The plan view architecture of the Soddo margin is characterized by verso typical array of sigmoidal, right-stepping en-echelon normal or oblique faults (Figure 5)
Sopra order puro better characterize the distribution of vents con the settore and puro better define their relations with faults, we have mapped vent alignments and assessed their reliability according onesto the procedure illustrated per Paulsen and Wilson [ 2010 ]. Vent mapping has been performed on available corpo celeste images (Landsat TM, Aster, Google Earth imagery), digital elevation models (DEMs; SRTM, Aster), and aerial photos. In particular, vent alignments have been mapped on the basis of the spatial distribution of vents as well as their shapes (vent elongation provides per critical parameter to group celibe vents into an alignment). Reliability of vent alignments has been defined according onesto parameters such as number of vents, number and characteristics of elongate vents (vents are considered elongate when the ratio between the lengths of the maximum and minimum axes is >1.2), standard deviation from a best fit line, etc. [see Paulsen and Wilson, 2010 ]. The result of this analysis is illustrated per 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 per main peak at N20°–25°E, indicating a striking correspondence with the trend of the border faults durante the reparto (complice Figure 12d with Figure 5c) and thus strengthening the close relations between faulting and volcanism. Esatto complete the analysis, we have also calculated the azimuthal distribution of cone breaching, whose results are shown con the graph of Figure 12e. This analysis indicates that the trend of cone breaching tends preciso parallelize vent alignments (as well as the tendenza of border faults), with a minor peak orthogonal puro this latter andamento. Both observations are sopra agreement with theoretical predictions [Tibaldi, 1995 ].
- a Adapted from Paulsen and Wilson . Latitude and longitude of alignment locations assume WGS84 datum.
- b B, basalts; R, rhyolites.
- c Verso 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.
- di nuovo Reliability grade: A> B> C> D.
The collected giorno illustrate significant Late Pleistocene-Holocene tectonic activity of the western margin close puro Soddo, where radiometric funziona alua 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 Esploratore datazione [Kogan et al., 2012 ] suggesting adroite 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 preciso incipient WFB faulting as hypothesized for the Central MER [Agostini et al., 2011a ]. These findings support models that predict verso transition from axial tectono-magmatic deformation per the Northern MER puro marginal deformation sopra the Central and Southern MER, mediante turn indicating an along-axis, north to south decrease in rift maturity mediante the MER [e.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 (