IASPEI - Picture Gallery

IUGG XXIV General Assembly July 2-13, 2007 Perugia, Italy
(S) - IASPEI - International Association of Seismology and Physics of the Earth's
Interior
JSS014 Poster presentation 2304
Short term (geodetic) and long term (geological) deformation patterns in
the Northern Apennines
Dr. Nicola Cenni
Physics - Sector of Geophysics University of Bologna
Paolo Baldi, Enzo Mantovani, Maurizio Ferrini, Marcello Viti, Vittorio D'Intinosante,
Daniele Babbuci, Dario Albarello
The Northern Apennines are constituted by remnants of the Alpine belt and by younger accretionary
units stacked along the consuming border of the Adriatic domain. Present seismotectonic activity,
associated with normal faults, is mostly concentrated in the axial part of the chain, where a NW-SE
alignement of troughs is located. It is widely recognized that the average long-term displacement
pattern could be significantly different from the short-term one, due to transient effects of post-seismic
relaxation induced by strong earthquakes at major decoupling zones. A tentative estimate of both the
short and long term behaviours is tried by mean of geodetic measurements and analysis of neotectonic
deformation respectively. A reliable estimate of the velocity field in a zone is strongly conditioned by the
high density of the geodetic network. This is particularly true for regions, like the Apennines belt, which
are characterized by a complex tectonic setting and a strongly heterogenous strain pattern. In
theNorthern Apenninesregion a densification of the national geodetic network has been recently
achieved by the installation of 8 GPS permanent stations, with the financial support of the Regione
Toscana. The observations collected by these stations have been processed together with the ones
provided by other 20 permanent stations in the surrounding regions which observed almost
continuously from 2001 to 2006. Double-differenced phase measurements have been processed with
the GAMIT software version 10.31 as single daily solutions. In data elaboration we have held fixed IGS
final orbits, used coherent earth orientation parameters, removed outliers and cycle slips, estimated and
applied tropospheric and ionospheric corrections and carried out a least square adjustment of the
baseline elements. The present velocity field inferred from GPS data indicates that the central sector of
the Apennines belt, the Umbro-Marchigiane-Romagnole Units, moves with a significantly higher velocity
with respect to the adjacent sectors of that arc. This result is fairly consistent with the long term
pattern, deduced by the time-space distribution of recent deformation (Quaternary). The reconstruction
of this last pattern has also been carried out by a quantitative approach, based on finite element
modelling. Both the short and long term patterns are consistent with the strain field inferred from the
analysis of focal mechanisms of earthquakes. The geodynamic setting in the central Mediterranean
region and the distribution of major earthquakes in the Apennines belt during the last centuries suggest
that seismotectonic activity in the Northern Apennines is strongly influenced by the most intense
decoupling earthquakes in the Latium-Abruzzi platform (Central Apennines). Since that platform has not
been affected by strong earthquakes in the last 90 years, we suppose that this relatively long
quiescence could explain the similarity between short and long term velocity and strain fields in the
study area.
Keywords: gps, northern apennines, geological geodetic strain