Combined Seismic and Geodetic Observations of Dike Injection in the Dabbahu Rift Segment, Afar, Ethiopia
Abstract
As rifting proceeds to breakup, strain localizes to discrete, narrow rift segments by a combination of diking and faulting. However, the controls on the kinematics and dynamics of rifting episodes are poorly understood. We integrate new seismic and geodetic data from the Dabbahu rift segment, Afar, to constrain the location of magma sources, and the spatial/temporal variability of diking and faulting just prior to the onset of sea-floor spreading. Since 4Ma, strain in north Afar has localized to 60-km-long rift segments that are similar in size and morphology to slow-spreading mid-ocean ridge segments. In June2006 vigorous deformation occured near AdoAle volcano, in the center of the Dabbahu rift segment. InSAR shows 2.5m opening along a 10km-long zone, with no evidence of deflation of shallow chambers beneath central volcanoes. Deformation is consistent with injection of a 2m- wide dike at 1-10km depth. Seismic and GPS data constrain the spatial/temporal evolution of deformation. Starting midday 17th June, ML<3 earthquakes occur at the southern end of the deforming zone. After 1hr, earthquake merge into tremor, increase in magnitude, and migrate 10km NNW over 4hrs. Earthquakes are likely caused by inflation induced tension at the tip of a laterally propagating dike. Prior to June, broad deformation is observed beneath AdoAle, consistent with inflation of a source zone 10-15km deep beneath the central portion of the rift segment. The June06 dike is the first of 6 major intrusions in the Dabbahu rift since Sep05, a pattern similar to the 1975-84 rifting event in Krafla, Iceland. Our results show that during continental rupture strain is accommodated by repeated injection of dikes and induced faulting. Magma may be sourced directly to the center of the rift segment from reservoirs in the upper mantle and/or lower crust and delivered into the upper 10km by the lateral injection of discrete dikes.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2007
- Bibcode:
- 2007AGUFM.T31F..06K
- Keywords:
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- 1209 Tectonic deformation (6924);
- 7230 Seismicity and tectonics (1207;
- 1217;
- 1240;
- 1242);
- 7290 Computational seismology;
- 8109 Continental tectonics: extensional (0905);
- 8178 Tectonics and magmatism