Constraining seismogenic potential in an intraplate domain. Examples of methods and limitations from the Jasneuf Fault (Western Alps, France) and the Toulaud Fault (Massif Central, France)

Présentation de Jérémy Billant (Cerege) au 1er Workshop Résif "Aléa sismique" | 27 et 28 septembre 2016, Strasbourg

Transcript

1. Constraining seismogenic potential in an intraplate domain. Examples of methods and limitations from the Jasneuf Fault (Western Alps, France) and the Toulaud Fault (Massif Central, France) - J. Billant , O. Bellier, F. Thomas , V. Godard , J.C. Hippolyte P. Dussouillez, F. Hollender , K. Manchuel
2. 2 Géologie : Bodelle and Goguel (1980) Catalogues : SISFRANCE (Scotti et al., 2004), Si-Hex (Cara et al., 2015) Mécanismes au foyer : Baroux et al. (2001), Eva et Solarino (1998), Fréchet et al. (1996, 2010), Kastrup et al. (2004), Ménard (1988), Nicolas et al. (1990), Sue et al. (1999), Thouvenot (1996), Thouvenot et al. (1998, 2003) Objectifs - localiser et contraindre la géométrie des failles constitutives du système de failles de Belledonne - contraindre leur cinématique, l'état de contrainte, identifier des indices de déformation récente, quantifier les déplacements finis et les vitesses de glissement - déterminer comportement sismogénique et déformation - estimer des magnitudes potentielles et des temps de retour des séismes
3. 3 • Les taux d'érosion (sur 10 derniers ka 0,06 à 2,1 mm/an) proches des taux de déformation (0,1 à <5 mm/an pour 10-20 km) limitent l'approche morphotectonique => fort rafraîchissement attendu des indices de déformation récente • Les faibles taux de déformation impliquent que les catalogues sismiques n'ont pas encore enregistrés de cycle complets => méconnaissance des magnitudes maximales et des temps de retour • => Besoin de croiser les outils et les méthodes : - tectonique et analyse structurale - mesure de fracturations et cinématique de faille - géologie du Quaternaire et morphotectonique plio-quaternaire - géomorphologie qualitative et quantitative - prospection géophysique
4. 4 Géologie : Bodelle and Goguel (1980) Catalogues : SISFRANCE (Scotti et al., 2004), Si-Hex (Cara et al., 2015) Mécanismes au foyer : Ménard (1988), Nicolas et al. (1990), Thouvenot et al. (2003) Failles de la Cléry et du Jasneuf
5. 5 Les failles de la Cléry et du Jasneuf – Cinématique et états de contraintes
6. 6 Faille du Jasneuf – Analyses morphologiques
7. 7 Faille du Jasneuf – Analyses morphologiques Un segment principal d'au moins 7,5 km
8. 8 Faille du Jasneuf – Analyses morphologiques Décalage total des falaises : 715 ± 45 m
9. 9 Faille du Jasneuf – Analyses morphologiques RDV à la RST 2016 16.9±2.9m 45±3.5m 10.6±1.6m ?
10. 10 Faille du Jasneuf – Vitesse de déplacement et potentiel sismogénique D'après les lois de Wells et Coppersmith (1994) : Pour un plan de faille de 48,7 km² (7,5 km L x 6,5 km H): Mw max = 5,7 Pour une vitesse de 0,13±0,03 mm.an-1 : temps de retour = ~ 500 ans ~ -6,5 km
11. 11 Faille de Toulaud
12. 12 Faille de Toulaud
13. 13 Faille de Toulaud Mesures H/V : (Vs = 1300 m/s, Schlupp et al., 2001, Bailly et al.,2013) NW : 0.71±0.02 Hz Altitude : ~ -236m SE : 0.74±0.02 Hz Altitude : ~ -254m Décalage vertical de ~18m
14. 14 Faille de Toulaud
15. 15 Faille de Toulaud Décalage senestre de ~130m Vitesse : ~0,02 mm.an-1
16. 16 Apports du travail • Identification de nouvelle failles potentiellement sismogènes Apports du travail • Les vitesses sont calculées sur le long terme, dans les deux cas sur ~5,6 Ma • Faille du Jasneuf : - creeping ? - géométrie non contrainte
17. 17 Merci
18. Constraining seismogenic potential in an intraplate domain. Examples of methods and limitations from the Jasneuf Fault (Western Alps, France) and the Toulaud Fault (Massif Central, France) - J. Billant , O. Bellier, F. Thomas , V. Godard , J.C. Hippolyte P. Dussouillez, F. Hollender , K. Manchuel
