity. Data show a complex system of troughs developed along the eastern flank of the crustal ridge, containing tilted and rotated blocks, and the presence of a prominent listric normal fault developed within the oceanic crust. Positive flower structures developed within the oceanic basement indicate strike-slip tectonism and partial reactivation of pre-existing faults. Present-day tectonic activity is found mostly in correspondence to the relief, whereas fault-induced deformation is negligible across the entire trough system. This indicates that the E–W-directed stress regime present in the Drake Passage region is mainly dissipated along a narrow zone within the Shackleton Ridge axis. A reappraisal of all available magnetic anomaly identifications in the western Scotia Sea and in the former Phoenix plate, in conjunction with new magnetic profiles acquired to the east of the Shackleton Fracture Zone off the Tierra del Fuego continental margin, has allowed us to propose a simple reconstruction of Shackleton Fracture Zone development in the general context of the Drake Passage opening.     

The imprint of the equation of state on the axial w-modes of oscillating neutron stars

We discuss the dependence of the pulsation frequencies of the axial quasi-normal modes of a non-rotating neutron star upon the equation of state describing the star interior. The continued fraction method has been used to compute the complex frequencies for a set of equations of state based on different physical assumptions and spanning a wide range of stiffness. The numerical results show that axial gravitational waves carry relevant information on both the structure of neutron star matter and the nature of the hadronic interactions.     

Land use changes,torrent control works and sediment mining: effects on channel morphology and sediment flux,case study of the Reno River (Northern Italy)

As with most Italian rivers, the Reno River has a long history of human modification, related also to morphological changes of the lower Po River since Roman times, but in the last decades, significant land use changes in the headwaters, dam construction, torrent control works and extensive bed material mining have caused important channel morphology and sediment budget changes. In this paper, two main types of channel adjustment, riverbed incision and channel narrowing, are analysed. Riverbed degradation is discussed by comparing four different longitudinal profiles surveyed in 1928, 1951, 1970 and 1998 in the 120 km long reach upstream of the outlet. The analysis of channel narrowing is carried out by comparing a number of cross‐sections surveyed in different years across the same downstream reach. Field sediment transport measurements of seven major floods that occurred between 2003 and 2006 are compared with the bedload transport rates predicted by the most renowned equations. The current low bedload yield is discussed in terms of sediment supply limited conditions due to land use changes, erosion‐control works and extensive and out of control bed material mining that have affected the Reno during the last decades. Copyright © 2011 John Wiley & Sons, Ltd.     

Displacement prediction of step-like landslide by applying a novel kernel extreme learning machine method

Landslide displacement prediction is an essential component for developing landslide early warning systems. In the Three Gorges Reservoir area (TGRA), landslides experience step-like deformations (i.e., periods of stability interrupted by abrupt accelerations) generally from April to September due to the influence of precipitation and reservoir scheduled level variations. With respect to many traditional machine learning techniques, two issues exist relative to displacement prediction, namely the random fluctuation of prediction results and inaccurate prediction when step-like deformations take place. In this study, a novel and original prediction method was proposed by combining the wavelet transform (WT) and particle swarm optimization-kernel extreme learning machine (PSO-KELM) methods, and by considering the landslide causal factors. A typical landslide with a step-like behavior, the Baishuihe landslide in TGRA, was taken as a case study. The cumulated total displacement was decomposed into trend displacement, periodic displacement (controlled by internal geological conditions and external triggering factors respectively), and noise. The displacement items were predicted separately by multi-factor PSO-KELM considering various causal factors, and the total displacement was obtained by summing them up. An accurate prediction was achieved by the proposed method, including the step-like deformation period. The performance of the proposed method was compared with that of the multi-factor extreme learning machine (ELM), support vector regression (SVR), backward propagation neural network (BPNN), and single-factor PSO-KELM. Results show that the PSO-KELM outperforms the other models, and the prediction accuracy can be improved by considering causal factors.     

The origins of Antarctic rock glaciers: periglacial or glacial features?

In extensively glaciarized permafrost areas such as Northern Victoria Land, rock glaciers are quite common and are considered postglacial cryotic landforms. This paper reveals that two rock glaciers in Northern Victoria Land (at Adélie Cove and Strandline) that are located close to the Italian Antarctic Station (Mario Zucchelli Station) should have the same origin, although they were previously mapped as Holocene periglacial landforms and subsequently considered ice‐cored and ice‐cemented rock glaciers, respectively. In fact, by integrating different geophysical investigations and borehole stratigraphy, we show that both landforms have similar internal structures and cores of buried glacier ice. Therefore, this kind of rock glacier is possibly related to the long‐term creep of buried ice rather than to permafrost creep alone. This interpretation can be extended to the larger part of the features mapped as rock glaciers in Antarctica. In addition, a high‐reflective horizon sub‐parallel to the topographic surface was detected in Ground Probing Radar (GPR) data over a large part of the study area. Combining all the available information, we conclude that it cannot be straightforwardly interpreted as the base of the active layer but rather represents the top of a cryo‐lithological unit characterized by ice lenses within sediments that could be interpreted as the transition zone between the active layer and the long‐term permafrost table. More generally, knowledge of the subsurface ice content and, in particular, the occurrence of massive ice and its depth is crucial to make realistic and affordable forecasts regarding thermokarst development and related feedbacks involving GHG emissions, especially in the case of cryosoils rich in carbon content. Copyright © 2017 John Wiley & Sons, Ltd.     

Linkages between the North Pacific Oscillation and central tropical Pacific SSTs at low frequencies

The North Pacific Oscillation (NPO) recently (re-)emerged in the literature as a key atmospheric mode in Northern Hemisphere climate variability, especially in the Pacific sector. Defined as a dipole of sea level pressure (SLP) between, roughly, Alaska and Hawaii, the NPO is connected with downstream weather conditions over North America, serves as the atmospheric forcing pattern of the North Pacific Gyre Oscillation (NPGO), and is a potential mechanism linking extratropical atmospheric variability to El Ni?o events in the tropical Pacific. This paper explores further the forcing dynamics of the NPO and, in particular, that of its individual poles. Using observational data and experiments with a simple atmospheric general circulation model (AGCM), we illustrate that the southern pole of the NPO (i.e., the one near Hawaii) contains significant power at low frequencies (7–10?years), while the northern pole (i.e., the one near Alaska) has no dominant frequencies. When examining the low-frequency content of the NPO and its poles separately, we discover that low-frequency variations (periods >7?years) of the NPO (particularly its subtropical node) are intimately tied to variability in central equatorial Pacific sea surface temperatures (SSTs) associated with the El Ni?o-Modoki/Central Pacific Warming (CPW) phenomenon. This result suggests that fluctuations in subtropical North Pacific SLP are important to monitor for Pacific low-frequency climate change. Using the simple AGCM, we also illustrate that variability in central tropical Pacific SSTs drives a significant fraction of variability of the southern node of the NPO. Taken together, the results highlight important links between secondary modes (i.e., CPW-NPO-NPGO) in Pacific decadal variability, akin to already established relationships between the primary modes of Pacific climate variability (i.e., canonical El Ni?o, the Aleutian Low, and the Pacific Decadal Oscillation).