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| Titel |
Paleoseismological multi-theme study of seismically induced geological effects at Vendicari (south-eastern Sicily). |
| VerfasserIn |
Claudia Pirrotta, Maria Serafina Barbano |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250032167
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| Zusammenfassung |
| Strong earthquakes can produce direct and permanent geological effects on the earth surface.
Beyond surface faulting, other effects, such as landslides, liquefactions and ground
deformations (seismites), take place in the epicentral area as a consequence of the seismic
wave propagation in the sediments. Since the last three decades only, these features have been
considered indicators of seismicity and their analysis (paleoseismological off-fault study) has
been used as an useful tool for obtaining crucial information on the causative earthquake
parameters. Such analyses are especially useful in areas where earthquakes occurred
before the seismic instrument development or without clear evidence of surface
faulting. Since paleoseismology is a youth discipline, the integration of innovative and
multidisciplinary techniques and the updating of the case studies on seismites is of
fundamental importance.
During historical time south-eastern Sicily has been hit by strong earthquakes (M up to
7), such as the 1169, 1542 and 1693 events. Given the lack of surface faulting evidence, the
real source location of these earthquakes is a still open question and represents the main gap
of the Sicilian seismogenic framework, therefore paleosismological off-fault study can
contribute to identify seismogenic sources.
Along the NNE-SSW trending rocky coast of Vendicari, we detected a singular
association of deformational structures affecting terrains up to Quaternary age. These
structures are both soft sediment deformations (autoclastic breccias, diapyr-like injections,
dikes and thyxotropic wedges), probably linked to liquefaction mechanisms, and fragile
deformations, consisting of opened fractures generally filled by sediment (Neptunian dykes).
With the aim to define the deformation mechanisms that affected the deposits at Vendicari,
we studied in detail the local stratigraphic sequence and the deformational structures,
performing a mesostructural study of the fractures and the analysis of the microscopic
characteristic of the filling materials, as well.
The systematic and paleostress analyses of the fractures highlighted a high variability in
the architectural style and a high dispersion of the plane direction. This is probably linked to
more than one deformative mechanism concurring in their development and masking the
stress field. A coseismic brittle deformation, linked to the shaking and to the seismic wave
propagation, and a lateral spreading and settlement mechanism with fissuring parallel
to the coastline (driven by gravity under a moderate topographic gradients), are
proposed as probable causes of the fracture development together with the tectonic
stress field. However, the analysis of the fractures, filtered and cleaned up from
the contribute of the disturb mechanisms, shows a stress field characterized by a
probable NW-SE-trending Ï1,which iscompatible with the active regional stress. The
occurrence of violent coseismic deformation should be also testified by the development
of the liquefaction-driven soft sediment deformations, observed in the area, that
reveals the application of an horizontal shear stress and of a sudden high hydraulic
pressure.
The overall analysis of seismites at Vendicari highlights the occurrence of at least three
triggering events, occurred after the Pleistocene age. They could be tentatively associate
with the historical 1169, 1542 and 1693 earthquakes (I0 -¥X) or with similar or
strongest paleoevents, considering the minimum epicentral distances and the minimum
intensity at a site (Is -¥ IX) for which an earthquake is capable to induce these
association of seismites. The paleoseismological study at Vendicari allowed us
to upgrade the paleoseimological off-fault techniques and to increase the study
cases in Sicily. Moreover, this study provides, if integrated with similar studies at
regional scale, new and useful information on ancient earthquakes in a high-seismicity
area like eastern Sicily, for a better characterization of the seismogenic sources. |
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