Reflections on reflexions – II. Effects of light echoes on the luminosity and spectra of Type Ia supernovae

In this paper, we present and discuss the effects of scattered light echoes (LEs) on the luminosity and spectral appearance of Type Ia supernovae (SNe). After introducing the basic concept of LE spectral synthesis by means of LE models and real observations, we investigate the deviations from pure SN spectra, light and colour curves, the signatures that witness the presence of an LE and the possible inferences on the extinction law. The effects on the photometric parameters and spectral features are also discussed. In particular, for the case of circumstellar dust, LEs are found to introduce an apparent relation between the post-maximum decline rate and the absolute luminosity, which is most likely going to affect the well-known Pskowski–Phillips relation.     

Spectral and fragility evaluations of retrofitted structures through strength reduction and enhanced damping

A retrofit procedure for existing buildings called the "weakening and damping technique" (WED) is presented in this paper. Weakening of structures can limit the maximum response accelerations during severe ground motions, but leads to an increase in the displacements or inter-story drifts. Added damping by using viscous dampers, on the other hand, reduces the inter-story drifts and has no significant effect on total accelerations, when structures behave inelastically. The weakening and damping technique addresses the two main causes for both structural and nonstructural damage in structures. The weakening retrofit is particularly suitable for structures that have overstressed components and weak brittle components. In this paper, the advantages of the WeD are verified by nonlinear dynamic analysis and simplified spectral approach that has been modified to fit structures with additional damping devices. A hospital structure located in the San Femando Valley in California is selected as a case study. The results from both analyses show that the retrofit solution is feasible to reduce both structural acceleration and displacement. A sensitivity analysis is also carried out to evaluate the effectiveness of the retrofitting method using different combinations of performance thresholds in accelerations and displacements through fragility analysis.     

The Cimmerian geopuzzle: new data from South Pamir

Based on its Permian‐Triassic stratigraphic and biotic evolution, we correlate the SE Pamir to the Karakoram terrane, and we consider them equivalent, along with the Central Pamir, to the Qiantang Terrane of Tibet, all of Palaeozoic Gondwanan ancestry. We prove the occurrence of a marked Cimmerian unconformity, documented by lowermost Jurassic deposits suturing intensively faulted and folded Permian and Triassic units, which suggests that the South Pamir collided around the T‐J boundary with the Central Pamir along the Rushan‐Pshart suture. Collision of the Karakoram to the South Pamir happened slightly later along the Wakhan‐Tirich Boundary Zone. Progressive time shifting of deformation can be related to the complex setting of the Cimmerian belt, which was subdivided into minor blocks by incipient oceanic basins, providing strong crustal mobility.     

Tectonic features of the Lipari–Vulcano complex (Aeolian archipelago,Italy) from 10 years (1996–2006) of GPS data

The tectonic deformation of the Lipari–Vulcano complex, one of the most important active volcanic areas of the Mediterranean region, is studied here through the analysis of 10 years (1996–2006) of GPS data from both three permanent and 13 non‐permanent stations. This area can be considered crucial for the understanding of the interaction between the Eurasian and African plates in the Mediterranean area, and, in general, this work emphasizes a methodological approach, already applied in other areas worldwide ( J. Geophys. Res., 1996, 101 , 27 957 ; J. Geodyn., 1999, 27 , 213 ) where geodetic data and strain parameters maps of critical areas can help to improve our understanding of their geodynamical aspects. In this framework, this study is aimed at providing a kinematic deformation model on the basis of the dense geodetically estimated velocities of the Lipari–Vulcano complex. In particular, the observed deformation pattern can be described by a combination of (1) the main N–S regional compression and (2) a NNE–SSW compression with a small right‐lateral strike slip component acting along a tectonic structure trending N°40W between the two islands. This pattern was inspected through a simplified synthetic model.     

