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| Titel |
Natural versus anthropogenic subsidence of Venice: investigation of the present occurrence by PSI |
| VerfasserIn |
Luigi Tosi, Tazio Strozzi, Pietro Teatini |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250100644
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| Publikation (Nr.) |
 EGU/EGU2014-16630.pdf |
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| Zusammenfassung |
| We detected land displacements of Venice by Persistent Scatterer Interferometry (PSI)
using ERS and ENVISAT C-band and TerraSAR-X and COSMO-SkyMed X-band
acquisitions over the periods 1992–2010 and 2008–2011, respectively. PSI provides the
cumulative land displacements (natural plus anthropogenic) of the investigated area
independently of the radar band. The natural subsidence rate depends on the reference
period and, due to the present elevation of Venice with respect to the sea level, it is
much more interesting for the city to evaluate the natural displacement over the
last few decades, i.e. the present natural land subsidence, than that averaged over
geological periods. Concerning anthropogenic land subsidence the contribution due
to activities characterized by large scale and long term effects, e.g., that caused
by groundwater withdrawals, ended a few decades ago. Today, the anthropogenic
component of the land subsidence is only due to local, short-time interventions
such as restoration works and inherent deformations of historical structures. By
reason of the larger observation period, the C-band sensors were used to quantify the
long-term movements, i.e. the subsidence component primarily ascribed to natural
processes. The high resolution, short revisiting time X-band satellites reveal a high
effectiveness to monitor short-time movements as those induced by human activities. The
statistical analysis of the displacement distributions measured by PSI points out that
the average rates, i.e. the natural component of the subsidence, are almost equal
with the C-band and X-band satellites. Conversely, the standard deviation with
X-band acquisitions (1.6 mm/yr) is characterized by a value significantly larger
than that detected with C-band images (0.7 mm/yr). The larger X-band variability
superposes to a background velocity similar to that given by ERS/ENVISAT. It
is reasonable to assume that the difference between the movements provided by
ERS/ENVISAT and TerraSAR-X/COSMO-SkyMed is likely representative of the
effects caused by anthropogenic activities. This hypothesis is supported by a proper
processing of the two C and X-band measurements. The two datasets are interpolated by
the Kriging method on the same regular grid covering the whole city. The grid
spacing, fixed at 50 m, has been appropriately tuned to simultaneously i) filter out the
outlier values provided by the C-band analysis; and ii) keep the heterogeneity of the
displacements detected by the X-band investigation. Finally, the quantification of
man-induced displacements is obtained by removing the C-band interpolated map
from the X-band interpolated solution. The results show that a certain variability
characterizes the 1992-2010 natural subsidence (0.9 ± 0.7 mm/yr), mainly because of the
heterogeneous nature and age of the lagoon subsoil. The present anthropogenic
displacements occur at very local scale and are heterogeneously distributed with
values ranging from -10 and 2 mm/yr in 2008. They are caused by conservation
and reconstruction processes to preserve the building heritage together with urban
maintenance activities such as restoring the embankment walls to guarantee the stability of
the canal edges. Moreover, because the sinking zones are generally concentrated
along the main channels bounding and crossing the city, waves induced by the
intensive boat and ship traffic likely contribute by waking and eroding the fragile
masonry canal banks and the building foundations. Geotechnical applications such as
micropiles, anchors, jet grouting aimed at improving the subsoil characteristics are
likely responsible for the greater stability locally observed in some portions of the
city.
References
L. Tosi, P. Teatini, and T. Strozzi, Natural versus anthropogenic subsidence of Venice,
Nature Scientific Reports, 3:2710, doi:10.1038/srep02710, 2013. |
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