19. 2 Géologie : Bodelle and Goguel (1980) Catalogues : SISFRANCE (Scotti et al., 2004), Si-Hex (Cara et al., 2015) Mécanismes au foyer : Baroux et al. (2001), Eva et Solarino (1998), Fréchet et al. (1996, 2010), Kastrup et al. (2004), Ménard (1988), Nicolas et al. (1990), Sue et al. (1999), Thouvenot (1996), Thouvenot et al. (1998, 2003) Objectifs - localiser et contraindre la géométrie des failles constitutives du système de failles de Belledonne - contraindre leur cinématique, l'état de contrainte, identifier des indices de déformation récente, quantifier les déplacements finis et les vitesses de glissement - déterminer comportement sismogénique et déformation - estimer des magnitudes potentielles et des temps de retour des séismes This study is focused on a NE trending faulting system in the western Alps. MC, rhone, southern Jura, Penninic frontal thrust, external crystalline massif and the subalpine massif This fault system that we called the Belledonne fault system extent from the Aiguilles rouges and Mont-Blanc massif north-eastward to the Vercors massif to the south westward. Alps shows two major seismic regions delimited by the external crystalline massif. The first one, eastward of the penninic front, show extension regim sub-perpendicular to the relief. The second one, westward of the external crystalline massif, show a most diffuse seismicity, but mainly with strike slip faulting and thrusting. This second area correspond to the subalpine massif which are composed of the mesozoic to cenozoic cover deformed as fold and thusth belt during the late miocene. At the limit between the external crystalline massif and the subalpine massif, a higher density seismic alignement is apparent as you can see on the iso denity seismic contours. It correspond to the BBF, identified as a crustal dextral strike slip fault by Thouvenot et al thanks to a microseismic survey. Most of the earthquakes in this area occurs in the first ten kilometers depth and don't exceed a local magnitude of four. But the region also knows several stronger earthquakes with local magnitude close to five like the Vallorcine and Grand-bornand earthquakes or the 7.5 MSK intensity Emosson earthquake.
20. 3 • Les taux d'érosion (sur 10 derniers ka 0,06 à 2,1 mm/an) proches des taux de déformation (0,1 à <5 mm/an pour 10-20 km) limitent l'approche morphotectonique => fort rafraîchissement attendu des indices de déformation récente • Les faibles taux de déformation impliquent que les catalogues sismiques n'ont pas encore enregistrés de cycle complets => méconnaissance des magnitudes maximales et des temps de retour • => Besoin de croiser les outils et les méthodes : - tectonique et analyse structurale - mesure de fracturations et cinématique de faille - géologie du Quaternaire et morphotectonique plio-quaternaire - géomorphologie qualitative et quantitative - prospection géophysique Our objectives is to constrain localisation of the consitutive fault of the Belledonne fault system, know their geometry, find clues of recent deformation, quantify fault slip rate and estimate possible recurrence period. Because of the large study area, we focused our research on know fault, thanks to geological map, and area with strong earthquakes well documented. We try to locate morphologic expression of active faulting thanks to morphological analysis made on aerial photography and DEM and verify this observations with field survey. In order to quantify the deformation rate, we try to dated the morphological markers of deformation. We will see later that is a tricky task because of the lack of deformed late deposits. In order to check if morphologic markers of deformation are consistent with the fault kinematics, we made several microtectonic measurements and stress inversion.
21. 4 Géologie : Bodelle and Goguel (1980) Catalogues : SISFRANCE (Scotti et al., 2004), Si-Hex (Cara et al., 2015) Mécanismes au foyer : Ménard (1988), Nicolas et al. (1990), Thouvenot et al. (2003) Failles de la Cléry et du Jasneuf This two dextral strike slip faults cut the Vercors massif in the area called the Glandasse plateau. This large and flat plateau is composed of 200m thick limestones overlapping about 1000m thick marl series..
22. 5 Les failles de la Cléry et du Jasneuf – Cinématique et états de contraintes This two dextral strike slip faults cut the Vercors massif in the area called the Glandasse plateau. This large and flat plateau is composed of 200m thick limestones overlapping about 1000m thick marl series..
