Search

Mud volcanoes are fluid escape structures allowing for surface venting of hydrocarbons (mostly gas but also liquid condensates and oils) and water–sediment slurries. For a better understanding of mud volcano dynamics, the characterization of the fluid dynamics within mud volcano conduits; the presence, extent, and depth of the fluid reservoirs; and the connection among aquifers, conduits, and mud reservoirs play a key role. To this aim, we performed a geoelectrical survey in the Nirano Salse Regional Nature Reserve, located at the edge of the northern Apennines (Fiorano Modenese, Italy), an area characterized by several active mud fluid vents. This study, for the first time, images the resistivity structure of the subsoil along two perpendicular cross sections down to a depth of 250 m. The electrical models show a clear difference between the northern and southern sectors of the area, where the latter hosts the main discontinuities. Shallow reservoirs, where fluid muds accumulate, are spatially associated with the main fault/fracture controlling the migration routes associated with surface venting and converge at depth towards a common clayey horizon. There is no evidence of a shallow mud caldera below the Nirano area. These findings represent a step forward in the comprehension of the Nirano Salse plumbing system and in pinpointing local site hazards, which promotes safer tourist access to the area along restricted routes. [ABSTRACT FROM AUTHOR]

The Central Apennines, Italy, are characterized by moderate seismic activity on normal faults, oriented in directions parallel to the Apenninic chain. The subject of this study is the Umbria-Marche Apennines, a segment approximately 200-km long, where three main seismic events occurred in the last three decades. The 1979 Norcia earthquake was a M w = 5.8 event, taking place at the south end of the considered segment. The 1984 Gubbio earthquake was a M w = 5.6 event which took place at the north end. The 1997-1998 Colfiorito sequence constituted 8 main shocks with magnitudes M w between 5 and 6 and epicenters located between the Gubbio and the Norcia earthquake areas. A model made of an elastic half-space is considered, in which the seismic sources are represented by rectangular dislocations which have the appropriate values of source parameters, and in which the static stress field produced by each event is calculated. The analysis of the Coulomb stress change (Δ C) as a function of time shows that the coseismic stress transfer and fault interaction played an important role in the region during the past three decades: 7 earthquakes of the 9 considered took place where Δ C>0. Such an interaction has been confirmed by the analysis of the aftershocks in the Colfiorito zone post September 26, 1997: about the 61% of the aftershocks considered took place where Δ C>0. The comparison between the Δ C s due to the coseismic stress transfer and the rate Δ Ċ t due to the tectonic stress allows us to quantify the time advance of the earthquakes. The Δ C s pattern shows positive values in two areas that can be regarded as historical seismic gaps. [ABSTRACT FROM AUTHOR]