RÉSoNANSS: a regional contribution to

ESC 2010 - ES2/P2/ID197
RÉSoNANSS: a regional contribution to
seismological observations in the Western
France
Éric Beucler, Marie Macquet, Antoine Mocquet and Mélanie Drilleau
Laboratoire de Planétologie et Géodynamique de Nantes (LPGNantes) UMR CNRS 6112 - Université de Nantes
The west metropolitan France is characterized by a persistent intraplate seismicity: ∼ 80 events of M ≤ 2 /year
and few greater magnitudes (only ve
Mw > 4 over the 20 last years, Fig. 2).
Due to a lack of coverage in the permanent seismological stations, the source
parameters are not accurately resolved.
Thanks to various fundings, the LPGNantes acquired a portable array of
12 short-period seismometers in order
to improve the coverage in the Brittany area. Our network (named RÉSoNANSS) is deployed around specic geological targets for several months, with
a spacing of ∼ 30 km. The rst deployment was focused on the Southern Armorican Shear Zone (SASZ, South Brittany). It allows us to precise the spatial distribution of the seismicity along
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the Hercynian structures. Within the
SI-HEX project, 19 typical intraplate
events are relocated using the RÉSoNANSS database. Some slight modications in the locations of earthquakes
can be observed (Fig. 3) and some comprehensive explorations of the model
space underline a typical pattern for the
Brittany crust model (Figs. 5, 6).
5˚W
50˚N
•
•
•
•
•
•
Seismicitiy in the western Europe, between
01/01/1980 and 12/31/2009 (M > 2.5). IRIS database.
Fig. 1:
OSIRIS stations
(Agecodagis);
3/6 phys channels;
SR @ 1. . . 2000 Hz;
Dyn. range :
128 dB @ 100 Hz;
NoeMax sensors up to
20 s;
continous recording;
6 xed stations and 6 devoted to be deployed on
various targets.
4˚W
3˚W
2˚W
1˚W
0˚
50˚N
• 12
4˚W
3˚W
2˚W
1˚W
49˚N
SAINT−BRIEUC
BREST
RENNES
48˚N
48˚N
LORIENT
VANNES
ANGERS
km
47˚N
0
50
NANTES
47˚N
100
LA ROCHE/YON
2010 Sep 02 10:37:23
5˚W
CEA/DASE
4˚W
3˚W
RéNaSS (CP)
2˚W
1˚W
RLBP (RESIF LB)
0˚
RÉSoNANSS
Seismicity in the western part of the France (2392
events) between 01/01/1980 and 06/10/2010. Magnitudes
are between 1.5 and 5.4, BCSF (RéNaSS+CEA) database.
The triangles represent the permanent and temporary seismological stations used, RÉSoNANSS is deployed since the
06/01/2007.
Fig. 2:
25 %
15 %
MFF
5˚W
49˚N
49˚N
0˚
20 %
Frequency
200
LDF
FLN
150
10 %
15 %
10 %
5%
5%
Epicentral distance (km)
06/27/2007
48˚N
1.64 1.66 1.68 1.70 1.72 1.74 1.76
OUDF
ROSF + BERZ
5.8
6.0
6.2
6.4
VP1 (km/s)
20 %
QUIF
15 %
Frequency
TOUC
PTMH + CATI
SGMF
50
KERB
ANNE
NENO
P1PO
46˚N
5˚W
2010 Sep 02 16:43:35
3˚W
2˚W
1˚W
50 %
20 %
0
0˚
Relocation of 22 intraplate events that occured
between the 27th June 2007 and the 30th June 2010 (BCSF
database). The new locations are plotted in red, compared
to the orange ones. The ellipses represent a condence of
∼ 95% (2 σ ), the inversion code for location is hyp2000.
50
30 %
40 %
25 %
10 %
35 %
20 %
15 %
5%
20 %
Frequency
35 %
10 %
30 %
25 %
15 %
20 %
10 %
15 %
5%
0%
5.4
5.6
5.8
6.0
6.2
0%
0%
6.4
1.64 1.66 1.68 1.70 1.72 1.74 1.76
VP1 (km/s)
VP /VS
5.4
5.6
5.8
6.0
6.2
6.4
5%
0%
0%
z1 (km)
6.0 6.2 6.4 6.6 6.8 7.0 7.2 7.4 7.6 7.8 8.0
VP2 (km/s)
Frequency
10 %
5%
0%
0%
1.64 1.66 1.68 1.70 1.72 1.74 1.76
VP /VS
5.4
5.6
5.8
6.0
6.2
6.4
VP1 (km/s)
Systematic exploration of the model space for the 27th June 2007
and the 12th April 2008 earthquakes (green and violet stars in Fig. 3,
respectively). VP1 is the velocity in the shallowest layer since only Pg
and Sg phases have been picked.
Fig. 5:
• Dipping interface between up-
per and lower crust?
5%
5%
0%
0%
14 16 18 20 22 24 26 28 30 32 34 36
z1 (km)
• Small VP /VS value, anisotropy?
Strongly heterogeneous crust?
VP1 (km/s)
15 %
14 16 18 20 22 24 26 28 30 32 34 36
5%
10 %
5%
5%
0%
VP /VS
10 %
5%
100
Seismograms of the 27th June
2007 8:50 Ml = 2.6 (near Redon, green
star in Fig. 3) earthquake (vertical components). The RÉSoNANSS stations are
labelled in black and the CEA/DASE in
red.
25 %
40 %
Time (s)
Fig. 4:
45 %
15 %
1.64 1.66 1.68 1.70 1.72 1.74 1.76
10 %
0
4˚W
Fig. 3:
Frequency
5.6
15 %
MLUC
47˚N
Frequency
5.4
VP /VS
100
6.0 6.2 6.4 6.6 6.8 7.0 7.2 7.4 7.6 7.8 8.0
VP2 (km/s)
Systematic exploration of the model space for the 12th July 2007 (left)
and the 23rd August 2008 (right) (maroon and blue stars in Fig. 3, respectively).
z1 is the thickness of the shallowest layer and V P2 the velocity in the medium
below.
Fig. 6:
0%
0%
GRR
This research has been realized within the SI-Hex
project and thanks to various fundings for the installation and the maintenance of RÉSoNANSS.