23. 6 Faille du Jasneuf – Analyses morphologiques We first found several morphologic clues of recent deformations on topographic map. Thanks to the low vegetation cover of the area, we computed a high resolution DEM and orthophotography using photogrammetry in order to better constrained fault mapping and geomorphic features of potential active tectonics. Resolution of the DEM is about 50 cm. We use this data to extract streams network. The first geomorphic features of active deformations are located along this N45°-E trending faults near the southern termination.
24. 7 Faille du Jasneuf – Analyses morphologiques Un segment principal d'au moins 7,5 km We first found several morphologic clues of recent deformations on topographic map. Thanks to the low vegetation cover of the area, we computed a high resolution DEM and orthophotography using photogrammetry in order to better constrained fault mapping and geomorphic features of potential active tectonics. Resolution of the DEM is about 50 cm. We use this data to extract streams network. The first geomorphic features of active deformations are located along this N45°-E trending faults near the southern termination.
25. 8 Faille du Jasneuf – Analyses morphologiques Décalage total des falaises : 715 ± 45 m The first morphological evidence of active deformation is the right lateral offset of the cliff on each faults segments. Offset is about 120 meters between cliffs 1 and 2, 100 meters between cliffs 2and 3 and 530 meters between cliffs 3 and 4. The total offset between cliffs 1 and 4 is about 750 meters. A talweg also shoxs a right lateral offset of about 600 meters which is the same orders of magnitude as the cliffs offset. If this features are really offsets, it is impossible that they are quaternary. This cliffs were probably formed during the incision of the Drôme river which probably occurs during the messinian salinity crisis and/or the Alpine orogeny. In this case, considering a 750 meters total offset, fault slip rate is closed to 0.1 mm/yr. At a larger scale, topography also shows several anomalies which we interpreted as recent fault scarps. You can see here several short fault consistent with a P Riedel arrangement consistent with right lateral strike slip faulting of the N45° E trending faults. A 40 meters right lateral offset of the topographic contours are clearly visible on each side of this faults. Moreover, one of the P shear fault also show a right lateral offset of the topographic contours of about 15 meters. This first two observations are consitent with recent dextral strike slip faulting of the area.
26. 9 Faille du Jasneuf – Analyses morphologiques RDV à la RST 2016 16.9±2.9m 45±3.5m 10.6±1.6m ? This fault also shows several morphologic features offset.
27. 10 Faille du Jasneuf – Vitesse de déplacement et potentiel sismogénique D'après les lois de Wells et Coppersmith (1994) : Pour un plan de faille de 48,7 km² (7,5 km L x 6,5 km H): Mw max = 5,7 Pour une vitesse de 0,13±0,03 mm.an-1 : temps de retour = ~ 500 ans ~ -6,5 km Nevertheless, we propose that this features could really be morphological features offset by the left lateral strik slip movement along the Brion fault. Indeed, this area is located at the southern termination of the Isere glacier which have infilled the Grésivaudan valley during Wurmian AND rissian period with approximately the same extension and with a southward flow direction. Assuming the formation of the glacial valley during a glacial period prior to the wurmian one, the flanck could have been offset during an interglacial period and preserved because of lower erosion rate. During a second glacial period, infilled again by a glacier. The western flancks, exposed to the glacial flow, were eroded whereas the estern one were protected. This scenario could have been repeated during several glacial period and maybe during each glacial stade because the area is pretty closed to termination of the Isere glacier. We can not allow an age of the formation of the flanck of the glacial valley, but calculated fault slip rate become closed to 1mm/yr if we consider that they were formed during the first Rissian stade which occur there is 400 000 years BP.
28. 11 Faille de Toulaud
29. 12 Faille de Toulaud
30. 13 Faille de Toulaud Mesures H/V : (Vs = 1300 m/s, Schlupp et al., 2001, Bailly et al.,2013) NW : 0.71±0.02 Hz Altitude : ~ -236m SE : 0.74±0.02 Hz Altitude : ~ -254m Décalage vertical de ~18m
31. 14 Faille de Toulaud
32. 15 Faille de Toulaud Décalage senestre de ~130m Vitesse : ~0,02 mm.an-1
33. 16 Apports du travail • Identification de nouvelle failles potentiellement sismogènes Apports du travail • Les vitesses sont calculées sur le long terme, dans les deux cas sur ~5,6 Ma • Faille du Jasneuf : - creeping ? - géométrie non contrainte
34. 17 Merci