The plan view architecture of the Soddo margin is characterized by per typical array of sigmoidal, right-stepping en-echelon normal or oblique faults (Figure 5)
Sopra order to better characterize the distribution of vents sopra the area and onesto better define their relations with faults, we have mapped vent alignments and assessed their reliability according esatto the procedure illustrated con Paulsen and Wilson [ 2010 ]. Vent mapping has been performed on available pianeta images (Landsat TM, Aster, Google Earth imagery), digital elevation models (DEMs; SRTM, Aster), and aerial photos. Sopra particular, vent alignments have been mapped on the basis of the spatial distribution of vents as well as their shapes (vent elongation provides verso critical parameter puro group single vents into an alignment). Reliability of vent alignments has been defined according esatto parameters such as number of vents, number and characteristics of elongate vents (vents are considered elongate when the ratio between the lengths of the vietnamcupid maximum and minimum axes is >1.2), norma deviation from a best fit line, etc. [see Paulsen and Wilson, 2010 ]. The result of this analysis is illustrated sopra Table 3 and sopra the graph of Figure 12d, where the azimuthal distribution of elongate vent long axis has also been reported. The distribution of both vent alignments and elongate vent long axis shows a main peak at N20°–25°Anche, indicating verso striking correspondence with the andamento of the border faults mediante the sezione (amico Figure 12d with Figure 5c) and thus strengthening the close relations between faulting and volcanism. Onesto complete the analysis, we have also calculated the azimuthal distribution of cone breaching, whose results are shown durante the graph of Figure 12e. This analysis indicates that the andamento of cone breaching tends to parallelize vent alignments (as well as the inclinazione of border faults), with verso minor peak orthogonal puro this latter trend. Both observations are con agreement with theoretical predictions [Tibaldi, 1995 ].
- per Adapted from Paulsen and Wilson . Latitude and longitude of alignment locations garantis WGS84 datum.
- b B, basalts; R, rhyolites.
- c A vent is considered elongated when the ratio between the lengths of the maximum and minimum axes of the best fit ellipse matching the mapped shape of the vent is>1.2.
- d Fissure ridge.
- ancora Reliability grade: A> B> C> D.
5 Conversation
The collected giorno illustrate significant Late Pleistocene-Holocene tectonic activity of the western margin close sicuro Soddo, where radiometric dating of faulted material indicates Late Pleistocene-Holocene (post-30 ka) fault activity. This supports inferences based on analysis of historical seismicity [Gouin, 1979 ; Keir et al., 2006 ], morphotectonic investigations [Boccaletti et al., 1998 ], and recent Gps giorno [Kogan et al., 2012 ] suggesting active deformation along the western rift margin of the Southern MER. Although not quantifiable because of the lack of subsurface information, deformation is apparently subordinate at the rift axis, where the recent tectono-magmatic activity is likely related esatto incipient WFB faulting as hypothesized for the Central MER [Agostini et al., 2011a ]. These findings support models that predict a transition from axial tectono-magmatic deformation durante the Northern MER puro marginal deformation con the Central and Southern MER, sopra turn indicating an along-axis, north puro south decrease durante rift maturity con the MER [addirittura.g., Hayward and Ebinger, 1996 ; Corti, 2009 ; Agostini et al., 2011a ].
The rift margin at Soddo is characterized by the lack of a major rift escarpment with a gentle transition between the rift floor and the plateau accommodated by numerous faults (Figure 4) with limited lateral extent (maximum length in the range of a few kilometers) and small vertical offset (typically <100>1000 m) give rise to prominent fault escarpments. Comparison of this architecture with the deformation resulting from analog models of rifting indicates that the fault pattern has been controlled by a sub-E-W (N95°E to N100°E) extension direction, resulting in an oblique extension with respect to the roughly NE-SW-trending rift. This well accords with inversion of fault slip data collected on faults with Pleistocene-Holocene activity, which indicates a N105°E-directed extension (Figure 3), with local variations in the paleostress field likely resulting from stress reorientations and/or influence of volcanic activity [e.g., Acocella et al., 2011 ]. These results are strikingly similar to recent GPS data from the Southern MER [Kogan et al., 2012 ], which also indicate a current N100°E-directed extension at the latitude of Arba Minch (
