Mid-ocean ridges are segmented and offset along their length. However, the processes leading to growth of the segments and linkage of deformation between offsets are still debated. The continental rift of Afar offers an opportunity to observe these processes, showing tectonic and magmatic features similar to that observed at slow-spreading mid-ocean ridges. The Afar depression results from the divergence of the Nubian, Arabian and Somalian plates along the Red Sea, Gulf of Aden and Main Ethiopian rift arms during the last 30 My. Along the Erta Ale ridge in Northern Afar the extension along the plate boundary is ~N60°E and is focused in ~20km-wide, ~70km-long en-echelon magmatic segments. The surface morphology of the segments is dominated by NNE striking cone fields, and fractures cutting Holocene basaltic lava flows. Here we used InSAR, seismicity, and structural data from analysis of satellite imagery and field measurements to study the deformation in the area connecting the Erta Ale and Tat Ali segments of northern Afar. Modelling of InSAR measurements from co-seismic deformation of a ML ~5.0 earthquake in October 2007 shows mainly oblique left-lateral slip along ~N-S-oriented faults, similar to the source mechanism achieved from seismic moment tensor inversion. Structural analysis and field measurements of left-lateral shear, such as horsetailtype fault tips and lozenge-shape structures were also observed, in agreement with geodetic observations. However, orientation of faults planes based on analysis of satellite imagery combined with local earthquake focal mechanisms during 2011/2012 shows evidence for right-lateral slip on conjugate NW-SE striking faults in the same region (Illsley-Kemp et al., 2018). Both InSAR and structural data indicate a local extension with direction ~N50°E in the region connecting the two rift segments, hence oblique to the faults. Our observations are consistent with a model of rift linkage through a dextral oblique transfer zone, causing counter-clockwise rotation of the extension direction. We conclude that oblique slip occurs on a conjugate fault set in the offset zone connecting the Erta Ale and Tat Ali segments.
Growth of a sinkhole in a seismic zone of the northern Apennines (Italy)
La Rosa A.Primo
;Pagli C.Secondo
;Molli G.;D’amato Avanzi G.Ultimo
2019-01-01
Abstract
Mid-ocean ridges are segmented and offset along their length. However, the processes leading to growth of the segments and linkage of deformation between offsets are still debated. The continental rift of Afar offers an opportunity to observe these processes, showing tectonic and magmatic features similar to that observed at slow-spreading mid-ocean ridges. The Afar depression results from the divergence of the Nubian, Arabian and Somalian plates along the Red Sea, Gulf of Aden and Main Ethiopian rift arms during the last 30 My. Along the Erta Ale ridge in Northern Afar the extension along the plate boundary is ~N60°E and is focused in ~20km-wide, ~70km-long en-echelon magmatic segments. The surface morphology of the segments is dominated by NNE striking cone fields, and fractures cutting Holocene basaltic lava flows. Here we used InSAR, seismicity, and structural data from analysis of satellite imagery and field measurements to study the deformation in the area connecting the Erta Ale and Tat Ali segments of northern Afar. Modelling of InSAR measurements from co-seismic deformation of a ML ~5.0 earthquake in October 2007 shows mainly oblique left-lateral slip along ~N-S-oriented faults, similar to the source mechanism achieved from seismic moment tensor inversion. Structural analysis and field measurements of left-lateral shear, such as horsetailtype fault tips and lozenge-shape structures were also observed, in agreement with geodetic observations. However, orientation of faults planes based on analysis of satellite imagery combined with local earthquake focal mechanisms during 2011/2012 shows evidence for right-lateral slip on conjugate NW-SE striking faults in the same region (Illsley-Kemp et al., 2018). Both InSAR and structural data indicate a local extension with direction ~N50°E in the region connecting the two rift segments, hence oblique to the faults. Our observations are consistent with a model of rift linkage through a dextral oblique transfer zone, causing counter-clockwise rotation of the extension direction. We conclude that oblique slip occurs on a conjugate fault set in the offset zone connecting the Erta Ale and Tat Ali segments.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
