fault plane where an overall upward migration of activity was observed (first events at the bottom and last events at the top of the activated fault patch). France In Alpes-de-Haute-Provence, the Ubaye Valley is the most active seismic zone in the French Alps. Earthquakes can follow there the classical scheme "mainshock + aftershocks" (for instance the 1959 M5.5 earthquake, which caused heavy damage and two casualties). But seismic energy is principally released by swarms. This is particularly the case in the upper valley, between Barcelonnette and the French-Italian border. At the beginning of the 21st century, La Condamine-Châtelard experienced an exceptional swarm activity in an area where usually only a few low-magnitude events occur every year. A first swarm developed in 2003–2004 when more than 16,000 events were detected by the local monitoring network, but with magnitudes keeping to low values (2.7). On a map, the 2003–2004 swarm is 8-km long. After a period of almost complete inactivity, it was followed by a second swarm (2012–2014), slightly offset by a few kilometres, and with a length of 11 km. This second swarm was initiated by an M4.3 earthquake in February 2012. Another M4.8 earthquake in April 2014 reactivated the swarm in 2014–2015. These two major shocks, which caused damage in the nearby localities, were of course followed by their own short sequence of aftershocks, but such a 4-year activity for moderate magnitude shocks clearly characterizes a swarm. Most foci were located in the 4–11-km depth range, within the crystalline basement. Focal mechanisms involve normal faulting, but also strike-slip faulting. In the lower Rhône Valley, the Tricastin has been known from the 18th century as the seat of earthquake swarms which sometimes caused damage, as in 1772–1773 and 1933–1936, and which were characterized by barrage-like detonations—at least so reported by the inhabitants. No seismic activity had been documented in the region since 1936, when a very weak swarm appeared for a few months in 2002–2003 (maximal magnitude 1.7). Had their foci not been sited just under a hamlet in the vicinity of Clansayes, and very close to the surface (200 m deep), these shocks would have gone unnoticed. In such a scenario of "ultra-shallow" seismicity, even earthquakes of very low magnitude (1, or 0, or even negative magnitude) can be felt as explosions or water-hammer noises, more than as vibrations. Most foci were located in an Upper-Cretaceous reef-limestone slab which bursts