The earth is in continuous movement, on time scales of some
fraction of second, to almost static movements. These movements give way to a
deformation of the crust that can be observed with very sensitive instruments,
as the ones of the
Grotta
Gigante and of the
Friuli strain-tilt
network. Measurements made underground, record
weak signals that cannot be detected otherwise. Some examples are the earth
tides due to moon-solar gravitational forces, the deformation due to the weight
of the oceans or the atmospheric pressure column, the deformations due to
surface or subsurface water movements, the eigen-vibrations of the earth, the
deformations that accompany the build-up of an earthquake, and in general all
deformations related to tectonic plates movements. We are interested in all
topics related to the observation, modeling and interpretation of these
signals.
Seismic
precursors
A great challenge in Geophysics is to be able to give some
prediction regarding the realization of a seismic event. The problem is
approached by direct instrumental monitoring of endangered areas and by
statistical evaluation of the seismicity in time and space. The observation of
deformation by geodetic instrumentation (tilt and strain meters, GPS) is one
experimental method, and a great problem is to determine very carefully what the
effects are that disturb the observations, as is the atmospheric pressure, the
water table variations, the temperature, and the rainfall. The great pendulums
gave interesting signals in the three years preceding the 1976 disastrous Friuli
earthquake: starting with 1973 a disturbing signal appeared on both the NS and
EW pendulums, that intensified the amplitude and duration until 1976, when it
stopped suddenly with event. In the months later the signals appered again, but
gradually expired, and have not been observed since.
Deformation
anisotropies
The welth of deformational data collected by the
Friuli strain-tilt network instruments in the last
25 years, since the most recent Friuli destructive earthquake, provide an
excellent opportunity to construct an anisotropic model of the uppermost Earth's
crust in the area to describe its seasonal behavioural peculiarities.
Lithospheric
flexure
The lithospheric flexure model is based on the deformation of a
thin elastic plate by loading on the top, bottom or within the plate. The
deformation of the plate depends on the flexural parameters which can be
determined by analyzing the crustal loads and the crustal deflection. The
flexural parameters vary spatially and have characteristic values in different
parts of the earth. Over sea areas the flexural rigidity depends on the age of
the ocean plate at the time of loading. Combined with the gravity inversion the
flexure analysis becomes a powerful system to study the earth structure. Flexure
studies require application of 2D spectral analysis and 2D filtering
methodologies.