Present activity and seismogenic potential of a low-angle normal fault system (Città di Castello,Italy): Constraints from surface geology,seismic reflection data and seismicity

We present new constraints on an active low-angle normal fault system in the Città di Castello–Sansepolcro basin (CSB) of the northern Apennines of Italy. New field data from the geological survey of the Carta Geologica d'Italia (CARG project) define the surface geometry of the normal fault system and lead to an interpretation of the CROP 03 deep-crust seismic reflection profile (Castiglion Fiorentino–Urbania segment), with particular attention paid to the geometry of the Plio-Quaternary extensional structures. Surface and sub-surface geological data are integrated with instrumental and historical seismicity in order to define the seismotectonics of the area.Low-angle east-dipping reflectors are the seismic expression of the well-known Altotiberina Fault (AF), a regional extensional detachment on which both east- and west-dipping high-angle faults, bounding the CSB, sole out. The AF breakaway zone is located ～ 10 km west of the CSB. Within the extensional allochthon, synthetic east-dipping planes prevail. Displacement along the AF is ～ 4.5 km, which agrees with the cumulative offset due to its synthetic splays. The evolution of the CSB has mainly been controlled by the east-dipping fault system, at least since Early Pleistocene time; this system is still active and responsible for the seismicity of the area. A low level of seismic activity was recorded instrumentally within the CSB, but several damaging earthquakes have occurred in historical times. The instrumental seismicity and the intensity data points of the largest historical earthquakes (5 events with maximum MCS intensity of IX to IX–X) allow us to propose two main seismogenic structures: the Monte Santa Maria Tiberina (Mmax = 5.9) and Città di Castello (Mmax up to 6.5) normal faults. Both are synthetic splays of the AF detachment, dipping to the NE at moderate (45–50°) to low (25–30°) angles and cutting the upper crust up to the surface. This study suggests that low-angle normal faults (at least with dips of 25–30°) may be seismogenic.     

Imposex levels and concentrations of organotin compounds (TBT and its metabolites) in Nassarius nitidus from the Lagoon of Venice

Specimens of Nassarius nitidus were collected in seven stations of the Venice Lagoon to assess the levels of tributyltin (TBT) and its metabolites monobutyltin and dibutyltin in the tissues and monitor their effect on organisms, in particular the phenomenon of imposex (superimposition of male sexual characteristics on females). The following values of population indices were found: vas deferens sequence: 1.2+/-0.7-4.0+/-0.5; relative penis length: 6-47%. The least impacted station was situated in the northern part of the Lagoon, where females without imposex were found and Butyltin (BuTs) concentrations in the organisms (average sum of BuTs=43+/-14 ngSng(-1)w.) were significantly lower than in the other stations (range of average sum of BuTs: 101+/-22-217+/-27 ngSng(-1)d.w.). Population indices were found to be related to the TBT content in the tissues. In particular VDSI had a significant logarithmic correlation: r=0.95, n=8, p<0.05.     

Imposex levels and concentrations of organotin compounds (TBT and its metabolites) in Nassarius nitidus from the Lagoon of Venice

Specimens of Nassarius nitidus were collected in seven stations of the Venice Lagoon to assess the levels of tributyltin (TBT) and its metabolites monobutyltin and dibutyltin in the tissues and monitor their effect on organisms, in particular the phenomenon of imposex (superimposition of male sexual characteristics on females). The following values of population indices were found: vas deferens sequence: 1.2 ± 0.7–4.0 ± 0.5; relative penis length: 6–47%. The least impacted station was situated in the northern part of the Lagoon, where females without imposex were found and Butyltin (BuTs) concentrations in the organisms (average sum of BuTs = 43 ± 14 ng Sn g⁻¹ w.) were significantly lower than in the other stations (range of average sum of BuTs: 101 ± 22–217 ± 27 ng Sn g⁻¹ d.w.). Population indices were found to be related to the TBT content in the tissues. In particular VDSI had a significant logarithmic correlation: r = 0.95, n = 8, p < 0.05.     

On the influence of reflection over a rhythmic swash zone on surf zone dynamics

The reflection of incident gravity waves over an irregular swash zone morphology and the resulting influence on surf zone dynamics remains mostly unexplored. The wave-phase resolving SWASH model is applied to investigate this feedback using realistic low-tide terraced beach morphology with well-developed beach cusps. The rhythmic reflection generates a standing wave that mimics a subharmonic edge wave, from the superimposition of incident and two-dimensional reflected waves. This mechanism is enhanced by shore-normal, narrow-banded waves in both direction and frequency. Our study suggests that wave reflection over steep beaches could be a mechanism for the development of rhythmic morphological features such as beach cusps and rip currents.     

In situ oxygen uptake rates by coastal sediments under the influence of the Rhône River (NW Mediterranean Sea)

