Tectonic stress regime in the 2003-2004 and 2012-2015 earthquake swarms in the Ubaye Valley, French Alps

0494880 - GFÚ 2019 RIV CH eng J - Journal Article
Fojtíková, Lucia - Vavryčuk, Václav
Tectonic stress regime in the 2003-2004 and 2012-2015 earthquake swarms in the Ubaye Valley, French Alps.
Pure and Applied Geophysics. Roč. 175, č. 6 (2018), s. 1997-2008. ISSN 0033-4553. E-ISSN 1420-9136
R&D Projects: GA ČR GAP210/12/2336; GA ČR GC16-19751J
Institutional support: RVO:67985891 ; RVO:67985530
Keywords : Ubaye Valley * south-western Alps * earthquake swarm * focal mechanism * stress inversion * fluids
OECD category: Volcanology; Geology (USMH-B)
Impact factor: 1.466, year: 2018

We study two earthquake swarms that occurred in the Ubaye Valley, French Alps within the past decade: the 2003-2004 earthquake swarm with the strongest shock of magnitude ML = 2.7, and the 2012-2015 earthquake swarm with the strongest shock of magnitude ML = 4.8. The 2003-2004 seismic activity clustered along a 9-km-long rupture zone at depth between 3 and 8 km. The 2012-2015 activity occurred a few kilometres to the northwest from the previous one. We applied the iterative joint inversion for stress and fault orientations developed by Vavryuk (2014) to focal mechanisms of 74 events of the 2003-2004 swarm and of 13 strongest events of the 2012-2015 swarm. The retrieved stress regime is consistent for both seismic activities. The sigma (3) principal axis is nearly horizontal with azimuth of similar to 103A degrees. The sigma (1) and sigma (2) principal axes are inclined and their stress magnitudes are similar. The active faults are optimally oriented for shear faulting with respect to tectonic stress and differ from major fault systems known from geological mapping in the region. The estimated low value of friction coefficient at the faults 0.2-0.3 supports an idea of seismic activity triggered or strongly affected by presence of fluids.
Permanent Link: http://hdl.handle.net/11104/0287933