Seismic anisotropy reveals focused mantle flow around the Calabrian slab (Southern Italy)

SKS splitting at the Calabrian subduction zone, with delay times (δt) up to 3s, reveals the presence of a strong anisotropic fabric. Fast directions (ϕ) are oriented NNE-SSW in the Calabrian Arc (C.A.) and rotate NNW-SSE to the north following the arcuate shape of the subducting plate. We interpret the trench-parallel ϕ as local-scale mantle flow driven by the retrograde motion of the slab; the absence of trench perpendicular ϕ below the Southern Apennines (S.A.) excludes the presence of a seismically detectable return flow at its NE edge. This may be due to the relative youth and limited width of the S.A. slab tear. A possible return flow is identified farther north at the boundary of the S.A. and Central Apennines. Different and weaker anisotropy is present below the Apulian Platform (A.P.). This implies that the influence of the slab rollback in the sub-slab mantle is limited to less then 100 km from the slab

SKS splitting in Southern Italy: anisotropy variations in a fragmented subduction zone.

In this paper we present a collection of good quality shear wave splitting measurements in Southern Italy. In addition to a large amount of previous splitting measurements, we present new data from 15 teleseisms recorded from 2003 to 2006 at the 40 stations of the CAT/SCAN temporary network. These new measurements provide additional constraints on the anisotropic behaviour of the study region and better define the fast directions in the southern part of the Apulian Platform. For our analysis we have selected wellrecorded SKS phases and we have used the method of Silver and Chan to obtain the splitting parameters: the azimuth of the fast polarized shear wave (φ) and delay time (δt). Shear wave splitting results reveal the presence of a strong seismic anisotropy in the subduction system below the region. Three different geological and geodynamic regions are characterized by different anisotropic parameters. The Calabrian Arc domain has fast directions oriented NNE–SSW and the Southern Apennines domain has fast directions oriented NNW–SSE. This rotation of fast axes, following the arcuate shape of the slab, is marked by a lack of resolved measurements which occurs at the transition zone between those two domains. The third domain is identified in the Apulian Platform: here fast directions are oriented almost N–S in the northern part and NNE–SSW to ENE–WSW in the southern one. The large number of splitting parameters evaluated for events coming from different back-azimuth allows us to hypothesize the presence of a depth-dependent anisotropic structure which should be more complicated than a simple 2 layer model below the Southern Apennines and the Calabrian Arc domains and to constrain at 50 km depth the upper limit of the anisotropic layer, at least at the edge of Southern Apennines and Apulian Platform. We interpret the variability in fast directions as related to the fragmented subduction system in the mantle of this region. The trench-parallel φ observed in Calabrian Arc and in Southern Apennines has its main source in the asthenospheric flow below the slab likely due to the pressure induced by the retrograde motion of the slab itself. The pattern of φ in the Apulian Platform does not appear to be the direct result of the rollback motion of the slab, whose influence is limited to about 100 km from the slab. The anisotropy in the Apulian Platform may be related to an asthenospheric flow deflected by the complicated structure of the Adriatic microplate or may also be explained as frozen-in lithospheric anisotropy

Do wholes become more than the sum of their parts in the rodent (Rattus Norvegicus) visual system? A test case with the configural superiority effect

The rodent has been used to model various aspects of the human visual system, but it is unclear to what extent human visual perception can be modelled in the rodent. Research suggests rodents can perform invariant object recognition tasks in a manner comparable to humans. There is further evidence that rodents also make use of certain grouping cues, but when performing a shape discrimination they have a tendency to rely much more on local image cues than human participants. In the current work, we exploit the fact that humans sometimes discriminate better between whole shapes, rather than the parts from which they are constructed, to ask whether rodents show a classic Configural Superiority Effect. Using touchscreen-equipped operant boxes, rats were trained to discriminate ‘part’ or ‘whole’ images based off of those used by J. R. Pomerantz et al. (1977) J Exp Psychol Hum Percept Perform, 3, 422–435. Here, we show that rats show no advantage for wholes and that they perform better when presented with simpler image parts, a pattern of effect opposite to what was seen in humans when highly comparable stimuli were used. These results add to our understanding of the similarities and differences between the human and rodent visual system, and suggest that the rodent visual system may not compute part whole relationships in a way comparable to humans. These results are significant from both a comparative anatomy perspective, and of particular relevance for those wishing to use rodents to model visuo-perceptual deficits associated with human psychiatric disorders

Shear wave splitting in southern tyrrhenian subduction zone (Italy) from CESIS and CAT/SCAN projects

