Geoscience Reference
In-Depth Information
Fig. 2.51
Geological
scheme of Plateau of
Vaucluse with elements of
geodynamics (after Shanov
and Cousset
1993
; Shanov
and Georgiev
2001
)
1—Bedoulien terrain;
2—Lower Cretaceous
limestones; 3—Neocomian
marls; 4—fault; 5—normal
fault; 6—front of thrusting;
7—remote sensing
lineaments; 8—earthquake
epicenters (magnitudes
M
L
= 1.0-3.0 and time
interval from 1982 to
September 2013); 9—cave
location with rose-diagram of
the karst galleries; 10—point
of mass measurements of
joints
connected directly to the present day tectonic pro-
cesses. They could be distributors of the seismic
energy or generators of this energy. For the monts of
Vaucluse and Ventoux a clear coincidence exists
between the main strike of these faults (NE-SW) and
the preferred direction of karst processes, in spite of
the well-developed fault system with general trend
NW-SE (see Fig.
2.49
). Such a result has been dis-
cussed for the whole region (Mudry and Puig
1991
).
The NW-SE fault direction is probably a result of the
oldest tectonic stress field that has deformed the
limestones during the earlier stage of their diagenesis.
This is reflected in the reconstructed direction of
compression using the stylolite indentation (Shanov
and Cousset
1993
).
Processes of formation of young NE-SW striking
faults are also reflected by the chain arrangement of
earthquake epicenters to the northwest of Mont
Ventoux (Fig.
2.51
). The earthquakes are of low
magnitudes (less than M
L
= 3.0). But, the most
important confirmation for the existence of contem-
porary compressive NE-SW directed strain for this
region is the result of the fault-plane solutions from
the earthquakes (Shanov and Georgiev
2001
). The
fault-plane solutions from earthquakes northeast of
the studied region show, as a general rule, orientation
of the maximum strain compatible to the maximum
stress axis of the youngest tectonic stress field,
reflected by the joint systems of the limestones (see
Table
2.8
).
The absolute velocity vectors for the site GRASSE
displacement, the nearest Laser Tracking Site,
according to the NOVEL1A model and to the Satelite
Laser Ranging global geodetic solution, demonstrate
practically the same orientation and the velocity range
of about 25 mm/year toward northeast and this is the
general trend for the western part of the Eurasian
Plate (Table
2.8
). There is a small residual motion
with respect to Eurasia of about 4-5 mm/year in
southeastern direction (Shanov and Georgiev
2001
).
The absolute site motion is in good agreement with
the general direction of the P-axes from the earth-
quake fault-plane solutions, and this could be inter-
preted
as
an
evidence
for
the
direct
relationship