The influence of riverine inputs on biogeochemical cycling and organic matter recycling in sediments on the continental shelf off the Rhône River mouth (NW Mediterranean Sea) was investigated by measuring sediment oxygen uptake rates using a combination of in situ and laboratory techniques. Four stations were investigated during two cruises in June 2001 and June 2002, with depths ranging from 9 to 192 m and over a distance to the Rhône River mouth ranging from 4 to 36 km. Diffusive oxygen uptake (DOU) rates were determined using an in situ sediment microprofiler and total oxygen uptake (TOU) rates were measured using sediment core incubations. There was good agreement between these two techniques which indicates that the non-diffusive fraction of the oxygen flux was minimal at the investigated stations. DOU rates ranged from 3.7±0.4 mmol O₂ m⁻² d⁻¹ at the continental shelf break to 19.3±0.5 mmol O₂ m⁻² d⁻¹ in front of the Rhône River mouth. Sediment oxygen uptake rates mostly decreased with increasing depth and with distance from the Rhône mouth. The highest oxygen uptake rate was observed at 63 m on the Rhône prodelta, corresponding to intense remineralization of organic matter. This oxygen uptake rate was much larger than expected for the increasing bathymetry, which indicates that biogeochemical cycles and benthic deposition are largely influenced by the Rhône River inputs. This functioning was also supported by the detailed spatial distribution of total organic carbon (TOC), total nitrogen (TN) and C/N atomic ratio in surficial sediments. Sediments of the Rhône prodelta are enriched in organic carbon (2–2.2%) relative to the continental shelf sediments (<1%) and showed C/N ratios exceeding Redfield stoichiometry for fresh marine organic matter. A positive exponential correlation was found between DOU and TOC contents (r²=0.98, n=4). South-westward of the Rhône River mouth, sediments contained highly degraded organic matter of both terrestrial and marine origin, due to direct inputs from the Rhône River, sedimentation of marine organic matter and organic material redeposition after resuspension events.     

Measuring molecular variation in zooplankton populations: DNA extraction from smallDaphnia species

We present methods developed for the small-sizedDaphnia species,D. galeata, D. hyalina, D. cucullata, and their hybrids, which facilitate the use of DNA variation in population studies. Described are large-scale production of material from single genotypes ofDaphnia and subsequent extraction of total DNA. The average DNA yields ranged between 6 µg per gram wet weight (D. cucullata) and 12 µg per gram wet weight (D. galeata). For comparison, the large-sized speciesD. pulex was tested and yielded an average of 28 µg DNA per gram wet weight. The DNA isolated in this manner lends itself well to molecular genetic techniques suited for population studies.Reprint requests to B. Streit.     

Bathymetric control of surf zone retention on a rip-channelled beach

Simulations from a numerical model address the impact of nearshore morphology on surf zone retention on, open coast, rip-channelled beaches exposed to shore-normal waves. In the model, rip channels are regularly spaced alongshore with a given spacing λ. For a given reference case bathymetry (λ= 200 m), rip current circulations retain floating material at a hourly rate R of about 80 % which is in line with most existing field and laboratory studies in similar settings. The influence of a surf zone rip-channel morphology on surf zone retention is evaluated by a number of morphologic parameters. Results show that rip spacing is important. The ratio of the surf zone width X _s to rip spacing λ controls surf zone retention with R rapidly increasing with increasing X _s /λ up to a threshold of about 1 above which R levels off to become asymptotic to 100 %. The impact of the presence of a rip head bar is profound but nonlinear. The onset of wave breaking across the rip head bar drives a weak seaward located circulation providing major pathways for surface water exiting the surf zone compartment. Additional simulations suggest that alongshore variations in the offshore bathymetry are important. Patterns in the wave field enforced by wave refraction and potentially wave breaking across offshore bathymetric anomalies can provide a conduit for transporting floating material out of the surf zone and into the inner shelf region. This has major implications for surf zone flushing by inner-bar rips on multiple-barred beaches and on beaches facing bathymetric anomalies on the inner shelf.     

Boundedness of Turbulent Temperature Probability Distributions,and their Relation to the Vertical Profile in the Convective Boundary Layer

Higher-order moments, minima and maxima of turbulent temperature and water vapour mixing ratio probability density functions measured with an eddy-covariance system near the ground were related to each other and to vertical boundary-layer profiles of the same scalars obtained through airborne soundings. The dependence of kurtosis on squared skewness showed a kurtosis intercept below the Gaussian expectation, suggesting a compression of the probability density function by the presence of natural boundaries. This hypothesis was corroborated by comparing actual minima and maxima of turbulent fluctuations to estimates obtained from the first four sample moments by fitting a four-parameter beta distribution. The most sharply defined boundaries were found for the minima of temperature datasets during the day, indicating that negative temperature fluctuations at the sensor are limited by the availability of lower temperatures in the boundary layer. By comparison to vertical profiles, it could be verified that the turbulent minimum of temperature near the ground is close to the minimum of potential temperature in the boundary layer. The turbulent minimum of water vapour mixing ratio was found to be equal to the mixing ratio at a height above the minimum of the temperature profile. This height roughly agrees with the top of the non-local unstable domain according to bulk Richardson number profiles. We conclude that turbulence statistics measured near the surface cannot be solely explained by local effects, but contain information about the whole boundary layer including the entrainment zone.     

A comparison among olive flowering trends in different Mediterranean areas (south-central Italy) in relation to meteorological variations

Phenological observations of the anthesic phases of olive flowering in a central Mediterranean area were recorded over a 9-year period. The aim of this research was to compare the flowering dates in relationship to the meteorological changes. Pollen emission from anthers was monitored by remote instrumentation placed directly in olive groves and phenological data regarding daily pollen concentrations (pollen/m³) were recorded using a pollen monitoring methodology. The rhythm of the phenological phases emerged as dependent on the meteorological trend of the spring forcing temperature. Generally, the phenomenon of pollen emission occurred progressively earlier prior to 2001, while in the following 5 years, the trend seemed to be inverted, showing a progressive delay of flowering. The spring quarterly mean temperature trends registered by GISS data in Europe confirmed the presence of diverse meteorological behavior during the study period, probably causing the biological divergences that were monitored. The principal result of the present contribution is to evidence the relativity of empirical investigations and observations considering different time intervals. This is due to the partial, brief series (9 years) of flowering dates which have to be considered as part of a longer series (26 years) in order to have a complete vision of the true phenomenon.