339 research outputs found
Spatial distribution of introduced brook trout Salvelinus fontinalis (Salmonidae) within alpine lakes: evidences from a fish eradication campaign
Brook trout Salvelinus fontinalis have been used worldwide to stock fishless alpine lakes, negatively affecting native biota. Understanding its spatial ecology in invaded ecosystems can provide information to interpret and contrast its ecological impact. We opportunistically used capture points of brook trout gillnetted during an eradication campaign to assess the distribution patterns of four unexploited populations inhabiting high-altitude lakes. The main eradication method implies the use of many gillnets with several mesh sizes, which are selective for different fish sizes. For each lake we drew six capture maps associated with as many different mesh sizes, and we tested whether the distance from the coastline (which in alpine lakes is a reliable proxy of the most important spatial gradients, e.g. depth, temperature, prey availability, lighting conditions) influences the proportion of captured fish belonging to different size classes and the number of fish captured by the nets with different mesh sizes. To interpret the results, we also provide a cartographic description of the lakes’ bathymetry and littoral microhabitats. We found (1) a negative relationship between brook trout distribution and the distance from the coastline in all of the size classes, lakes and mesh sizes; (2) that large brook trout can thrive in the lakes’ center, while small ones are limited to the littoral areas; and (3) that the distance from the coastline alone cannot explain all the differences in the catch densities in different parts of the lakes. As in their native range, introduced brook trout populations also have littoral habits. Microhabitats, prey availability and distance from the spawning ground are other likely factors determining the distribution patterns of brook trout populations introduced in alpine lakes. The obtained results also provide useful information on how to plan new eradication campaigns
Ups and downs in western Crete (Hellenic subduction zone)
Studies of past sea-level markers are commonly used to unveil the tectonic history and seismic behavior of subduction zones. We present new evidence on vertical motions of the Hellenic subduction zone as resulting from a suite of Late Pleistocene - Holocene shorelines in western Crete (Greece). Shoreline ages obtained by AMS radiocarbon dating of seashells, together with the reappraisal of shoreline ages from previous works, testify a long-term uplift rate of 2.5-2.7 mm/y. This average value, however, includes periods in which the vertical motions vary significantly: 2.6-3.2 mm/y subsidence rate from 42 ka to 23 ka, followed by ~7.7 mm/y sustained uplift rate from 23 ka to present. The last ~5 ky shows a relatively slower uplift rate of 3.0-3.3 mm/y, yet slightly higher than the long-term average. A preliminary tectonic model attempts at explaining these up and down motions by across-strike partitioning of fault activity in the subduction zone
Deep view of the Subduction-Transform Edge Propagator (STEP) fault in the Calabrian Subduction Zone
The Calabrian Subduction Zone plays a key role in the evolution of the central Mediterranean in the framework of
the convergence between Africa and Europe.
Here, the remnants of the World’s oldest oceanic crust form a narrow NW-dipping slab passively subducting
beneath the Calabrian Arc.
Recently published high-resolution seismic profiles and bathymetric data of the western Ionian Sea highlight
the presence of a NNW-SSE faulting system connected with a series of Plio-Pleistocene syn-tectonic basins.
These features are correlated with the recent activity of a major NNW-SSE deformation zone confining the active
subduction to the SW and interpreted as a Subduction-Transform Edge Propagator (STEP) fault.
The goal of this work is to jointly reconstruct the geometry of the STEP fault and the subduction interface in its
surroundings.We use multichannel seismic profiles acquired in the southwestern part of the Calabrian accretionary
wedge to focus on the STEP fault geometry at depth and to analyse its relationships with shallow deformation
features.
The quantitative analysis and enhancement of seismic data provided an accurate image of the internal structure
of the accretionary wedge at various depths, showing growth strata in the Plio-Pleistocene succession and major
discontinuities in the lower crust.
Our results depict a main subvertical, slightly east-dipping, lithospheric fault cutting the oceanic crust down to
the Moho, and a rich set of associated secondary synthetic and antithetic faults. This picture also provides new
insights on the STEP fault propagation mechanism.
In addition, the tridimensional correlation of the STEP fault occurrences in various seismic profiles provides
a preliminary scheme of its segmentation and highlights the relationships of this master fault with other main
structural elements of the Calabrian Arc and Eastern Sicily, including some of the faults deemed to be responsible
for major historical earthquakes in the area
Tsunami scenarios in the Mediterranean
We calculated the impact on Southern Italy of a large set of tsunamis resulting from earthquakes generated by major fault zones of the Mediterranean Sea. Our approach merges updated knowledge on the regional tectonic setting and scenario-like calculations of expected tsunami impact.
We selected three potential source zones located at short, intermediate and large distance from our target coastlines: the Southern Tyrrhenian thrust belt; the Tell-Atlas thrust belt; and the western Hellenic Arc. For each zone we determined a Maximum Credible Earthquake and described the geometry, kinematics and size of its associated Typical Fault. We then let the Typical Fault float along strike of its parent source zone and simulated all tsunamis it could trigger. Simulations are based on the solution of the nonlinear shallow water equations through a finite-difference technique. For each run we calculated the wave fields at desired simulation times and the maximum water elevation field, then produced travel-time maps and maximum wave-height profiles along the target coastlines.
