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The 16,000-event 2003–2004 earthquake swarm in Ubaye (French Alps)

Abstract : The Ubaye valley, one of the most active seismic zones in the French Alps, was visited in 2003–2004 by a prolific and protracted earthquake swarm with a maximum magnitude M L = 2.7. The seismic activity clustered along a 9-km-long, 3- to 8-km-deep rupture zone which trends NW-SE across the valley and dips 80°SW. Focal mechanisms for the larger shocks show either normal faulting with a SW-NE trending extension direction or NW-SE strike slip with right lateral displacement. The activity initiated in the central part of the rupture zone, diffused to its periphery, and eventually concentrated in its southeastern deeper part. A permanent station situated above the swarm allowed us to monitor the entire phenomenon from its inception to its conclusion. The complete time series includes more than 16,000 events, with shocks down to magnitude M L = −1.3. It shows bursts of activity, separated by quiescent periods, with no well-defined subswarms as observed in other similar studies. The Gutenberg-Richter b value significantly varied between 1.0 and 1.5 in the course of the phenomenon
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Submitted on : Thursday, June 3, 2021 - 11:53:15 AM
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L. Jenatton, Robert Guiguet, François Thouvenot, N. Daix. The 16,000-event 2003–2004 earthquake swarm in Ubaye (French Alps). Geophysical Research Letters, American Geophysical Union, 2007, 112, pp.B11304. ⟨10.1029/2006JB004878⟩. ⟨insu-00346285⟩



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