In the years 2003 -2006 several broad band stations were installed in Southern Italy: 15 permanent ones (CESIS project), improved the INGV Italian national network and 40 temporary ones were installed in the frame of CAT/SCAN NSF project.We present shear wave splitting measurements obtained analyzing SKS phases and local S phases from slab earthquakes. We used the method of Silver & Chan to obtain shear wave splitting parameters: fast direction and delay time. Shear wave splitting measurements reveals strong seismic anisotropy in the mantle beneath Southern Tyrrhenian subduction system. The SKS splitting results show fast polarization directions varying from NNW-SSE in the Southern Apennines to N-S and to E-SW in Calabria, following the strike of the mountain chain. Moving toward the Adriatic sea the fast directions rotate from N-S to NE-SW. Fast directions could indicate the mantle flow below the slab, due to its retrograde motion but also the lithospheric fabric of the subducting plate. In the Tyrrhenian domain, above the slab, from Sardinia to the Italian and Sicilian coasts the dominant fast direction is E-W and could be related to the opening of the Tyrrhenian basin and to the corner flow in the asthenospheric wedge. In Sicily fast directions depict a ring around the slab edge supporting the existence of a slab tear and of a return flow from the back to the front of the slab. Measurements obtained with intermediate and deep earthquakes slab S phases show an extremely complex pattern of fast directions. They are mostly distributed in front of the Tyrrhenian Calabrian coast in correspondence of the fast velocity anomaly imaged at 150 km depth by tomography. We can relate this fast directions variability to the complex structure of the slab itself. The complex pattern of SKS and S splitting measurements suggests the presence of local scale mantle flow controled by the motion of an anisotropic slab

Methodology for developing and implementing alternative temperature-time curves for testing the fire resistance of barriers for nuclear power plant applications

Advances in fire science over the past 40 years have offered the potential for developing technically sound alternative temperature-time curves for use in evaluating fire barriers for areas where fire exposures can be expected to be significantly different than the ASTM E-119 standard temperature-time exposure. This report summarizes the development of the ASTM E-119, standard temperature-time curve, and the efforts by the federal government and the petrochemical industry to develop alternative fire endurance curves for specific applications. The report also provides a framework for the development of alternative curves for application at nuclear power plants. The staff has concluded that in view of the effort necessary for the development of nuclear power plant specific temperature-time curves, such curves are not a viable approach for resolving the issues concerning Thermo-Lag fire barriers. However, the approach may be useful to licensees in the development of performance-based fire protection methods in the future

SKS splittings in the southern Apennines-Calabrian arc region (southern Italy)

During the years 2003-2006 CAT/SCAN (Calbarian-Apennine-TyrrhenianlSubductionCollision- Accretion Network) temporary broadband stations operate in Southern Apennine and Calabria (Italy). In the same period CESIS-INGV project improved the number of permanent seismic stations in the same area. We analyze the data recorded to study seismic anisotropy and to investigate the mantle flow in the boun(fary-zoile{ between Southern Apennine and Calabriaibeneath and above the subducting slab. In the current work we present new shear wave splittings obtained analyzing SKS phases of 15 teleseisms with epicentral distance ranging from 88.40 to 98.20 and magnitude greater than 6.0. We used the method of Silver & Chan (1991) to obtained anisotropic parameters: delay time and fast polarization direction. The splitting parameters reveal strong seismic anisotropy in the mantle beneath Southern Tyrrhenian Sea- Calabrian Arc System that seems to be controlled by the slab presence. The clear variability in the fast directions allow us to hypothesize the existence of different anisotropic domains: fast polarization directions vary from NNW -SSE in the tyrrhenian side ofthe Southern Apennine to N-S and NE-SW toward the Adriatic Sea. Moving toward the Calabria fast directions are prevalently trench parallel showing a NE-SW orientation following the strike on the mountain chain

Prospectus, August 21, 2000

https://spark.parkland.edu/prospectus_2000/1019/thumbnail.jp

Crustal Structure in the Southern Apennines from Teleseismic Receiver Functions

While the upper structure of the Southern Apennines is known, lack of control on the deep structure allows competing thin-skin and tick-skin models of the orogen. In thin-skin models the detachment decouples a stack of rootless nappes from the basement. In the tick-skin models, besement is involved in the most recent phase of thrusting. To examine crustal structure, we use teleseismic data from the CAT/SCAN array in southern Italy. We use receiver functions (RF) processed into a Common Conversion Point (CCP) stack to generate images of the crust. Interpretation and correlation to geological structure is done using inversions of individual station RFs. We focus on a shallow discontinuity where P-to-S conversions occur. In the foreland, it corresponds to velocity jumps between carbonate and clastic strata with basement. A similar interpretation for the Apennines provides the most parsimonious explanation and supports a tick-skin interpretation. In a thick-skin reconstruction, the amount of shortening is much smaller than for a thin-skin model. This implies considerably less Plio-Pleistocene shortening across the Apennines and suggests an E-SE motion of the Calabrian Arc subparallel to the southern Apennines rather than a radial expansion of the Arc