Life-history- and ecosystem-driven variation in composition and residence pattern of seabream species (Perciformes: Sparidae) in two Mediterranean coastal lagoons

Species composition and length-frequency distributions of six sparid fish species were investigated in two central Mediterranean coastal lagoons off the western coast of Italy: Fogliano and Caprolace. In the former, the sparid fauna was dominated by the gilt-head seabream (Sparus aurata), whereas in Caprolace, species composition was more homogeneous across all six species. Size structure varied considerably among species: S. aurata, Diplodus puntazzo and Diplodus vulgaris had a single-cohort structure in both lagoons, whereas in Diplodus annularis and Diplodus sargus at least two cohorts were identified. In Lithognathus mormyrus inter-lagoon variation was detected, with a single-cohort structure in Fogliano and a two-cohort structure in Caprolace. While inter-specific differences can be explained by variation in life-history strategies among species, intra-specific variation in L. mormyrus is likely to be determined by the known differences between the two habitats: Fogliano being a more confined lagoon, and Caprolace more extensively influenced by the sea.     

Source parameters and scaling relationships in the Friuli-Venezia Giulia (Northeastern Italy) region

We estimated the source parameters of 53 local earthquakes (2.0<M_L<5.7) of the Friuli-Venezia Giulia (Northeastern Italy) area, recorded by the short-period local seismic network of the Istituto Nazionale di Oceanografia e Geofisica Sperimentale (OGS), in the period 1995-2003. Data were selected on the basis of high quality locations and focal mechanisms. Standard H/V spectral ratios (HVRS) of the three-component stations of the network were performed in order to assess local amplifications, and only stations showing HVRS not exceeding two were considered for the source parameters estimation. Both velocity and acceleration data were used to compute the SH-wave spectra. Observed spectra were corrected for attenuation effects using an independent regional estimate of the quality factor Q and a station dependent estimate of the spectral decay parameter k. Only earthquakes with M_L>3.0 recorded with a sampling rate of 125 cps were used to compute k, thus allowing to visualize a linear trend of the high frequency acceleration spectrum up to 40-50 Hz. SH-wave spectra, corrected for attenuation, showed an ω⁻² shape allowing a good fit with the Brune model. Seismic moments and Brune radii ranged between 1.5×10¹² and 1.1×10¹⁷  N m and between 0.1 and 2.7 km respectively. We obtained M_o=1.1×10¹⁷  N m for the seismic moment of the Kobarid (SLO) main shock, in good agreement with the Harvard CMT solution (M_o=3.5×10¹⁷  N m). Brune stress drops were confined to the range from 0.07 to 5.31 MPa, with an average value of 0.73 MPa and seem to be approximately constant over five orders of magnitude of seismic moment. Radiated seismic energy computed from two nearby stations scales with seismic moment according to , and apparent stress values are between 0.02 and 4.26 MPa. The observed scatter of Brune stress drop data allowed to hypothesize a scaling relation between seismic moment and corner frequency in order to accommodate both Brune stress drop and apparent stress scalings. No systematic differences are evidenced between stress parameters of earthquakes with different focal mechanisms. As a consequence, a relation of the seismic stress release with the strength of rocks can be hypothesized. A high correlation (r>0.9) of Brune stress drop is found with both apparent stress and RMS stress drop, according to and respectively.     

Physics and Seismic Modeling for Monitoring CO<Subscript>2</Subscript> Storage

We present a new petro-elastical and numerical-simulation methodology to compute synthetic seismograms for reservoirs subject to CO₂ sequestration. The petro-elastical equations model the seismic properties of reservoir rocks saturated with CO₂, methane, oil and brine. The gas properties are obtained from the van der Waals equation and we take into account the absorption of gas by oil and brine, as a function of the in situ pore pressure and temperature. The dry-rock bulk and shear moduli can be obtained either by calibration from real data or by using rock-physics models based on the Hertz-Mindlin and Hashin-Shtrikman theories. Mesoscopic attenuation due to fluids effects is quantified by using White's model of patchy saturation, and the wet-rock velocities are calculated with Gassmann equations by using an effective fluid modulus to describe the velocities predicted by White's model. The simulations are performed with a poro-viscoelastic modeling code based on Biot's theory, where viscoelasticity is described by generalizing the solid/fluid coupling modulus to a relaxation function. Using the pseudo-spectral method, which allows general material variability, a complete and accurate characterization of the reservoir can be obtained. A simulation, that considers the Utsira sand of the North Sea, illustrates the methodology.