The results show a highly variable impact for tsunamis generated by the different source zones. For example, a large Hellenic Arc earthquake will produce a much higher tsunami wave (up to 5 m) than those of the other two source zones (up to 1.5 m). This implies that tsunami scenarios for Mediterranean Sea countries must necessarily be computed at the scale of the entire basin. Our work represents a pilot study for constructing a basin-wide tsunami scenario database to be used for tsunami hazard assessment and early warning
Towards a seismogenic source model of the Dinarides
Geology-based seismogenic source models are becoming the fundamental input for seismic hazard assessment
at the scale of an entire country. In this work, we will illustrate in simple steps the complex process that leads
from basic data to a fully-fledged seismogenic source model of the Dinaride thrust belt, running along coastal
Croatia, Montenegro and part of Albania.
We started from a layer of basic geological and structural data and explored a wide range of indicators of recent
tectonic activity, such as drainage anomalies/diversions and displaced or warped geological markers. We then
analyzed the interplay of these indicators with known or prospective tectonic structures. To the picture thus
obtained, we added a layer with a revised historical seismic catalog and selected a few earthquakes for which
we re-estimate epicenter and magnitude. At the end of our analyses we combined all these data in a structured
GIS database. With these data at hand, we also compared the longer-term indicators with present-day
stress/strain data such as GPS velocities and earthquake focal solutions.
Following the approach already developed for the construction of the Database of Individual Seismogenic
Sources for Italy, we developed a seismogenic source model for the Dinarides in which the better constrained
seismogenic faults have been mapped and parameterized and made ready for use in seismic hazard practice.
We believe that our experience in the Dinarides will become useful in unifying and formalizing the process of
constructing seismic source models in other countries
The Database of Individual Seismogenic Sources (DISS), version 3: summarizing 20 years of research on Italy’s earthquake geology
This paper describes the main characteristics, the evolution, and the structure of the Database of Individual Seismogenic Sources (DISS) and particularly of its release of early 2007. The Database contains the results of the investigations of the active tectonics in Italy during the past
20 years. The first two sections of this paper document the recent evolution in mapping and archiving Italian active fault data in relation to important achievements in the understanding of Italian tectonics, some of which were spurred by significant earthquakes. The central sections
describe the current structure of the Database, the reasons for its assumptions and data categories, its current contents, its evolution through several years of improvements. The last section describes how the current contents of the Database correspond with the existing strain and stress data
available from focal mechanism, borehole breakout, and GPS data for the whole of Italy. The Database supplies a fresh and unified view of active and seismogenic processes in Italy by building on basic physical constraints concerning rates of crustal deformation, on the continuity of
deformation belts and on the spatial relationships between adjacent faults, both at the surface and at depth
Tsunamis scenarios in the Adriatic Sea
We calculated the expected impact on the Italian coast of the Adriatic Sea of a large set of tsunamis resulting from potential earthquakes generated by major fault zones. Our approach merges updated knowledge on the regional tectonics and scenario-like calculations of expected tsunami impact.
We selected six elongated potential source zones. For each of them we determined a Maximum Credible Earthquake and the associated Typical Fault, described by its size, geometry and kinematics. We then let the Typical Fault float along strike of its parent source zone and simulated all tsunamis it could generate. Simulations are based on the solution of the nonlinear shallow water equations through a finite-difference technique. For each run we calculated the wave fields at specified simulation times and the maximum water height field (above mean sea level), then generated travel-time maps and maximum wave height profiles along the target coastline. Maxima were also classified in a three-level code of expected tsunami threat.
We found that the southern portion of Apulia facing Albania and the Gargano promontory are especially prone to the tsunami threat. We also found that some bathymetric features are crucial in determining the focalization-defocalization of tsunami energy. We suggest that our results be taken into account in the design of early-warning strategies
Integrating geologic fault data into tsunami hazard studies
We present the realization of a fault-source data set designed to become the starting point in regional-scale tsunami hazard studies. Our approach focuses on the parametric fault characterization in terms of geometry, kinematics, and assessment of activity rates, and includes a systematic classification in six justification levels of epistemic uncertainty related with the existence and behaviour of fault sources. We set up a case study in the central Mediterranean Sea, an area at the intersection of the European, African, and Aegean plates, characterized by a complex and debated tectonic structure and where several tsunamis occurred in the past. Using tsunami scenarios of maximum wave height due to crustal earthquakes (Mw=7) and subduction earthquakes (Mw=7 and Mw=8), we illustrate first-order consequences of critical choices in addressing the seismogenic and tsunamigenic potentials of fault sources. Although tsunamis generated by Mw=8 earthquakes predictably affect the entire basin, the impact of tsunamis generated by Mw=7 earthquakes on either crustal or subduction fault sources can still be strong at many locales. Such scenarios show how the relative location/orientation of faults with respect to target coastlines coupled with bathymetric features suggest avoiding the preselection of fault sources without addressing their possible impact onto hazard analysis results
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