Geoscience Reference
In-Depth Information
Fig. 2.50
Principal hole of
Spring of Vaucluse in summer
season (low water level)
field are the fault-plane solutions from earthquakes
(ex.: Mattauer and Mercier
1980
). Every fault-plane
solution for a given earthquake focus is closely rela-
ted to the local tectonic conditions. They often show a
remarkable coherence for large areas. The concen-
tration or the alignment of epicenters of weak earth-
quakes
and the corresponding interpretation, two tectonic
stress fields have been reconstructed, both having
remarkable coherence in directions of maximum and
minimum tectonic stress axes for the different sites.
The characteristic feature of both stress fields is the
sub-horizontal position of the maximum and minimum
stress axes. The problem was to determine the relative
age of every one of the tectonic stress fields.
The elaboration of rose-diagrams, indicating the
preferential directions of the horizontal galleries, has
been made using the maps of the cave galleries in the
region (Fage,
1981
). It is evident (Fig.
2.51
) that, in
general, the NE-SW direction is preferential and
there is a close relationship between the open frac-
tures, indicated on Table
2.8
as product of the Post-
Burdiganian Phase, and the karst galleries. This
direction is also well marked by the general strike of
the youngest faults.
The scheme of these faults is elaborated on the
base of two principal sources of information—The
Map of Remote Sensing Lineaments of France in a
scale 1:1 000 000 (Scanvic and Weecksteen
1984
)
and the Seismotectonic Map of France (Voght and
Godefroy
1981
). The lineaments from satellite images
could be accepted under some conditions as traces of
reactivated faults or faults formed during the neo-
tectonic stage and active up to now. The faults from
the Seismotectonic Map are interpreted as structures,
in
some
territories
helps
to
detect
the
contemporary active tectonic zones.
Satellite Laser Ranging Geodetic Solutions
The Grasse laser tracking station velocity (SE France)
is derived from the analysis of 977,000 normal points
of the geodynamic satellite Lageos-1 covered the data
span of 16 years—from January 1984 till December
1999 (Shanov and Georgiev
2001
). The data reduc-
tion and analysis procedure were performed by the
SLRP 3.2 software for dynamic orbital analysis and
least-square parameter estimation (Georgiev and
Kotzev
1995
) using the recent dynamicmodels
and fundamental constants (McCarthy
1996
).
2.3.4.3 Tectonic Stress Fields and Analyses
of Their Control on the Karst
System
Data on shear joints analysis from the limestones of the
plateau have been collected from five outcrops
(Fig.
2.51
). The elements of 100 joints at least were
measured on every site. After mathematical processing
